UNIVERSITI TEKNOLOGI MARA DESIGN OF PLASMA ANTENNA FOR RECONFIGURABLE BEAM STEERING TECHNIQUE HAJAR BINTI JA AFAR. PhD

Transcription

1 UNIVERSITI TEKNOLOGI MARA DESIGN OF PLASMA ANTENNA FOR RECONFIGURABLE BEAM STEERING TECHNIQUE HAJAR BINTI JA AFAR PhD January

2 UNIVERSITI TEKNOLOGI MARA DESIGN OF PLASMA ANTENNA FOR RECONFIGURABLE BEAM STEERING TECHNIQUE HAJAR BINTI JA AFAR Thesis submitted in fulfillment of the requirement for the degree of Doctor of Philosophy Faculty of Electrical Engineering January 2016 i

3 CONFIRMATION BY PANEL OF EXAMINERS I certify that a Panel of Examiners has met on 22 October 2015 to conduct the final examination of Hajar Binti Ja afar on her Doctor of Philosophy thesis entitled "Design of Plasma Antenna For Reconfigurable Beam Steering Technique in accordance with Universiti Teknologi MARA Act 1976 (Akta 173). The Panel of Examiners recommends that the student be awarded the relevant degree. The panel of Examiners was as follows: Datin Shah Rizam Mohd Shah Baki,PhD Professor,Ir Faculty of Electrical Engineering Universiti Teknologi MARA (Chairman) Nur Emileen Abd Rashid, PhD Senior Lecturer Faculty of Electrical Engineering Universiti Teknologi MARA (Internal Examiner) Mohammad Tariqul Islam, PhD Professor Faculty of Engineering & Built Environment, Universiti Kebangsaan Malaysia, (External Examiner) SAULEAU, Ronan, PhD Professor Antennes et Dispositifs Hyperfréquences University of Rennes 1 (UR1) (External Examiner) SITI HALIJJAH SHARIFF, PhD Associate Professor Dean Institute of Graduate Studies Universiti Teknologi MARA Date : 11 th January 2016 ii

4 AUTHOR S DECLARATION I declare that the work in this thesis was carried out in accordance with the regulations of Universiti Teknologi MARA. It is original and is the results of my own work, unless otherwise indicated or acknowledge as referenced work. This thesis has not been submitted to any other academic institution or non-academic institution for any degree or qualification. I, hereby, acknowledge that I have been supplied with the Academic Rules and Regulations for Post Graduate, Universiti Teknologi MARA, regulating the conduct of my study and research. Name of Student : Hajar Binti Ja afar Student I.D No : Programme : Doctor of Philosophy (Electrical Engineering) Faculty : Faculty of Electrical Engineering Thesis Title : Design of Plasma Antenna for Reconfigurable Beam Steering Technique Signature of Student : Date : January 2016 iii

5 ABSTRACT The industrial potential of plasma technology is well known and excellent demonstrated in several processes of microwave technology, which incorporate some use of an ionized medium. In vast majority of approaches, the plasma, or ionized volume, simply replaced a solid conductor. Highly ionized plasma is essentially a good conductor, and therefore plasma filaments can serve as transmission line elements for guiding waves, or antenna surfaces for radiation. Plasma antenna is a kind of antenna that radiate electromagnetic wave (EM) energy based on ionized gas instead of metallic conductor in antenna design. In this research work, the development using plasma medium as a conductor element instead of metal medium is investigated. Three new design antenna by using plasma concepts were proposed; namely cylindrical monopole plasma antenna using electrode-less discharge tube, monopole plasma antenna using fluorescent tube and reconfigurable plasma antenna array. The research described in this project introduces the analysis of cylindrical monopole plasma antenna. Three types of gases with three different pressure which are Argon gas, Neon gas and Hg-Ar gas (mixture of Argon gas and mercury vapor) with pressure at 0.5 Torr, 5 Torr and 15 Torr respectively is used in this research to observe the interaction between plasma medium and radio frequency (RF) signal. The containers that use to fill the gas are namely electrode-less discharge tube. The technique that used in this experiment to generate plasma is using Dielectric Barrier Discharge (DBD). The monopole plasma antenna using fluorescent tube is designed at frequency 2.4 GHz which is aim in wireless application. The commercially fluorescent lamp is used as a plasma antenna. Coupling technique was used in this design. In the reconfigurable plasma antenna array, the behavior of the reconfigurable antenna array system using plasma medium has been investigated and discuss with respect to the beam shaping characteristics. The reconfigurable plasma antenna array is capable of scanning the radiation pattern over 360. These results confirm that the main beam directions can be directed in the following directions depending on the states of switches which are 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300 and 330. The simulated and measured results are presented and compared, to demonstrate the performance of the proposed antennas. iv

6 ACKNOWLEDGEMENT In the name of Allah, the Most Gracious The Most Merciful. I am grateful for guidance and continuous supports from my supervisor, Assoc Prof. Dr. Mohd Tarmizi bin Ali. His inspiring advices and commitment during the period of this work are invaluable. My particular thanks go to my second supervisor, Dr. Ahmad Nazri bin Dagang, for his advices in numerous discussions especially on the plasma parts. My appreciations go to Mr Mohammad Khalim Kamsan, who helped me in the technical parts including fabrications and measurements and lab technicians for their guidance and assistance. I also appreciate to all my colleagues of Antenna Research Group (ARG), Microwave Technology Center (MTC), Faculty of Electrical Engineering, Universiti Teknologi MARA (UiTM), who have provided assistance and for the memorable time spent together throughout the 3 years. The sweet memories that we had shared are safely embedded in my heart and it will not be erased over time. I would like to acknowledge the Ministry of Higher Education, Malaysia and University Teknologi MARA,Malaysia (UiTM) for the financial support throughout my study. I am also truly grateful to my parents (Mr. Ja afar bin Mohd Tap and Mdm. Satariah binti Hasan), parents in-law (Mr. Md Said bin Ayob and Mdm. Zaleha binti Mohd) for their belief in me and their prayers during my doctoral journey. To my siblings, the support and the prayers will never be paid by me. I owed thanks to a very special person, my beloved and understanding husband Mr. Mohd Amir Nurasyid bin Md Said for his unconditional support through the thick and thin and also to my beloved and pretty daughter, Zara Sophea binti Mohd Amir Nurasyid, I would like to express my thanks for being such a good girl always cheering me up. Words would never say how grateful I am to both of you. I consider myself the luckiest in the world to have such a lovely and caring family, standing beside me with their love and unconditional support. v

7 TABLE OF CONTENTS CONFIRMATION BY PANEL OF EXAMINERS AUTHOR S DECLARATION ABSTRACT ACKNOWLEGMENT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS LIST OF ABBREVIATIONS Page ii iii iv v vi x xi xix xx CHAPTER ONE: INTRODUCTION Research Background Problem Statement Objectives Scope of Work Thesis Organization 7 CHAPTER TWO : BACKGROUND AND LITERATURE REVIEW Introduction Fundamental of Plasma Ionization Process In Plasma Medium Method of Generating Plasma Electrode Discharge Tube Plasma Generated by Using DC and AC Electrode-less Discharge Tube Capacitively Discharge Plasma(CDP) Inductively Coupled Plasma (ICP) Microwave Plasma Radio Frequency (RF) Plasma 25 vi

8 Laser Plasma Antenna Technology Coupling Technique Shape of Plasma Antenna Reconfigurable Plasma Antenna Summary 44 CHAPTER THREE: RESEARCH METHODOLOGY Introduction Research Methodology Fundamentals Parameters of Plasma Physics for Plasma Antenna Plasma Frequency Plasma Collision Frequency Conductivity of the Plasma Medium Complex Dielectric Permittivity of the Plasma Medium Estimation of Plasma and Collision Frequency Drude Dispersion Model for Designing Plasma Fabrication and Measurement Setup Fabrication Process Cylindrical Monopole Plasma Antenna Using Electrode-Less 65 Discharge Tube Monopole Plasma Antenna using Fluorescent Tube Reconfigurable Plasma Antenna Array Measurement Setup Return Loss Measurement Radiation Pattern Measurement Radiation Signal Measurement Measurement of Radiation Signal from Monopole Plasma 77 Antenna as a Transmitter Measurement of Radiation Signal from Monopole Plasma 77 Antenna as a Receiver Measurement of Signal Strength Monopole Plasma Antenna 78 vii

9 3.7 Summary 78 CHAPTER FOUR: A CHARACTERISTIC OF CYLINDRICAL MONOPOLE PLASMA ANTENNA Introduction Electrode-Less Discharge For Dielectric Barrier Discharge Design of Cylindrical Monopole Plasma Antenna Design Procedure Structure of Cylindrical Monopole Plasma Antenna Analysis of Cylindrical Monopole Plasma Antenna Effect of Plasma Frequency on Complex Permittivity Effect of Different Pressure Argon Gas Neon Gas Hg-Ar Gas Comparison of Different Gas Performance Results and Discussion Summary 104 CHAPTER FIVE: DEVELOPMENT MONOPOLE PLASMA ANTENNA USING FLUORESCENT TUBE FOR WIRELESS TRANSMISSION Introduction Mercury Argon (Hg-Ar) Fluorescent Lamp Parameter Study On A Monopole Plasma Antenna Using Fluorescent Tube Effects of the Length of Monopole Plasma Antenna Effects of Diameter Plasma Antenna Effects of Parameter for Coupling Sleeve Analysis Between Monopole Plasma Antenna and Metal Antenna Simulation and Measurement Results Wireless Signal Transmission Experiment Experiment Radiation Signal Monopole Plasma Antenna as a Transmitter 121 viii

10 5.6.3 Monopole Plasma Antenna as a Receiver Signal Strength for Monopole Plasma Antenna Summary 124 CHAPTER SIX: DEVELOPMENT OF RECONFIGURABLE PLASMA ANTENNA ARRAY Introduction Reconfigurable Plasma Antenna Array Reconfigurable Plasma Antenna Array Structure Analysis of Reconfigurable Plasma Antenna Array Effect of Distance Between Monopole Antenna to Fluorescent 129 Tube,D BB Effect of Thickness of Ground,t Effect of Length of Monopole Antenna,L M Effect of Numbers of Fluorescent Tubes and Adjacent Angle,θ Effect of Fluorescent Tubes on Radiation Pattern Switching Pattern of Reconfigurable Plasma Antenna Array for Beam 136 Scanning 6.5 Simulation and Measurement Results of Reconfigurable Plasma Antenna 145 Array 6.6 Summary 154 CHAPTER SEVEN : CONCLUSION, FUTURE WORKS AND RESEARCH CONTRIBUTION Conclusion Future Works Different Types of Gases Operating Frequency Different Shape of Plasma Antenna Research Contribution 158 REFRENCES 160 APPENDICES 171 AUTHOR S PROFILE 198 ix

11 LIST OF TABLES Tables Title Page Table 2.1 Types of electrode less discharge lamps and their applications 19 Table 4.1 The parameters of a monopole plasma antenna 83 Table 4.2 The performance of cylindrical monopole plasma antenna using 89 argon gas Table 4.3 The performance of cylindrical monopole plasma antenna using 92 neon gas Table 4.4 The performance of monopole plasma antenna using Hg-Ar gas 94 Table 4.5 The performance of monopole plasma antenna for different gases 99 at pressure 0.5 Torr Table 4.6 The performance of monopole plasma antenna for different gases 99 at pressure 5 Torr Table 4.7 The performance of monopole plasma antenna for different gases 100 at pressure 15 Torr Table 5.1 Optimized parameters for monopole plasma antenna 110 Table 5.2 Summary results signal strength for three conditions 120 Table 6.1 Optimized reconfigurable plasma antenna array specifications 129 Table 6.2 The performances analysis of the number of element and the angle between two adjacent elements 134 Table 6.3 Summary of switching pattern of reconfigurable plasma antenna 141 array for beam scanning Table 6.4 Switching setting for reconfigurable plasma antenna array (Blue 141 color represent activated elements ( switched ON), while white color represent deactivated elements (switched OFF)) Table 6.5 Simulated Radiation Characteristics of reconfigurable plasma antenna array 151 x

12 LIST OF FIGURES Figures Title Page Figure 2.1 Change in state of matter 11 Figure 2.2 Ionization process 11 Figure 2.3 Ionized plasma at loop antenna 12 Figure 2.4 Range of electron temperature and electron density for typical 13 plasma found in nature and in technological applications Figure 2.5 A schematic diagram for electrode discharge tube 14 Figure 2.6 (a) The schematic diagram of plasma antenna (b) the real 15 prototype for plasma antenna Figure 2.7 (a) The gain versus frequency curve of metal (b) The gain 15 versus frequency Neon plasma antenna Figure 2.8 The radiation pattern of metal antenna at 8.2 GHz (b) The 16 radiation pattern of Neon plasma antenna Figure 2.9 The plasma antenna construction 17 Figure 2.10 Measurement of return loss during switch off mode marked as 17 curve A and switch on mode marked as curve B and C Figure 2.11 Monopole plasma antenna radiation pattern at 590 MHz. Array 18 1(red line) is the co-polarization and Array 2(blue line) is the cross polarization Figure V AC-driven plasma antenna 18 Figure 2.13 The common diagram of BDB 20 Figure 2.14 Schematic diagram of the DBD plasma setup. A pair of 21 circular aluminum plate electrodes was covered with quartz glasses Figure 2.15 Typical capacitively coupled RF plasma reactor 21 Figure 2.16 The Schematic diagram of experimental apparatus of CCP. 22 Figure 2.17 Plasma formation by using ICP method 22 Figure 2.18 Schematic diagram to generate plasma 23 xi

13 Figure 2.19 Plasma column generate using microwave plasma 24 Figure 2.20 Longitudinal section of the surfaguide. The vertical tube contains plasma to be ignited 24 Figure 2.21 Experiment set up for plasma antenna 25 Figure 2.22 The monopole plasma antenna 26 Figure 2.23 Schematic of plasma antenna 26 Figure 2.24 The radiation pattern for copper metal antenna (b) The radiation pattern for plasma antenna 27 Figure 2.25 Schematic diagram of the RF propagation experiment 28 Figure 2.26 Schematic diagram for a proposed Beverage Antenna 28 Figure 2.27 Plasma antenna using coupling technique 29 Figure 2.28 Figure 2.29 Plasma antenna (a) Using a standard U-shape fluorescent lamp (b) coupling sleeve Coupling structures (a) Inductive coupling (b) Double inductive coupling (c) Capacitive coupling Figure 2.30 Block diagram of the plasma antenna circuit and measurements systems 31 Figure 2.31 Transmission characteristics (S21) for two type of coupling structures with different configurations 32 Figure 2.32 Coupling sleeve in an excitation box 33 Figure 2.33 Coupling between the two ports with (black) and without (gray) the conducting medium 33 Figure 2.34 Reflection coefficient of the signal port with (black) and 33 without (gray) the plasma Figure 2.35 Three different kinds of couplers (a) Solenoid Coupling (b) 34 Cubic coupling (c) Cylindrical coupling Figure 2.36 The ideal model of plasma helix antenna 35 Figure 2.37 Comparison results for radiation pattern between metal 36 antenna and plasma helix antenna (a) Horizontal plane (b) vertical plane Figure 2.38 Return loss, S 11 of plasma helix antenna 36 xii

14 Figure 2.39 A model of a plasma whip antenna located on dielectric 36 substrate with relative permittivity of 2.35 and the thickness, h is 2 mm Figure 2.40 Comparison results of return loss between plasma whip 37 antenna and metal antenna Figure 2.41 A plasma triangular monopole antenna 38 Figure 2.42 Plasma antenna (a) Single plasma antenna (b) Array plasma 39 antenna Figure 2.43 Comparison between normalized elevation radiation patterns 39 of single and array plasma antenna Figure 2.44 The schematic diagram of plasma antenna 40 Figure 2.45 The helical plasma antenna 40 Figure 2.46 The diagram of experimental setup 41 Figure 2.47 (a) The plasma column when driven power is 15 W (b) The 41 plasma column when driven power is 39 W Figure 2.48 Plasma reflector antenna installed in anechoic chamber 42 Figure 2.49 Radiation Patterns of Plasma Reflector Antenna and Metal 42 Reflector Antenna Figure 2.50 Geometry of reconfigurable plasma corner reflector antenna 43 Figure 2.51 The 24 plasma elements for reconfigurable plasma corner 43 reflector antenna with a monopole antenna in the center of the ground plane. Figure 2.52 Normalized H-plane radiation patterns, (a) Simulation. (b) 44 Measurement Figure 3.1 Flow chart of the research (a) Cylindrical monopole plasma 49 antenna (b) Monopole plasma antenna using fluorescent lamp and (c) Reconfigurable plasma antenna array Figure 3.2 Flow diagram of GLOMAC to calculate electron density for 61 argon and neon gases Figure 3.3 Flow diagram of GLOMAC to calculate electron density for 62 mixture of argon and mercury vapor Figure 3.4 Defining a plasma in CST 64 Figure 3.5 Monopole plasma antenna using electrode-less discharge tube 67 xiii

15 (a) schematic diagram (b) construction of monopole plasma antenna Figure 3.6 Photograph of neon gas discharge tube at 15 Torr 67 Figure 3.7 Photograph of argon gas discharge tube at 15 Torr 68 Figure 3.8 Position of coupling sleeve 69 Figure 3.9 Monopole plasma antenna using fluorescent tube (a) 69 Schematic diagram (b) Construction monopole plasma antenna Figure 3.10 Monopole plasma antenna integrated with 3G Wi-Fi router. 70 Figure 3.11 Monopole plasma antenna integrated with 3G Wi-Fi router 70 during switch ON Figure 3.12 Geometry of reconfigurable plasma antenna array (a) Side 71 view (b) Top view Figure 3.13 Prototype of reconfigurable plasma antenna array (a) 3D 72 AutoCAD drawing (b) Connection of 1 of fluorescent tube (c) Prototype of reconfigurable plasma antenna array Figure 3.14 Setup for return loss measurement 73 Figure 3.15 The radiation patterns measurement setup. The actual inside 74 view of the anechoic chamber room Figure 3.16 The radiation patterns measurement setup. Equipment for 75 radiation patterns measurement Figure 3.17 The layout of the measurement setup for radiation pattern 75 measurement Figure 3.18 Coupling sleeve is wrapping with aluminum shielding box (a) 76 left view (b) right view (c) bottom view (d) top view Figure 3.19 Coupling sleeve is wrapping with aluminum shielding box (a) 76 Front view during fluorescent tube switched OFF (b) Front view during fluorescent tube switched ON Figure 3.20 Experimental setup for plasma antenna that serves as a 77 transmitter Figure 3.21 Experimental setup for plasma antenna that serves as a receiver 77 Figure 3.22 Testing the signal strength of monopole plasma antenna 78 Figure 4.1 A simple schematic diagram of a capacitive discharge 82 Figure 4.2 The schematic diagram of discharge tube 83 xiv

16 Figure 4.3 Discharge tube used in this experiment 83 Figure 4.4 Relative Permittivity for argon gas, neon gas and Hg-Ar gas 85 for (a)0.5 Torr (b) 5 Torr and (c) 15 Torr Figure 4.5 The effect on reflection coefficient, S 11 for different pressure 87 for Argon gas Figure 4.6 The effect on VSWR for different pressure for Argon gas 88 Figure 4.7 Comparison of different pressure for Argon gas radiation 88 patterns in polar-plot Figure 4.8 The effect of reflection coefficient, S 11 for Neon gas at 90 different pressure Figure 4.9 The effect of VSWR for different pressure for Neon gas 90 Figure 4.10 Comparison of different pressure for Neon gas radiation 91 patterns in polar-plot Figure 4.11 The effect of reflection coefficient, S 11 for different pressure for 93 Hg-Ar gas Figure 4.12 The effect of VSWR for different pressure for Hg-Ar gas 93 Figure 4.13 Comparison of different pressure for Hg-Ar gas radiation 94 patterns in polar-plot Figure 4.14 The effect of reflection coefficient, S 11 for different gas at (a) Torr (b) 10 Torr and (c) 15 Torr Figure 4.15 Comparison of simulated VSWR for different gases at (a) Torr (b) 5 Torr and (c) 15 Torr Figure 4.16 The effect of radiation pattern in polar plot for different gas at 99 (a) 0.5 Torr (b) 10 Torr and (c) 15 Torr Figure 4.17 Simulated and measured reflection coefficient, S 11 of cylindrical 101 monopole plasma antenna. (a) Argon gas at 0.5 Torr. (b) Neon gas at 0.5 Torr. (c) Hg-Ar gas at 0.6 Torr. Figure 4.18 Simulated and measured radiation patterns. (a) At frequency GHz Argon gas in H-plane (left) and in E-plane (right). (b) At frequency 4.6 GHz Neon gas in H-plane (left) and in E-plane (right). (c) At frequency 4.5 GHz for Hg-Ar gas in H-plane (left) and in E- plane (right). Figure 5.1 Construction of the Fluorescent Lamp 108 xv

17 Figure 5.2 The structure of a monopole plasma antenna 109 Figure 5.3 The effects on reflection coefficient, S 11 due to change of 111 length monopole plasma antenna Figure 5.4 The effects on reflection coefficient, S 11 due to change of the 112 diameter of plasma antenna Figure 5.5 Coupling sleeve structure 113 Figure 5.6 Effects on reflection coefficient of parameter for coupling 113 sleeve. (a) Numbers of turns (b) Width of aluminum tape (c) Position of coupling sleeve (d) Diameter of coil (e) Distance between SMA connector to coupling sleeve Figure 5.7 Comparison of simulation results of reflection coefficient,s between metal antenna, condition during plasma OFF and ON Figure 5.8 VSWR for plasma antenna on, off and metal antenna 116 Figure 5.9 Simulated radiation patterns of plasma monopole antenna during ON,OFF and metal antenna in polar plots in the E-plane (phi = 90 ) 117 Figure 5.10 Simulated and measured reflection coefficient,s 11 for 118 monopole plasma antenna Figure 5.11 Simulated and measured radiation patterns of monopole plasma 119 antenna (ON) at 2.4 GHz in (a) H-Plane and (b) E-Plane. Figure 5.12 Captured signal when plasma antenna serves as transmitter 121 Figure 5.13 Noise floor when the RF generator is turned off. 122 Figure 5.14 Captured signal when plasma antenna serves as receiver. 122 Figure 5.15 Noise floor when the plasma antenna was removed from the 123 receiver system. Figure 5.16 Performance of Signal Strength when the fluorescent tube 124 antenna was connected to the AP Router Figure 5.17 Performance of Signal Strength when fluorescent tube antenna 124 disconnected from AP Router Figure 6.1 Geometry of the reconfigurable plasma antenna array (a) top 128 view (b) side view (c) overall structure Figure 6.2 The effect of distance between monopole antenna to fluorescent tube 130 xvi

18 Figure 6.3 Comparison of simulated gains at frequency 2.4 GHz in H- 130 Plane Figure 6.4 Comparison of radiation patterns in polar-plot in H-plane 131 Figure 6.5 Effect on S 11 when t is varied 132 Figure 6.6 Effect on reflection coefficient, S 11 and resonant frequency 132 when L M is varied Figure 6.7 Relationship between the number of fluorescent tubes and 133 adjacent angle. (a) 10 fluorescent tubes were used with only 6 elements activated (b) 12 fluorescent tubes were used with only 7 elements activated (c) 20 fluorescent tubes were used with only 15 elements activated. Figure 6.8 Simulated radiation pattern in polar plot in (a) E-Plane and (b) H- 133 plane. Figure 6.9 Simulation reflection coefficient,s Figure 6.10 Simulation and measurement results for radiation pattern in H-plane 135 (right) and E-plane (left). (a) Plasma off. (b) Monopole antenna only. Figure 6.11 Comparison between monopole and plasma off for simulation 136 results gain (db) versus frequency (GHz) Figure 6.12 Switching numbering for reconfigurable plasma antenna array 137 Figure 6.13 Simulated reflection coefficients, S 11 for switching pattern of 138 reconfigurable plasma antenna array Figure 6.14 Measured reflection coefficients, S 11 for switching pattern of 138 plasma antenna array Figure 6.15 Simulated radiation pattern at 2.4 GHz for switching pattern of 139 reconfigurable plasma antenna array (a) in H-plane and (b) in E- plane. Figure 6.16 Measured radiation pattern at 2.4 GHz for switching pattern of 139 reconfigurable plasma antenna array (a) in H-plane and (b) in E- plane. Figure 6.17 Simulated result for different number of elements in H-plane 140 (ϕ =50 ) (a) Gain in db (b) Directivity in dbi. Figure 6.18 Remote control and receiver 143 xvii

19 Figure 6.19 Photograph of the overall structure of reconfigurable plasma 144 antenna array integrated with Arduino technology Figure 6.20 Remote control with the main components 144 Figure 6.21 (a) Circuit at the remote control (b) Circuit at the receiver 145 Figure 6.22 Schematic drawing of reconfigurable plasma antenna array (a) 146 overall view (b) side view Figure 6.23 Prototype of the reconfigurable plasma antenna arrays (a) Deactivated 146 (Plasma off) of 12 fluorescent tubes. (b) 5/12 plasma in ON condition Figure 6.24 Simulated of reflection coefficient,s Figure 6.25 Simulated results of radiation pattern for reconfigurable 147 plasma antenna array at different switch configuration modes. Figure 6.26 Combination of simulated scanning radiation patterns in the H- 150 plane for reconfigurable plasma antenna array Figure 6.27 Simulated peak gains (abs) of reconfigurable plasma antenna 150 array with different main lobe directions at frequency 2.4 GHz Figure 6.28 Reflection coefficient, S 11 (a) Measurement (b) Simulation 151 Figure 6.29 Simulated and measured radiation pattern in H-plane at frequency 2.4 GHz 152 xviii

20 LIST OF SYMBOLS Symbols c λ J θ ρ σ S 11 Speed of light Permittivity Permittivity of free space Complex permittivity Relative dielectric constant at infinity frequency Wavelength Current density Electron mass Electron density Adjacent angle Charge density Electron charge Plasma frequency Electromagnetic wave frequency Plasma conductivity Antenna reflection coefficient/s-parameter Collision frequency Cathode fall voltage xix

21 LIST OF ABBREVIATIONS Abbreviations AC AP Ar 2 AUT CCP CDP CST DBD DC EMI ev FM HF HFSS Hg-Ar HPBW H 2 0 ICP MP Ne 2 PC RF SMA Tx UHF UV VHF VNA VSWR Alternating current Access point Argon gas Antenna under test Capacitively coupled plasma Capacitively discharge plasma Computer Simulation Technology Dielectric barrier discharge Direct current Electromagnetic interference Electron volts Frequency modulation High frequency High Frequency Structural Simulator Mixture of mercury vapor and argon gas Half power beamwidth Water Inductively coupled plasma Microwave plasma Neon gas Positive column Radio frequency SubMiniature version A Transmitter Ultra High Frequency Ultra Violet Very High Frequency Vector Network Analyzer Voltage Standing Wave Ratio xx

22 xxi

23 CHAPTER ONE INTRODUCTION 1.1 RESEARCH BACKGROUND In recent years, the current electronic communications industry has required high performance and efficient systems to meet the demands of the present continuously evolving applications. Nevertheless, physical limitations of microwave devices and circuits have stalled further improvements of the current technology. Besides, the rapid advances in technology have also significantly resulted in high demand for multi-function devices, including the antennas. Therefore, to cope with this demand, multi-function antennas can be considered as one of the key advances in future wireless communications technology. However, the development of these antennas has posed significant challenges to antenna designers particularly. In the midst of this scenario, the usage of plasma as a conductive element in microwave devices has drawn growing interest due to their peculiar and innovative properties with respect to the traditional metallic circuits. At present, the industrial potential of plasma technology is well-known and has been excellently demonstrated in several processes of microwave technology, which incorporates the use of an ionized medium. The term plasma is often referred to as the fourth state of matter. As the temperature increases, molecules become more energetic and transform in the sequence of solid to liquid to gas and plasma. The existence of plasma was first discovered by Sir William Crookes in In 1919, the concept of plasma antenna was patented and the patent was awarded to J. Hettinger with the name of "Aerial conductor for wireless signaling and other purposes" [1]. Besides, applications of plasma find wider use in our technology every day. From huge and sophisticated projects of fusion to material processing to simple lighting equipment, the plasma research is one of the most generously funded research topics. On many of the plasma applications, the plasma is generated, heated or manipulated by RF radiation [2]. The plasma is a state of matter in which charged particles such as electrons and atom nuclei have sufficiently high energy to move freely, rather than be 1

24 bound in atoms as in ordinary matter. Some examples of plasma are the fluorescent lighting tubes, lightning, and ionosphere. Furthermore, due to the unique characteristic of plasma which can be a conductor, it can be combined with antenna concepts and hence, make plasma antennas. Plasma antenna is a type of radio antenna that represents the use of ionized gas as a conducting medium instead of metal conductors to either transmit or receiver the radio frequency signal [3]. Recently, there has been a resurgence of interest in plasma antenna technology. The plasma is rapidly created and destroyed with applying proper radio frequency (RF) power pulses to the discharge tube so that the antenna is switched on and off. When the antenna is off, the plasma is non-conducting, and therefore the tube is practically transparent and behaves like a dielectric material, whereas when the plasma is on, it exhibits high conductivity, providing a conducting medium for the applied RF signal [4-5]. Thus the advantage in using plasma antennas instead of conventional antenna is that they allow an electrical rather than physical control. In particular, for military applications, when a plasma antenna is off ( not energized) it is difficult to detect with a hostile radar if its tube is properly designed compared to the conventional antenna due to material effect. This is because when a plasma element is not energized, it is transparent to the transmission above the plasma frequency, which falls in the microwave region [6]. Besides, by using plasma antenna in military application, it can reduce the usage of multiple antennas as well. The ability plasma antenna to be dynamically tuned and reconfigured for frequency, direction, bandwidth, gain and beamwidth in a single antenna could help the system in military to suite its requirement variation and to stay dependable [7]. On top of that, plasma element can also be applied as an antenna element for conventional communication systems. Since plasma is highly reconfigurable, the unused elements do not cause any unwanted effect to the whole systems. Besides, the implementation of plasma antenna enables the communication system to adjust its radio performances in order to suite and meet the changing of system requirement due to the system itself or due to environmental requirement. In addition, the communication systems at present have become more complex especially to cope with the increasing number of users. Therefore with the ability of plasma, the communication systems are capable to remain reliable over time. 2

25 The research contributions in this thesis describe the concept of plasma antenna and beam switching using plasma element for communication application. There are three types antenna structures were designed in this research work: first design is cylindrical monopole plasma antenna using discharge tube, second design is monopole plasma antenna using fluorescent tube and third design is the reconfigurable plasma antenna array using fluorescent tube. The coupling technique was used in designing the cylindrical monopole plasma antenna and the monopole plasma antenna using fluorescent tube. In the cylindrical monopole plasma antenna, the interaction between the plasma element and the electromagnetic wave was investigated.the effects of plasma parameters, such as the different gases and the varying pressures to the performances of the antenna, were investigate and are presented in chapter four. In this model, the dielectric barrier charge was used to generate the plasma. Besides, three different gases were analyzed which were argon gas, neon gas and Hg-Ar gas with pressures 0.5 Torr, 5 Torr and 15 Torr respectively. Meanwhile, the monopole plasma antenna using fluorescent tube and the reconfigurable plasma antenna array using fluorescent tube were designed based on commercial fluorescent lamp in the market. The monopole plasma antenna using fluorescent tube and reconfigurable plasma antenna array using fluorescent tube were designed at a target frequency of 2.4 GHz which was suitable for wireless application. In monopole plasma antenna using fluorescent tube a fluorescent tube with a length of mm and diameter 28 mm was used as a plasma antenna. The result from the monopole plasma antenna using fluorescent tube showed that fluorescent tube could be applied as a plasma antenna, and therefore, it proved that the commercial fluorescent lamp possessed the potential to be used as a good conductor element and also a low cost plasma antenna. Thus the next design still applied the commercial fluorescent tube in this research. In reconfigurable plasma antenna array using fluorescent tube, the concepts of reconfigurable and beam steering were implement to design this antenna. By using the special properties of plasma, which can be rapidly activated (switch ON) and de-activated (switch OFF) in few seconds, the concept of reconfigurable radiation pattern was applied in this research. Besides, with the implementation of reconfigurable plasma antenna array on a single ground plane, the radiation pattern was enabled to reconfigure over 12 directions to be 3

26 realized just at fingertips. Hence, the relationship between the plasma element and the radiation characteristic were investigated in this work. Apart from that, the reconfigurable plasma antenna array had been a reconfigurable antenna with a combination of monopole antenna and fluorescent tube function as a plasma medium to produce beam steering control. In contrast to conventional antennas that produce fixed directional radiation patterns, the reconfigurable plasma antenna array structure is capable of scanning the beam pattern over 360.Simulated and measured results of tests on the three antennas are presented and were compared to demonstrate the performance of the proposed antennas. These results confirmed that the main beam directions could be pointed to the desired direction by controlling the switches. Moreover, the direction of beam pattern could rapidly change within split seconds with a fast switching scheme. In fact, the fastest time taken to change the beam pattern direction depended only on the time taken by the plasma to decay. In addition, the entire switch configuration modes in all antennas design were controlled by an Arduino microcontroller. Arduino can control the switching of the plasma antenna whereby the users can control the ON and OFF of the fluorescent lamp with remote control. Hence, the development of Arduino microcontroller was programmed using the Arduino technology software. In the Antenna Research Group (ARG), Universiti Teknologi MARA (UiTM) Malaysia, this research had been one of the earliest works that dealt with plasma antenna. Therefore, at this moment, this study is indeed very important since it would become a starting point in the ARG so that other works will benefit from the output of this work. 1.2 PROBLEM STATEMENT The industrial potential of plasma technology is well known and has been excellently demonstrated in several processes of microwave technology, which incorporates some uses of an ionized medium. Nevertheless, despite of the numerous advantages, the construction of a plasma based radiating element requires trial-anderror experimental works due to lack of in-depth study on the fundamental mechanism of plasma radiation itself. Thus, rigorous investigation on the physical interaction mechanism between electromagnetic field and plasma had been necessary. The best 4

27 available option was to use computer (numerical) models of plasma antennas. Therefore, there had been a need for computer (numerical) modeling to analysis the characteristics of antennas, as well as to verify the parameters for future studies. Besides, progress in the technology of wireless communication systems has created a strong need for the development of new antenna structures. In wireless communication systems, a conventional antenna is capable of producing only a fixed directional radiation pattern [8]. This is not the case when using reconfigurable antennas which can change the direction of the main lobe of a radiation pattern for modern wireless communications. Moreover, reconfigurable antennas make it possible for use of a single antenna for multiple applications. However, physical limitations of the conventional antennas limit the dynamic range of beam steering due to interelement coupling effects and co-site interference [8 10]. On top of that, the antenna technology has been widely use in military application. In fact, several papers have looked into antenna technology in military application using conventional antenna [12 15]. However, the radar could detect the conventional antenna due to the material antenna. Hence, it is very important to design an antenna with good safety factor to avoid usage of antenna in military application being discovered by the enemy. Nowadays, the demand for modern and smart application in wireless technology is rather high. The proper installment of a complete set of Wi-Fi systems in the house or any indoor applications by using conventional metal antenna has specific space constraint as the antenna is required to be placed at particular areas to allow efficient coverage and signal. The unsuitable placing area makes the installment parts of conventional metal antenna highly visible to others. However, this can be eliminated by using plasma antenna technology. Plasma antenna is one of the camouflage technologies that have streamline appearance in the space of an area. In plasma antenna, by using commercial fluorescent lamp as a plasma medium, the antenna possesses dual function at one time. Besides operating as a lighting source, the plasma antenna using fluorescent lamp can serve as a Wi-Fi system, whereby the lamp functions as an antenna at the same time. 5

28 1.3 OBJECTIVE OF THE RESEARCH This research has beneficial implications for communication systems environments. The development of antennas by using plasma medium instead of metal element is definitely a good improvement in the antenna technology. This research involved antenna design simulations, fabrications, and measurements in order to develop the best possible types of antennas. Hence, the research was embarked based on the following objectives: 1. To analyze and investigate the relationship between plasma behaviors with RF characteristic. 2. To design and conduct experiment interaction between plasma element and RF microwave with three types of gases which is argon gas, neon gas and Hg-Ar gas (a mixture of mercury vapor and argon gas), as well as with pressures 0.5 Torr, 5 Torr and 15 Torr. 3. To design and develop plasma antenna as a radiating element by using commercial fluorescent lamp for Wi-Fi application. 4. To design and develop a reconfigurable antenna by using plasma element with capabilities of beam scanning and beam shaping. 5. To design and construct a microcontroller circuit with Arduino system, as well as to implement it to a reconfigurable antenna. The reconfigurable antenna by using plasma as its medium structure should be capable of scanning the beam pattern over SCOPE OF WORK The main emphasis of this research was to design and to develop plasma antennas based on plasma medium. In order to achieve that, the research had been divided into two; software and hardware parts. The software part included the antenna design process, its simulations, and also the switching circuit network design. Meanwhile, the hardware part included the fabrication of the proposed antenna. 6

29 In order to start, a comprehensive review was required to obtain knowledge on antenna design. The proposed antennas were designed and simulated using Computer Simulation Technology (CST) Microwave Studio. Besides, to calculate the plasma parameter such as plasma frequency and plasma density, GLOMAC simulation was employed. GLOMAC is a computer code for describing low pressure gas such as electron density and electron temperature. In the other hand, switching circuit network was designed using Arduino. Arduino is a single-board microcontroller, intended to make building interactive objects or environments more accessible. The design parameters of both designs were optimized to achieve, optimal results. After satisfied results from the simulation were obtained, the prototype antennas were fabricated and tested. The measurement of antenna reflection coefficient and radiation pattern was carried out using Vector Network Analyzer (VNA) and spectrum analyzer at anechoic chamber. Finally, the comparisons were made between simulation and measurement results then analyzed and documented. 1.5 THESIS ORGANIZATION The above serves as a general introduction to the background of this study and its significances. The problem statements and research questions are also included. In addition, the objectives of this study and the scope of work are also noted. Chapter Two describes the literature review for this study. Review of previous studies and an overview of plasma antennas, as well as the behavior of plasma medium are covered. Literatures on plasma antenna technology and reconfigurable plasma antenna are also included. Chapter Three provides the methodology of this study including the basic antenna design structure and the theoretical concept of the antenna in plasma medium. The method to determine plasma parameter such as plasma density is also presented. Chapter Four describes an analysis of plasma antenna characteristics by using discharge tube for different gases. In this chapter, three types of gases which are argon gas, neon gas and Hg-Ar gas are presented. Different gas pressure settings were used for different types of analyses. The simulation had been based on the varying gas pressure settings at 0.5 Torr, 10 Torr and 15 Torr for the three types of gases, while in experimental the analysis was carried out with sets of gas setting pressure only 7

30 applicable to argon gas and neon gas, as the Hg-Ar gas was used based on its standard manufacturing gas pressure. Besides, the results of the comparative analysis, along with discussions, are also included. Chapter Five explains the design and the development of the monopole plasma antenna by using fluorescent lamp at 2.4 GHz for Wi-Fi application. The analysis of monopole plasma antenna parameter is also presented. Thereafter, comparisons and discussions between simulation and measurement are covered based on the results. Chapter Six presents the reconfigurable plasma antenna array. A reconfigurable plasma antenna was constructed in this research works capable operate at frequency 2.4 GHz. The design and the optimization are thoroughly explained within the chapter. In addition, the analysis of reconfigurable plasma antenna array is also presented while the simulation results are compared with the measurement results. Lastly, Chapter Seven in which some ideas for improvement and possible areas for future research work and also research contribution are presented. 8

31 CHAPTER TWO BACKGROUND AND LITERITURE REVIEW 2.1 INTRODUCTION Plasma physics is a rapidly expanding field of science. For a long time, it has coincided with the field of electrical discharges in gases but recently, new fields of application of plasma physics have appeared. Vital to antenna technology, plasmas are conductive assemblies of charged and neutral particles and fields that exhibit collective effects. Besides, plasmas carry electrical currents and generate magnetic fields. Moreover, combining plasma and antenna in one system is interesting in the antenna technology. A plasma antenna is a type of antenna in which the metalconducting elements of a conventional antenna are replaced by plasma element. This types of radio antennas that employ plasma element as a radiator for electromagnetic radiation. Besides, plasma antennas are interpreted as various devices in which plasma with electric conductivity serves as an emitting element. In plasma antenna the concept is to use plasma discharge tubes as the antenna elements. When the tubes are energized, these turn into conductors, and can transmit and receive radio signals. When de-energized, these revert to non-conducting elements and do not reflect probing radio signals [16]. This chapter will explain briefly on the overview of plasma antenna. In section 2.2, the fundamental of plasma is covered, and followed by the elementary process in ionization plasma medium in section 2.3. Next is the method of generating plasma whereby in this section, divided into two section methods of producing plasma using electrode and electrode-less. In section 2.5, previous studies and clarification on plasma antenna technology are explained. This section reviews the previous researches used for coupling technique in plasma antenna. Meanwhile, the next section of this chapter explains the shape of plasma antenna and followed by reconfigurable plasma antenna. Finally, the last section in this chapter depicts the summary of the application of plasma in antenna technology. 9

32 2.2 FUNDAMENTAL OF PLASMA First and foremost, plasma is an ionized gas. Hence, it consists of positive (and negative) ions and electrons, as well as neutral species. The term plasma is used to describe a wide variety of macroscopically neutral substances containing many interacting free electrons and ionized atoms or molecules, which exhibit collective behavior due to the long-range Coulomb forces. In fact, the word plasma derived from the Greek and it means something molded. It was applied for the first time by Tonks and Langmuir in 1929, to describe the inner region, remote from the boundaries of a glowing ionized gas produced by electrical discharge in a tube [17]. When a solid is heated sufficiently until the thermal motion of the atoms breaks the crystal lattice structure apart; usually, a liquid is formed. When the liquid is heated enough until the atoms vaporize off the surface faster than they recondense, a gas is formed. Next, when the gas is heated enough that the atoms collide with each other and knock their electrons off in the process, plasma is formed, the so-called the fourth state of matter. Figure 2.1 illustrates the transformation process from solid to liquid, and next, transforms to gas, and lastly, plasma when heat is increased. Hence, to demonstrate the transformation towards the fourth state of matter is best described by taking water (H 2 O) as an example. Ice represents the solid state of H 2 O, in which the molecules of ice are fixed in lattice. The kinetic energy of each ice molecule is very weak, and therefore, the ice remains in a solid state unless extra energy is applied. If adequate energy is applied to the ice, the molecules will have more kinetic energy that allows them to agitate. The extra energy will also cause some of them to move freely. This condition turns the ice into water (liquid state). If more energy is applied to liquid, for example by boiling the water, the molecules will have more energy and get excited. As a result, the molecules are free to move and change into steam (gaseous phase). In this case, the spacing between each molecule is large enough compared to its previous states of matter. Since each molecule moves in a random manner, the kinetic energy for each molecule is different. If the steam is subjected to thermal heating, illuminated by UV or X-rays or bombardment by energetic particles, it becomes ionized. Plasma is not usually made simply by heating up a container of gas. Typically, in the laboratory, a small amount of gas is heated and ionized by driving an electric 10

33 current through it or by shining radio waves into it. Generally, these means of plasma formation give energy to free electrons in the plasma directly and then electron-atom collisions liberate more electrons and the process cascades until the desired degree of ionization is achieved. Figure 2.1 : Change in state of matter [18]. 2.3 IONIZATION PROCESS IN PLASMA MEDIUM Since the plasma is an ionized medium, the key process in plasma is the ionization process because it is responsible for plasma generation. The simplest of ionization process is illustrated in Figure 2.2. Figure 2.2 : Ionization process [19]. A normal atom is electrically neutral because it has the same number of electrons (particles bearing a negative charge) as protons (particles bearing a positive charge). Ionization is the process when normal atom becomes a negative ion (anion) by gaining one or more electrons, or it can become a positive ion (cation) by losing 11

34 one or more electrons. The process of ionization starts when a sufficiently high potential difference is applied between two electrodes, the neutral atom is accelerated by the electric field in front of the cathode and collides with the gas atoms. The gas atoms will break down and produce electron ions and positive ions. The ionization degree can vary from 100% (fully ionized gases) to low degree values (partially ionized). Figure 2.3 shows an example of ionization process in loop antenna. The plasma antenna fabricated in [20] is the loop discharge tube that contains a gas, and at the end of the tube, consists a pair of electrodes. When a gas is excited by applying sufficient voltage to the electrode, the neutral atom at the electrode will accelerate and collide with the gas atoms and produce electrons and positive ions, and thus, plasma formation begins. Figure 2.3: Ionized plasma at loop antenna [20]. Figure 2.4 shows of electron temperature in electronvolts,ev and electron densities in (1/m 3 ) for typical of natural and manmade plasmas. Most plasma for practical significance has electron temperature that ranges from 1 to 20eV with electron densities in the range from 10 6 to /m 3. 12

35 Figure 2.4 : Range of electron temperature and electron density for typical plasma found in nature and in technological applications [21]. 2.4 METHOD OF GENERATING PLASMA Plasmas can be generated through the application of electric and magnetic fields, RF heating and laser excitation. Meanwhile, plasma column can be generated by using such as DC, RF, laser and microwave. The gases that can be used to compose the plasma are neon, xenon, argon, krypton, hydrogen, helium and mercury vapor. In general, the formation of plasma can be divided into two groups by using electrode discharge tube and electrode-less discharge tube. Electrode discharge tube is a tube that contains gas-filled with the current injected at the electrode while electrode-less discharge tube is discharge that has no internal electrodes Electrode Discharges Tube Electrode discharge tube is a tube that contains a gas. It is a tube that employs an electric discharge through a gas as the means of converting electrical energy into light [16-22]. Figure 2.5 shows the schematic of electrode discharge tube. The two metal electrodes are cathode and anode. An anode is located at one end while cathode at the other end. The typically gas-filled in the tube is neon but other gases can also be used. 13

36 Figure 2.5: A schematic diagram for electrode discharge tube [23]. Plasma is formed when sufficient voltage is supplied between two metal electrodes in a glass that contains gas [23]. The basic operating mechanism is when an electric potential volt is applied between the two electrodes [24]. A few electrons are emitted from the electrodes due to the omnipresent cosmic radiation. Without applying a potential difference, the electrons emitted from the cathode are not able to sustain the discharge. However, when a potential difference is applied, the electrons are accelerated by the electric field in front of the cathode and collide with the gas atoms. The most important collisions are the inelastic collisions, leading to excitation and ionization. The excitation collisions, followed by de-excitations with the emission of radiation, are responsible for the characteristic name of the glow discharge. The ionization collisions create new electrons and ions. The ions are accelerated by the electric field toward the cathode, where they release new electrons by ion induced secondary electron emission. Besides, the electrons give rise to new ionization collisions, creating new ions and electrons. These processes of electron emission at the cathode and ionization in the plasma make the glow discharge self-sustaining plasma. The next section, presents the previous studies that applied electrode discharge tube by using DC and AC Plasma Generated by using DC and AC Plasma antenna is a general term that represents the use of plasma as a conductive medium to transmit or reflect signals. In previous studies, plasma antenna used 500 MHz 100 W RF power to generate a plasma column, which was limited in energy efficiency and bandwidth. In paper [25], the researcher implemented DC bias to generate plasma column as a conductive medium. This paper, which attempted to develop DC-biased plasma antenna, had no operation frequency for upper limit and had low sustaining power. Besides, the signal was coupled to the plasma antenna via capacitive coupling. 14

37 (a) (b) Figure 2.6 : (a) The schematic diagram of plasma antenna. (b) The real prototype for plasma antenna [25]. Figure 2.6 shows the schematic diagram and the real plasma antenna. In this work, two plasma antennas of 1m and 60 cm in length were built. The plasma antenna is constructed from 12 mm outer diameter 10 mm inner diameter glass tube, and inside was filled with Neon gas at 2~5 Torr. The discharge tube that had been fabricated on both sides of the tube had been two hollow cathode type cylindrical electrodes. At both electrodes, two wires for DC bias current were connected to a high voltage power supply. When first turned on, the applied voltage had to exceed the breakdown voltage of roughly 1.5 KV (for 1m antenna), then the discharge turned into current control mode at a fixed voltage drop of ~900V. The discharge current ranged from 5-30 ma at the same voltage drop. The diameter of the positive column was about 5 mm, whereas the plasma density in the tube was estimated to be about cm -3. (a) (b) Figure 2.7: (a) The gain versus frequency curve of metal. (b) The gain versus frequency Neon plasma antenna [25]. 15

38 (a) (b) Figure 2.8: (a) The radiation pattern of metal antenna at 8.2 GHz (b) The radiation pattern of Neon plasma antenna [25]. Figure 2.7 (a) illustrates the gain versus frequency graph for metal antenna, while figure 2.7(b) shows the gain versus frequency for Neon plasma antenna, at 8.2 GHz. The red curve represented co-polarization, whereas the green (blue) curve was cross polarization. From this graph, the metal antenna and the Neon plasma antenna exhibited the same general trend of rising gain after 8 GHz. Figure 2.8 shows the graph for radiation pattern of metal antenna and Neon plasma antenna at 8.2 GHz respectively. From this experiment, the radiation patterns of all three antennas were basically omni-directional. Usually a gas-filled dielectric tube used with electrode is operated on an AC supply which is known as fluorescent lamp. Due to its high performance in converting electrical power to light, size flexibility and good color rendering properties make them most successful lamp product. Paper [26] depicts a work on fluorescent tube that performed as a plasma antenna. The AC voltage was applied across the filaments present at both ends of a tube, and it provided an intense source of electrons. Argon gas was energized to the plasma state which excited Mercury vapor to radiate UV rays. The glow due to fluorescence indicated that the Argon gas inside the tube changed into plasma state and formed the plasma column. Figure 2.9 represents the plasma antenna by using fluorescent lamp. Figure 2.10 shows the results of return loss in switch on mode and switch off mode. In switch on mode, the two most different fluctuating results on network analyzer were identified, which explained the features of the antenna loss for fluorescent tube as plasma antenna as shown in Figure 2.10 through B and C curves 16

39 while during switch off mode, the results of return loss showed that there was no reflection and it means that the fluorescent tube could function as a plasma antenna. Figure 2.11 illustrates the result for radiation pattern for monopole plasma antenna. Figure 2.9: The plasma antenna construction [26]. Figure 2.10: Measurement of return loss during switch off mode marked as curve A and switch on mode marked as curve B and C [26]. 17

40 Figure 2.11: Monopole plasma antenna radiation pattern at 590 MHz. Array 1(red line) is the co-polarization and Array 2(blue line) is the cross polarization [30]. In paper [27], the plasma antenna used AC driven supply to produce plasma column. The experimental loop plasma antenna was a commercial annular fluorescent lamp with a dimension of 100cm in perimeter and 1cm in its cross sectional diameter. It contained about 0.03Pa of Hg and about 300Pa of Argon. Figure 2.12: 220V AC-driven plasma antenna [27]. 220VAC as well as RF source was fed through the electrodes. In order to eliminate the antenna effect of wires necessary for 220VAC feeding, ferrite chokes were employed. A 1:4 transmission line transformer was used as balun to connect the RF power generator to the antenna. The power scale of the RF generator was about 40W. The system with 220V AC source is depicted in Figure

41 2.4.2 Electrode-less Discharge Tube Meanwhile, an electrode-less discharge tube is a tube that has no internal electrodes. It was discovered by Hittorf [28] in 1884 and more complete observations were made soon after by Thomson [29] and Tesla [30]. Electrode-less discharge tube can be divided into three groups, Capacitively Discharge plasma (CDP), Inductively Coupled Plasma (ICP) and Microwave Plasma (MP). Table 2.1 shows a detailed classification of electrodeless lamp based on their discharge mechanism that has already been discussed in the previous section. Table 2.1 : Types of electrode less discharge lamps and their applications Electrode-less discharge type Power Application CDP 1W~1kW Fluorescent lamp Facsimile lamp Excimer lamp ICP 10W~1kW Fluorescent Lamp High power UV lamp Road lamp MP 1kW~ Photochemistry HID lamp Capacitively Discharge Plasma (CDP) Another method to generate plasma column by using electrode-less discharge tube is capacitively discharge plasma (CDP). CDP can be divided into two categories; Dielectric Barrier Discharge (DBD) and Capacitively Coupled Plasma (CCP). CDP discharges are widely used for dielectric etching in the semiconductor industry. Plasma-generation efficiency (i.e., electron density obtained for a given input power) improves in CDP with increasing frequency [31]. DBD is characterized by the presence of one or more insulating layers in the current path between metal electrode in addition to the discharge space [32]. A basic diagram of DBD is shown in Figure

42 Figure 2.13: The common diagram of BDB [32]. An experimental device for DBD generally consists of two parallel electrodes separated by thin dielectric layer. An AC voltage is applied to the electrodes at a frequency of several hundred hertz (Hz) to few hundred kilo hertz (khz). A breakdown occurs in the gap between the two electrodes at a sufficiently high voltage enough to ionize the media around. As the charges collect on the surface of the dielectric, they discharge in microseconds, leading to their reformation elsewhere on the surface. Plasma is sustained if the continuous energy source provides the required degree of ionization overcoming the recombination process leading to the extinction of the discharge. The discharge process causes the emission of an energetic photon, the frequency and energy of which corresponds to the type of gas used to fill the discharge gap. DBD devices can be made in many configurations, typically planar, using parallel plates separated by a dielectric or cylindrical; using coaxial plates with a dielectric tube between them. Common dielectric materials include glass, quartz, ceramics and polymers. The gap distance between electrodes varies considerably, from less than 0.1 mm in plasma displays, several millimeters in ozone generators and up to several centimeters in CO 2 lasers. The purpose of the dielectric barrier is to limit the electron current between the electrodes. In paper [33], the dielectric barrier discharge plasma was used to generate a stable strain of Klebsiella pneumonia (designated to as Kp-M2) with improved 1,3- propanediol production. The current study aimed to obtain more support for the positive effect induced by DBD plasma and to generate an excellent industrial strain of K. pneumoniae for accumulating 1,3-PD. As shown in Figure 2.14, DBD plasma in air at atmospheric pressure was generated at 20 khz and 24 kv between a pair of circular aluminum plate electrodes covered with quartz glasses. A discharge gap of 3 mm between the upper electrode and the surface of the sample suspension was selected. 20

43 Figure 2.14: Schematic diagram of the DBD plasma setup. A pair of circular aluminum plate electrodes was covered with quartz glasses [33]. Capacitively coupled plasma (CCP) is generated with high-frequency RF electric fields, typically MHz. A conventional RF system for sustaining a discharge consists of a generator and the reactor with electrodes as shown in Figure Figure 2.15: Typical capacitive coupled RF plasma reactor [34]. It essentially consists of two metal external electrodes separated by a small distance, placed in a reactor. One of the external electrodes is connected to the RF power supply, and the other one is grounded. As this configuration is similar to a capacitor in an electric circuit, the plasma formed in this configuration is called capacitively coupled plasma. CCPs are successfully applied for a wide range of applications such as deposition of thin-films, plasma etching and sputtering of insulating materials as well as micro fabrication of an integrated circuit manufacturing industries for plasma enhanced chemical vapor deposition (PECVD). In paper [34] presented the formation of plasma using CCP method. As illustrates in Figure 2.16, a RF power was supplied through a 52 mm diameter 21

44 stainless steel electrode in CCP configuration. Ring shaped Sm-Co magnets and cylindrical Sm-Co magnets were mounted in the electrode to form planar magnetron magnetic field geometry for effective production of high density plasma near the electrode. Figure 2.16: The Schematic diagram of experimental apparatus of CCP [34] Inductively Coupled Plasma (ICP) On the other hand, plasma can be formed by using method inductively coupled plasma. ICP is an electrode-less discharge where RF power is coupled to the plasma through a magnetic field. The standard frequency used is MHz. Figure 2.17: Plasma formation by using ICP method [23]. As shown in Figure 2.17 the plasma is induced by coupling the RF energy at MHz through a capacitive matching network. The RF current flowing in the coil generates an RF electric field which accelerates the free electrons causing ionization and producing the plasma [23]. The time varied magnetic field created by the primary induction coil which is placed outside the lamp maintains the plasma. 22

45 Microwave Plasma Plasmas that are created by injection of microwave power, i.e. electromagnetic radiation can be called as microwave induced plasmas. The microwave discharge plasma generated at low pressure has been used in many industrial productions such as semiconductor and optical component production as a device for etching or deposition, because it is clean and has high chemical reactivity. It is also being used as ion production, atomization and light, and excitation source in ion bombardment, nitrification and solar lamps as well as analytical chemistry, respectively. The plasma described in [35], uses a microwave plasma generation. In this paper, the authors developed a plasma source without electrodes. As shown in Figure 2.18, the microwave plasma torch consists of the same magnetrons used in typical home microwave ovens. The magnetrons used in this study were model number OM75A. They operated at a frequency of 2.45 GHz and their average power was about 1 kw. To plasma continuously generate the circuit was modified to full wave voltage doublers. From Figure 2.18 by injecting swirl gas, the plasma column inside the discharge tube was more stabilized. Figure 2.19 shows the plasma column when 30 lpm air was injected as a swirl gas. Figure 2.18 : Schematic diagram to generate plasma [35]. 23

46 Figure 2.19: Plasma column generate using microwave plasma [35]. Meanwhile, paper [36] proposed a new way of producing plasma column by using microwave and RF discharges based on electromagnetic surface waves to sustain the discharge. In this way plasma could be driven from only one end of the column and electrodes should no longer be needed. A plasma column was created by applying a pump signal to a tube containing a gas; the gas was ionized by a strong microwave electric field applied at one termination of the tube by a surfaguide device. The surfaguide launched an azimuthally symmetric electromagnetic surface wave that propagated along the tube creating and sustaining the plasma column [36]. Figure 2.20 illustrates the longitudinal section of the surfaguide. It consisted of two trunks L 0 of a standard waveguide WR340, two transitions L 1, and a waveguide L 2 with a reduced height. The guide was terminated by a moving short, whose length Ls could be varied for matching when the plasma column was turned on. Figure 2.20: Longitudinal section of the surfaguide. The vertical tube contains plasma to be ignited [36]. 24

47 Radio Frequency (RF) plasma Meanwhile, as for antenna applications, the plasma must be maintained in precise spatial distributions such as plasma column. The plasma volume can be contained in an enclosure (tube) or suspended in free space. Energizing the plasma column can be accomplished with RF heating, for instance. The paper reported in [37] presented plasma antenna by using 500 MHz adjustable power RF. Figure 2.21: Experiment set up for plasma antenna [37]. Figure 2.21 shows the experiment set up for plasma antenna. In this experiment the system mainly included tuner, power amplifiers, RF source, low-pass filter, power meter, HF/VHF transmitter, spectrum (noise, and network) analyzer. The gas filled in the electrode discharge tube was mercury steam and argon. The length was 1.3 m and the radius was 10 cm, while the coupling ring (used for sending and receiving signal) was fixed in 15 mm to the top and bottom, and are connected to RF drive pump. From this experiment, the plasma antenna had wider bandwidth compared to metal antenna with similar dimensions. Another plasma formation by using RF was developed in paper [26].In this work, monopole plasma antenna was excited by surface wave as shown in Figure 2.22 (a) and (b). 25

48 (a) (b) Figure 2.22: The monopole plasma antenna [26]. Figure 2.22 illustrates the experimental set up for monopole plasma antenna. The plasma was generated by using RF. In this experiment, the gas employed was hydrogen gas with plasma density estimate equal to cm -3. Besides, this paper analyzed three-dimensional distributions of electric and magnetic fields around the monopole plasma antenna. By using Maxwell-Boltzmann equation and applying molecular dynamic, the related formulas and equations of the model were obtained. The plasma antenna presented in paper [40] shows the plasma column formation using RF generator operated at a frequency of 3 MHz to 10 MHz and power up to 100 W. Figure 2.23: Schematic of plasma antenna [40]. Moreover, a schematic diagram of the experimental setup for generated plasma column was developed, as shown in Figure In this work, the discharge tube was 26

49 30 cm in length with a diameter 3 cm. The plasma antenna used argon gas as the plasma medium. Besides, a capacitive coupler width of 35 mm was mounted 2 mm above the ground plate. From this work, it found that the current on the surface of the antenna decreased along the axis of the antenna, but it increased with the working pressure at a particular position and constant input power. The plasma antenna efficiency was 35% in this experiment. The radiation pattern for plasma antenna and copper metal antenna was also compared and displayed similar pattern as shown in Figure 2.24 (a) and (b) respectively. (a) (b) Figure 2.24 : (a) The radiation pattern for copper metal antenna. (b) The radiation pattern for plasma antenna [40] Laser There are several approaches to creating a plasma antenna. Dwyer et al.[41]discussed and successful prove that the plasma produced by laser-guided in the atmosphere has been used as both a transmitting and a receiving antenna. In this experiment used either a CO 2 laser or a glass laser. From Figure 2.25, A 1 represents the plasma antenna being used as the transmitter. As shown in Figure 2.25, the laser from NL which is a glass laser. The laser passed through a long focal length lens which is representing L in Figure The laser was used to designate the path of the antenna while an electrical discharge is employed to create and sustain the plasma. But the laser generates a weakly ionized plasma column, which is then sustained by the discharge from a Marx generator with a maximum charge of 360 kv. The plasma produced by a laser-guided, electric discharge in the atmosphere has been formed in the shape of a folded monopole antenna with a characteristic frequency of 112 MHz. 27

50 This plasma antenna has been used to transmit and receive signals at 112 MHz. Researchers at the Naval Research Laboratory have also observed that electric discharges could be guided in abnormal paths through atmosphere to create desired antenna geometries through the use of lasers. Figure 2.25: Schematic diagram of the RF propagation experiment [33]. Another example of plasma generated by a laser is presented in [42]. In this research, a laser plasma filament was used to produce plasma column which could be used in passive radar application. Plasma filaments induced by laser would give propagation of high power femtosecond laser pulses in air and produced great interest, besides finding many applications in many fields [43]. Figure 2.26 show a virtual reconfigurable plasma antenna consisting of a set of laser plasma filaments produced in air by the propagation of femtosecond laser pulses in air. The generated plasma through filamentation was cold plasma, and thus, it could be suspended in free space to serve as an antenna [44]. To consider the plasma antenna to behave as an effective of metal antenna, the plasma frequency must greater than the operating frequency [2-37]. In this work, the plasma frequency is estimated around GHz. Thus it was better for plasma antenna to operate the frequency at about 30 GHz. Figure 2.26: Schematic diagram for a proposed Beverage Antenna [42]. 28

51 2.5 PLASMA ANTENNA TECHNOLOGY The concepts from the combination of plasma technology and antenna technology have become practical in recent years but the idea is not new. The history of using ionized gas as a transmitter and receiver was discovered by J.Hettinger in In his research he suggested that ionized gas (plasma) can be used to transmit and receive signal [1]. A plasma antenna is a type of radio antenna currently in development in which plasma is used instead of the metal elements of a traditional antenna. A plasma antenna can be used for both transmission and reception. Besides, plasma antenna has attractive features such as by using plasma antennas instead of metallic elements, they allow an electrical rather than physical control. However, the development of these antennas poses significant challenges to both antenna designers and system designers. In this section the overview of previous researches involving plasma antenna technology is discussed Coupling Technique In order the radiation signal to be transferred to plasma antenna, the signals should be connected to the tube with a coupler and it is called coupling sleeve. Figure 2.27 shows an example coupling sleeve. Figure 2.27 :Plasma antenna using coupling technique [46]. Figure 2.27 shows home-made plasma antenna for 5-20 KHz AC with the tube filled with argon and mercury at working pressure of 5 Torr. The tube with an inner diameter of 10 mm, an outer diameter of 12 mm and a length of 1200 mm was applied in this experiment. The shape of the tube was characterized as square-loop, with two 29

52 electrodes inserted in an insulating box. A coupling sleeve with a width of 30 mm was placed at the bottom around the tube and was shielded by a well-sealed shielding box (100 mm 60 mm 60 mm) made of cast aluminum. The coupling sleeve model was applied to the signal coupling system. The coupler was connected to transmission line to apply the useful signal. The distance between the center of the coupler and the electrode was longer than 200 mm. (a) (b) Figure 2.28: Plasma antenna. (a) Using a standard U-shape fluorescent lamp. (b) Coupling sleeve [47]. A plasma antenna using U-shape fluorescent lamp is presented in [47] as a receiver for the standard MHz FM radio band. The small RF coupling box envelopes the lamp as illustrate in Figure 2.28(a). Inside the box is coupling sleeve which is located at the end of fluorescent lamp as shown in Figure 2.28 (b). As depicted in Figure 2.28 (a) a BNC connector at the coupling sleeve and coaxial cable connect to a box containing the FM radio. The RF coupling to the plasma column is through a metal sleeve surrounding a short length of the tube. This coupling sleeve provides capacitive coupling for the FM signal from the plasma column inside the fluorescent tube to the coaxial cable then to the FM receiver 30

53 Figure 2.29 : Coupling structures. (a) Inductive coupling. (b) Double inductive coupling. (c) Capacitive coupling [48]. Besides, paper [48] presents a study of several power coupling structures for a plasma antenna and identified the most effective plasma generation in coupling technique. Also presented is a study that was undertaken with the aim of identifying the most efficient way of coupling an information signal for transmission using an already existing plasma column. The comparison was conducted for three coupling structures which are inductive, double inductive and capacitive. The coupling structures are shown in Figure Figure 2.30: Block diagram of the plasma antenna circuit and measurements systems [48]. A similar size of a copper tube was used to substitute plasma column for the coupling comparison in this paper [48]. The capacitive coupling has significant capacitance in the circuit. This is because the existence of dielectric tube between the coupling sleeve and the plasma, whereas with the inductive coupling option, it is possible that the antenna may not feed effectively off the ground plane. Hence prior to this comparison, a matching network must be included to ensure that the maximum 31

54 available power is transferred to the plasma column. Therefore a block diagram of plasma antenna circuit and measurement system as illustrated in Figure 2.30 was proposed in [48]. A double stub tuner was used to match the network and a signal selection is done by a low pass filter. Figure 2.31: Transmission characteristics (S 21 ) for two type of coupling structures with different configurations [49]. The comparison results in terms of transmission characteristic (S 21 ) are shown in Figure The findings explained that the double inductive was the least effective in coupling RF power into the plasma antenna. Longer inductive and capacitive couplers were found to be more effective than the short ones and these two structures were equally effective. Besides, the separation gap between the coupling sleeve and the ground plane had a little effect on the transmission characteristic. Meanwhile, Figure 2.32 shows examples of capacitive coupling used in paper [49]. Two coupling sleeves are shown in Figure 2.32, one is used to generate plasma and the other is used to send information signal in the form of surface wave. A copper ring was placed around the tube and was soldered to an N-type connector to pump the excitation of RF energy. A strong electric field was created between the ring and the ground plane, so that the electric lines penetrated inside the tube, exciting the plasma column. Another copper ring was mounted to apply the useful signal, using the same capacitive coupling. These two coupling sleeves were connected to two different ports. 32

55 Figure 2.32: Coupling sleeve in an excitation box [50]. Figure 2.33: Coupling between the two ports with (black) and without (gray) the conducting medium [50]. Figure2.34: Reflection coefficient of the signal port with (black) and without (gray) the plasma [50]. Figure 2.33 shows the measured coupling magnitude between the two ports when the plasma is excited. A copper tube is used to simulate the presence of conductivity. A strong coupling can be seen between exciting port and signal port. Figure 2.34 describes the measured reflection coefficient, S 11 with a similar condition in Figure

56 (a) (b) (c) Figure 2.35 : Three different kinds of couplers. (a) Solenoid Coupling. (b) Cubic coupling. (c) Cylindrical coupling [50]. In paper [50], the authors, analyzed three different kinds of couplers using CST Studio Suite. The comparison was conducted for three coupling structures which were solenoid coupling, cubic coupling and cylindrical coupling as shown in Figure In this design, a similar size of the fluorescent tube with a radius of m was used. From the analysis, the results for three different couplers showed that, solenoid coupling was easier to implement but it was not protected from EMI, has bad reflection coefficient magnitude and the radiation pattern of sample frequency was broadside with the directivity of 3.44 db and S LL db. Moreover, cubic coupling had better results than solenoid coupling, as it is protected from the EMI, has a good radiation pattern in sample frequency with the directivity of 2.59 db and SLL db but the implementation of a cubic aluminum around the tube is not so easy and also as said before it has low frequencies to resonance. Cylindrical coupling is similar to cubic coupling but it has more frequencies to resonance, easier implementation and it is more stable if implement it with two bonnets. So the cylindrical coupling is a 34

57 good way of coupling as the plasma antenna is shielded from EMI, with more frequencies for resonance and easy implementation but it depends on the application of the antenna to choose which coupling is better Shape of Plasma Antenna Investigation for plasma antenna radiation pattern for helix shape has been presented in [51]. Hence, an ideal helix plasma antenna design at target operating frequency in the UHF band was discovered. Figure 2.36: The ideal model of plasma helix antenna [51]. Figure 2.36 shows the geometry of the helix plasma antenna. It is assumed ideally that the plasma is excited at the joint between the plasma tube and the coaxial line, and the plasma density is uniform among the tube. The length of the coaxial line above the ground plane is denoted by h. The total height, L, number of turns, N, and diameter, D of the helix were chose to be cm, 4 and 9.54 cm respectively. The whole antenna was made of a thin tube wire of uniform radius a =0.5 cm. The diameter of the ground plane was r =12.5 cm, which was approximated to an infinite conductive plane. Based on Figure 2.37, the radiation patterns of plasma helix antenna is closer to the radiation pattern of metallic helix antenna when the plasma frequency is larger than the operating frequency. Figure 2.38 shows the return loss,s 11 of plasma helix antenna. 35

58 (a) (b) Figure 2.37: Comparison results for radiation pattern between metal antenna and plasma helix antenna. (a) Horizontal plane. (b) Vertical plane [51]. Figure 2.38: Return loss,s 11 of plasma helix antenna [51]. Figure 2.39: A model of a plasma whip antenna located on dielectric substrate with relative permittivity of 2.35 and the thickness, h is 2 mm [52]. Figure 2.39 shows the model of a plasma whip antenna located on the dielectric substrate with a relative permittivity = 2.35 and a height h =2 mm. The plasma whip antenna is composed of a glass tube with a relative permittivity of = 36

59 3.4 and a wall thickness of t = 2 mm. At moderate filling pressure the applied power will drive noble gas in the glass tube to ionize and form plasma. In this simulation a plasma rectangular cylinder model is chosen to reduce the staircasing error and the dimension of the plasma rectangular cylinder is d d l (d = 10mm). The plasma whip antenna presented in [52] was excited by a coaxial probe with a radius equivalent to 0.5 mm and the b was about twice of a. Besides, the inner conductor of the coaxial cable was immediately adjacent to plasma going through the both dielectric substrate and wall of the glass tube, while the outer conductor was connected to the ground plane. Figure 2.40, shows the comparison return loss result between of the plasma whip antenna and metal antenna. It was found that the plasma rectangular cylinder actually radiated electromagnetic wave as a conducting element. Figure 2.40: Comparison results of return loss between plasma whip antenna and metal antenna [52]. A plasma triangular monopole antenna that operate in the VHF band ( MHz) was studied in [53]. The plasma triangular monopole antenna as shown in Figure 2.41 was simulated using High Frequency Structural Simulator (HFSS). The simulation results indicated that, when the plasma frequency was sufficiently higher than the operating frequency and the collision frequency was corresponding low, the plasma antenna could operate with characteristics similar to a metal antenna. Besides, the peak gain of plasma antenna was lower than the metal, in operating bend angle range. 37

60 Figure 2.41 : A plasma triangular monopole antenna [53] Reconfigurable Plasma Antenna Reconfigurability, when used in the context of antennas, is the capacity to change an individual radiator s fundamental operating characteristics through electrical, mechanical, or other means [54], [55]. Reconfigurable antennas have attractive features such as the ability to reconfigure themselves autonomously to adapt to the changes or with the system to perform entirely different functions. Recently there has been interest in the use of plasmas as the conductor for antennas, as opposed to the use of metals. Plasma can be rapidly created and destroyed by applying electrical pulse to the discharge tube. Hence plasma antenna can be rapidly switched on and off. When it is off, it is non-conducting and invisible to electromagnetic radiations. When it is on, plasma becomes a good conductor. The plasma is highly conducting and acts as a reflector for radiation for frequencies below the plasma frequency [56]. Besides, due to their unique properties plasma antenna can be applied as a radiation pattern reconfigurable antenna. A reconfigurable plasma antenna presented in [57] was made of a 30 cm long plasma column which acted as a plasma antenna. The gas filled was argon gas. The operating parameters such as working pressure and radius of glass tube will be changed to transformed single plasma antenna to array plasma antenna as shown in Figure 2.42 (a) and (b). 38

61 (a) (b) Figure 2.42 : Plasma antenna. (a) Single plasma antenna. (b) Array plasma antenna [57]. By changing the operating parameters, single plasma antenna can be transformed into multiple antenna elements which are arranged in even numbered series (4, 6, 8, 10 and 12). The length and the numbers of plasma column can be controlled by the operating parameters such as input power and working pressure. From this work, the directivity of antenna increased when the number of plasma element increase. Figure 2.43 illustrates the radiation pattern between single and array plasma antenna. The red line represents radiation pattern array plasma antenna while the black line represents radiation pattern single antenna. Figure 2.43 : Comparison between normalized elevation radiation patterns of single and array plasma antenna [57]. Another work that is relate to reconfigurable plasma antenna is presented in [3]. The experimental setup of plasma antenna is shown in Figure The discharge tube was made from borosilicate (Pyrex) glass with a length 30 cm, while the diameter was 3 cm. 39

62 Figure 2.44 : The schematic diagram of plasma antenna [3]. From this paper, the plasma antenna was transformed from the single plasma antenna into array, helical and spiral plasma antenna. Figure 2.45 shows the helical plasma antenna filled with argon gas. It was observed that when changing the working pressure from 0.03 to mbar ( to Torr), the single plasma antenna could be transformed to array plasma antenna and when the working pressure was increased, the plasma antenna changed to helical plasma antenna and then spiral plasma antenna. Figure 2.45 : The helical plasma antenna [3]. On top of that, with monopole plasma antenna the reconfigurable characteristics can be realized under certain condition [5]. The radiation parameters for the plasma antenna array can be reconfigured through changing variable parameters of the plasma elements. To produce monopole plasma antenna, equipment such as discharge tube, RF power source and coupling device will be used. The experimental is illustrated in Figure Meanwhile, as shown in Figure 2.47(a) from 40

63 experiment, the length of plasma column had been shorter when the driven power was 15 W compared to plasma column in Figure 2.47(b) which was driven when power was 39 W. When the power increased, the plasma density also increased, so it could produce a good plasma column [58]. Figure 2.46 : The diagram of experimental setup [5]. (a) Figure 2.47: (a) The plasma column when driven power is 15 W. (b) The plasma column when driven power is 39 W [5]. Numerical calculations results demonstrated that when the excitation power is small, plasma density is not high; the reconfigurable properties of radiation pattern are unobvious. This work showed that if the plasma density increased, the radiation pattern was changed apparently with the increase of plasma density and excitation power. (b) 41

64 Figure 2.48: Plasma reflector antenna installed in anechoic chamber [59]. In addition, plasma can reflect the signals whose frequency is lower than plasma frequency while it will be transparent when the operating frequency is higher than plasma frequency [45]. From these advantages, the plasma antennas are highly reconfigurable and can be turned on and off. From this theory in paper [59], the plasma antennas used 17 commercially available fluorescent light tubes, with a nominal projected tube to tube spacing of 1.5 inches was designed. The length of the fluorescent light was 33.5 inches. The prototype of this antenna is shown in Figure The radiation pattern shown in Figure 2.49 for plasma is quite similar with its metal counterpart. It can be seen that when the plasma is de-activated, the reflected signal is dropped by over 20 db. These two scenarios have confirmed that the plasma reflector antenna is able to give similar performances as metal reflector. Figure 2.49 : Radiation Patterns of Plasma Reflector Antenna and Metal Reflector Antenna [59]. 42

65 Figure 2.50: Geometry of reconfigurable plasma corner reflector antenna [60]. This research presents simulation and experimental results in order to verify the performance and the radiation patterns of a reconfigurable plasma corner reflector antenna. Three different beam shapes were offered alternately. The reconfigurable plasma corner reflector antenna elements were made of a series of fluorescent lamps that were coordinated in a V arrangement as illustrated in Figure The halflambda distance of s= 0.5 required eight elements, while the lambda distance of s = 1.0λ required 16 elements for both reflector sides. The realized model was fabricated on a 3 mm thick ground plane as shown in Figure Figure 2.51 : The 24 plasma elements for reconfigurable plasma corner reflector antenna with a monopole antenna in the center of the ground plane [60]. 43

66 (b) Figure 2.52: Normalized H-plane radiation patterns. (a) Simulation. (b) Measurement [60]. The evolution of a single shape radiation pattern can be changed into a dualbeam shape as shown in Figure Unlike the omni-directional beam shape, the single beam shape could be formed by switching ON all plasma elements with s equal to 0.5λ, while elements with the s equal to 1.0λ are switched OFF. If doing otherwise, double-beam shapes will show up. If all elements are switched ON, the single beam remains without allowing the double beams to emerge. This is an alternative to form single-beam shape. 2.6 SUMMARY In this chapter, the basic of plasma such as fundamental of plasma and ionization process has been explained in detail. From the previous study shows that ionization process is important to generate plasma and to act as a conductor element. In addition, this chapter summarize from previous study method of generating plasma and plasma antenna technology including method of coupling sleeve, shape of plasma antenna and reconfigurable plasma antenna. The plasma antennas described in this chapter represent a selection of examples found in a review of the literature. Generally in current electronic communications industry requires high performance and efficient systems to meet the demands of today are continuously evolving applications. Physical limitations of microwave devices and circuits have stalled further improvements of current technology. In the midst of this scenario, the usage of plasma as conductive element in microwave devices has drawn growing interest due to their peculiar and innovative properties with respect to the traditional metallic circuits. From previous studies, highly ionized plasma is essentially a good conductor and 44

67 therefore, plasma filaments can serve as transmission line elements for electromagnetic wave transmission and reception. Besides, plasma antennas use plasma elements instead of metal conductor. They are constructed by an insulating tube filled with low pressure gases. The plasma rapidly created and destroyed applying proper radio frequency (RF) power pulses to the discharge tube so that the antenna is switched on and off. When the antenna is on, it exhibits a high conductivity, providing a conducting medium for the applied RF signal. The main advantage in using plasma antennas instead of metallic elements is that they allow an electrical rather than mechanical control. The conceptual structure of the proposed plasma antenna is demonstrated and discussed in more detail in the next chapter. 45

68 CHAPTER THREE RESEARCH METHODOLOGY 3.1 INTRODUCTION The number of industrial applications of plasma technologies is extensive and involves many industries including material processing, environmental control and communication system. In antenna application, plasma permits antenna structures to be reconfigurable with respect to shape, frequency, band- width, directivity and gain on millisecond to microsecond time scales. As a result, plasma may be able to form viable antenna array elements that weigh less and require less space than metal structures. When plasma is highly ionized, it essentially becomes a good conductor, and therefore plasma medium can serve as transmission line elements for guiding waves, or antenna surfaces for radiation. In the midts of this scenario, the usage of plasma as a conductive element in microwave devices has drawn growing interest due to their peculiar and innovative properties with respect to the traditional metallic circuits. Besides, the term plasma antenna has been applied to a wide variety of antenna concepts that incorporate the use of an ionized medium. In vast majority of approaches, the plasma, or ionized volume, simply replaces a solid conductor. This research focused on the development of antenna using plasma medium as a conductor element instead of using a metal element. Prior to that, the methodology of the research, which was divided into three stages, is presented in this chapter. The flowchart of each stage is included in the first section. Next, the fundamental of plasma parameter in plasma physics in described in section 3.3. Before the plasma antenna was designed, the estimation of plasma parameters, such as plasma frequency and collision frequency, were determined, as explained in section 3.4. Meanwhile, the fabrication and the measurement setup are presented in section 3.6, and followed by a summary in section

69 3.2 RESEARCH METHODOLOGY The research had been divided into three main stages. In the stage 1, a cylindrical monopole plasma antenna using argon gas, neon gas, and Hg-Ar gas (mixture of argon gas and mercury vapor) was successfully designed and simulated. In this stage, the aim was to analyze the interaction between plasma parameter and antenna performance. A literature review on the interaction of plasma element with electromagnetic waves antenna was done in first stage. Moreover, analysis process on the effects of different gases and different pressures with regard to antenna performance based on the simulation results had been investigated. In stage 2, the monopole plasma antenna using fluorescent lamp for Wi-Fi application was successfully developed. The investigation on several properties of the antennas that included the effect of coupling sleeve in plasma antenna was also reviewed in this stage. Comparison and analysis of different parameters of antenna, such as the length of plasma antenna and the diameter of plasma antenna, are presented in this stage. In stage 3, a development process of reconfigurable plasma antenna array was successfully developed. The aim target in this stage was to develop a reconfigurable antenna for beam steering, which was capable in steering 360 degrees of beam scanning by using plasma element instead of metallic element. The reconfigurable plasma antenna array used the fluorescent lamp as the plasma element. In order to reconfigure the radiation patterns of the antenna, the performances of the antennas on plasma activated (switched ON) and de-activated (switched OFF) states were investigated in this stage, and the analysis of the antenna performances is presented in this stage. The design was continues with 2.4 GHz for Wi-Fi application with optimization on monopole antenna as a radiation signal. After meeting the objectives as mention in chapter 1, the real product was fabricated, and next, was implement with switching system by using Arduino technology. In this research, Computer Simulation Software (CST) Microwave Studio was employed to design and simulate the proposed antenna in each stage. Meanwhile, the switching circuit was designed and simulated by using Arduino Technology. The simulated results were optimized until the best results were obtained with the consideration of the effects on antenna gain, reflection coefficient, Voltage Standing 47

70 Wave Ratio (VSWR), main lobe direction and operating frequency. The simulated antenna designs from stage 1 to stage 3 had been successfully fabricated and measured using laboratory test equipment such as vector network analyzer to validate the proposed topology and its synthesis. The flow of the research methodology for stage 1 to 3 illustrated in Figure 3.1(a), (b) and (c) respectively. 48

71 Start Problem Statement and Objectives Literature review on the interaction of plasma medium with electromagnetic waves and plasma antenna technology Design, simulation and optimization of the cylindrical monopole plasma antenna using argon gas, neon gas and Hg-Ar gas Meet the spec? NO YES Fabrication, measurement and analysis of the antenna NO Meet the objectives? YES End (a) 49

72 Start Problem statement and objectives Literature review on fluorescent tube as a plasma antenna and coupling sleeve method Design, simulation and optimization of the monopole plasma antenna using fluorescent tube with coupling sleeve at 2.4 GHz Meet the spec? NO YES Fabrication, measurement and analysis of the antenna NO Meet the objectives? YES End (b) 50

73 Start Problem statement and objectives Literature review on reconfigurable plasma antenna array Design, simulation and optimization of reconfigurable plasma antenna array Meet the spec? NO YES Fabrication and integration with Arduino system measurement and analysis of the antenna Measurement and analysis of the antenna NO Meet the objectives? YES End (c) Figure 3.1: Flow chart of the research. (a) Stage 1- cylindrical monopole plasma antenna. (b) Stage 2 - monopole plasma antenna using fluorescent lamp. (c) Stage 3- reconfigurable plasma antenna array. 51 YES YES

74 3.3 FUNDAMENTALS PARAMETERS OF PLASMA PHYSICS FOR PLASMA ANTENNA Plasma is a dispersive material that offers particular electrical properties when electromagnetic waves are applied to it. As a frequency dependent material, it also has these properties; electrical conductivity and electrical permittivity. These electrically controlled properties allow for the exploration of plasma as one of the material options in designing antennas. Hence, by understanding the relationship between plasma medium and incoming electromagnetic waves, it may lead to a promising development of plasma antennas. Plasma medium can be a good conductor when it is highly ionized and from this concept, the plasma medium can replace the metallic medium. Plasma filaments can serve as transmission line elements for guiding waves, or antenna surfaces for radiation. Therefore, it is necessary to understand the interaction between plasma medium and electromagnetic waves. The following section explains plasma properties and its relation with electromagnetic waves. The plasma medium is complicated in that the charged particles are both affected by external electric and magnetic fields, as well as contribute to them. Nonetheless, the resulting self-consistent system is nonlinear and very difficult to analyze. Furthermore, the inter-particle collisions, although also electromagnetic in character, occur on space and time scales that are usually shorter than those of the applied fields or the fields due to the average motion of the particles. Therefore, to make progress with such a complicated system, various simplifying approximations are needed. The explanation is started with consideration of a single particle motion model under the effect of electromagnetic field. The plasma derived in the following section is with an assumption of homogenous plasma Plasma Frequency One must distinguish between plasma frequency and the operating frequency of the plasma antenna. The plasma frequency is a measure of the amount of ionization in the plasma and the operating frequency of the plasma antenna is the same as the operating frequency of a metal antenna. The plasma frequency of a metal antenna is 52

75 fixed in the X-ray region of the electromagnetic spectrum whereas the plasma frequency of the plasma antenna can be varied. Being a medium of free charge carriers, plasma exhibits natural oscillations that occur due to thermal and electrical disturbances. The derivation starts with assumption on the harmonic oscillations of electrons around the ions. Due to harmonic oscillation the electron density can oscillate at an angular frequency ω p, and so the resulting electric field intensity E will oscillate at the same frequency [61]. The density oscillations give rise to a net free charge density ρ which is related to volume current density J as [62]: 3. 1 Which is called the Continuity Equation. Taking J =σe, 3. 2 The net free charge density ρ is related to the electric field intensity as 3. 3 Thus, equation 3.1, 3.2 and 3.3 are combined, 3. 4 The free charge density ρ becomes 3. 5 The contribution of ions to the plasma frequency was assumed neglect. When ion oscillation takes place within a shorter span than electrons, the electrons get heavier. Thus, the volume charge density expression in equation 2.5 can be assumed to depend only on oscillation of electron. Thus, the solution to the differential equation above is 3. 6 The angular frequency of oscillation of the free charge density ρ is also, thus, the plasma frequency is 53

76 3. 7 Besides that, from the volume of current density in the plasma the plasma frequency also can be derived due to electromagnetic wave interactions, Thus the plasma frequency numerical values of the parameters, the plasma frequency is is depicted in equation 3.7. By substituting the = Where: = Electron density = x C is the electron charge, = x kg is the electron mass. = x Free space permittivity Plasma Collision Frequency In studying plasma behavior, one of the plasma parameters that need to be identified is plasma collision frequency. Knowledge of the dependence of the effective electron-neutral collision in noble gas, such as argon, is very important in order to understand many of the plasma processes, especially for its fundamental and applications. This type of collision frequency is often referred to evaluate the energy transfer between particles. The collision frequency that occurs in gases is important in radio frequency field. 54

77 Consider a gas consisting of elastic hard spheres of type 1 into which a test particle of type 2 with velocity v is introduced. Both species of particles share similar radius a. The test particle will collide with particle of type 1 and cylinder container with a cross-sectional area σ. In a time interval t, a test particle with a velocity v covers a distance vt along this cylindrical volume of length, vt and cross section σ as it collides with other particles. If there are particles of type 1 per unit volume, the number of collision on the cylinder by the test particle is equal to the product of this number density and the volume of the cylinder The velocity v in equation (3.11) is usually given by a Maxwellian distribution, and the cross section σ is often velocity dependent. These velocity dependences are accounted for by defining an energy-dependent reaction rate coefficient [21] : Where is the Maxwellian distribution as shown in equation Equation 3.12 implies averaging σ over a Maxwellian distribution. Thus the number of collision per unit time or collision frequency, is, 1/s Where : = Collision frequency = Electron density σ = Collision cross section = electron speed 55

78 3.3.3 Conductivity of the Plasma Medium Conductivity of plasma medium is the most important parameter in plasma antenna. The charged particles that constitute the plasma will be under the effect of the Lorentz force when interacting with an electromagnetic wave. Firstly, consider this charged to be an electron, q where this particle must follow the Lorentz force which is known as momentum conservation equation [62]: Where q is the charge of the particle, v is the velocity of the particle, E and B are the electromagnetic and magnetic fields influencing the particle. For this initial analysis, it will be assumed that there is no static external electric and magnetic fields. If we take a transverse electromagnetic wave as in free space, the E and B fields are Where is the free space permeability constant and is the intrinsic wave impedance of free space. Consider only in time dependence of the fields, in the electric and magnetic field expressions is omitted as if it is included in the term. The term can be rewritten as Where c is the speed of light in free space. Thus B can be expressed as Hence, the resultant acceleration of the particle is Writing the acceleration and velocity in differential form and substituting equation 3.12 and 3.13 in equation 3.16, the equation become: 56

79 3. 21 Meanwhile, the acceleration components can be written as: From the above equations the velocity components for a charges particle can be obtained. Assume << c, the velocity component of the particles along the direction of propagation is smaller than the velocity of light, thus: The velocity and displacement in the x-direction can be written as From the formulation above, the integration constants are neglected, which are related to mean position and velocity of the charged particle during one period. By substituting equation 3.26 in 3.24,

80 From the above equation, acceleration, velocity and position components of the particles are all periodic. This implies that the mean position, energy and velocity of particles are all constant for each period. By calculating the velocity components; it is now possible to express the volume of the current density induced within the plasma by the electromagnetic wave. The current density can be written as Where is the electron volume density of the plasma and is the electron charge. In the above equation, it is assumed that the current flow is only in the x- direction, since the velocity of particles in the z-direction is negligible. Besides, the contribution of ion flow in the current density is neglected when the ion mass is greater than the electron mass. The particle mass term in the denominator of velocity expressions makes the velocity of ions smaller than electron velocity, making the contribution of ions negligible. In terms of electric field strength, the volume current density can be expressed directly as a: From equations 3.31 and 3.32, as well as substituting the velocity expression from equation 3.26, Where is the electron mass and is the electron volume density of the plasma. From the equation above, the conductivity of plasma medium can be expressed as Equation 3.34 is the conductivity equation for plasma medium in terms of particle charge, mass and density. Let s consider the effect of collision process with an assumption that the electrons lose all its energy during collision. Since only a collision less single-particle model was assumed in the beginning of the derivation, with the effect of collision (the in previous equations is now to represent more than one particle involved in the collisional case), Equation 3.15 now becomes 58

81 3. 35 With an introduction of as a collision frequency and if time dependence is assumed, then the left-hand side of equation 3.35 turns out to be From this result, the can replace by in equation 3.34 in order to include and consider the effect of collision frequency. Therefore, the conductivity is and if one assumes that there is only DC electric field and unmagnified plasma (isotropic cases),the conductivity of plasma medium is : From the expression it is observed that conductivity depends on the collision frequency of the plasma. As the collision frequency increases, the conductivity decreases due to the σ inversely proportional to the in the expression. This dependence of conductivity on the electromagnetic wave frequency is of great importance for the plasma antenna concept; while physical parameters of the plasma are determined based on the working frequency of the plasma antenna Complex Dielectric Permittivity of the Plasma Medium From equation 3.38, the complex permittivity of the plasma medium can be derived. The propagation constant of the electromagnetic wave in a conducting media can be obtained from the wave equations: The solutions to the wave equations are:

82 3. 42 Where η is the intrinsic wave impedance of the medium and k is the propagation constant. Substituting equation 3.41 in equation 3.39 the expression becomes is Since the t term in parentheses is the complex permittivity which And the propagation constant is From the above equation, the propagation constant depends on the relation between plasma frequency and wave frequency. 3.4 ESTIMATION OF PLASMA AND COLLISION FREQUENCY Before proceeding with designing the plasma antenna, two most important parameters, which are plasma frequency and collision frequency, need to be determined. These two parameters have a very significant influence in plasma antenna behavior if wished to be design. A computer coding program characterizing the characteristic of plasma medium is presented in [63]. Certain parameters, such as the type of gas, radius of discharge tube, discharge current, gas fill temperature, and gas pressure, have to be determined to run this program. Prior to this, an experiment has to be conducted in order to obtain all the required parameters values. This program will first calculate the electron density of the gas inside the discharge tube and from the electron density, the values of plasma frequency and collision frequency can be determined from equations 3.10 and Figure 3.2 below shows the flow chart of GLOMAC program (is a computer code for describing low pressure gas such as 60

83 electron density and electron temperature) that requires data obtained from the experiment to be inserted in. Set the gas ratio value for gas Insert measured tube radius value in cm Insert value for discharge current in Ampere (A) Insert value for gas pressure in Torr Insert gas fill temperature in Celsius Insert the cold spot temperature value in Celsius Insert the positive column (PC) in cm Insert cathode fall value (V) Insert wall axis temperature value in Celsius Figure 3.2 : Flow diagram of GLOMAC to calculate electron density for argon and neon gases. 61

84 Set the gas ratio value for gas Insert measured tube radius value in cm Insert value for discharge current in Ampere (A) Insert value for gas pressure in Torr Gas pressure = Argon gas pressure + mercury vapor pressure Set argon gas pressure 5 Torr Calculate mercury vapor pressure Insert gas fill temperature in Celsius Insert the cold spot temperature value in Celsius Insert the positive column (PC) in cm Insert cathode fall value (V) Insert wall axis temperature value in Celsius Figure 3.3: Flow diagram of GLOMAC to calculate electron density for mixture of argon and mercury vapor. First and foremost, the type of gas to be used was determined and the ratio of gas filling was set. In this research work, three different gases; argon, neon, and Hg- Ar (can be found inside fluorescent lamp) were used. As for argon and neon gases, the 62

85 gas ratios were assumed and set to be 1.0, while for the Hg-Ar gas, the ratio was assumed 0.9 for Argon and 0.1 for mercury [64]. Next, measure the radius of discharge tube in centimeter (cm). Then, get the value of discharge current by measuring the current flowing through the discharge tube. After that, set the value of gas pressure. Gas pressure values for argon gas and neon gas inside the discharge tube are known from an experimental work done by a researcher, Dr Ahmad Nazri Dagang at the Energy Conversion Laboratory, Faculty of Engineering, Ehime University, Japan. While for fluorescent lamp, there is no variation for the values of plasma parameters as they are fixed by design. Specification details on fluorescent lamp are limited and kept confidential by the manufacturer. Thus, experimental works need to be conducted in order to obtain the gas pressure value inside fluorescent lamp. Gas pressure of fluorescent tube is a combination of two types of pressure, which are vapor pressure of mercury (need to be calculated) and Argon gas pressure (standard range Torr, and 5 Torr was assumed in this experimental work) [65]. While for vapor pressure of mercury, a few steps were performed to obtain vapor pressure value. First, measure the outer wall temperature of the fluorescent tube with a portable digital thermometer TFN520 after the tube has been switched on and let it stabilize for about minutes. Then, add the measured temperature with the delta obtained from the formula presented in appendix D (Refer appendix D). The sum of delta T and measured temperature is herein taken as the temperature inside the lamp. After that, the obtained temperature inside lamp was compared with data for temperature versus vapor pressure from appendix E (Refer appendix E) In addition; interpolation was performed to retrieve the exact mercury vapor pressure value. The value of gas pressure inside the fluorescent lamp is the summation between mercury vapor pressure value and Argon gas pressure. Then, the gas fill temperature for the program was set to be equal to room temperature at 23 0 C. After the gas fill temperature was set, the cold spot temperature was obtained. This was done by measuring the temperature at three points, which were at both end and middle of the fluorescent tube. The highest temperature is known as Tc max, while the lowest value as Tc min. 63

86 Next, the length of PC and the cathode fall were determined for the fluorescent tube. The PC length represents the positive column of the fluorescent tube. It is a length measured from one end of an electrode inside the fluorescent tube to another electrode end (Refer appendix A). After that, a cathode value was required for this program. The formula to obtain the cathode fall value is presented below: V k = V- V p V p = E p L p Where: Vk : cathode fall voltage V : lamp voltage Vp : voltage of positive column Ep : electric field at positive column (for Hg fluorescent lamp is about 1V/cm) Lp : length of positive column 3.5 DRUDE DISPERSION MODEL FOR DESIGNING PLASMA The behavior of the plasma is given by drude dispersion model in CST software. The drude dispersion model describes the simple characteristic of an electrically conducting collective for free positive and negative charge carriers, where thermic movement of electrons is neglected. Figure 3.4 shows the graphical user interface for drude dispersion model in CST software. Figure 3.4: Defining a plasma in CST [66]. The plasma frequency ω p and the collision frequency ν c are called drude parameters. ɛ is the relative dielectric constant at infinite frequency, generally ɛ =1 The value of plasma frequency and collision frequency are obtained from equation 64

87 3.10 and 3.14 Plasma frequency is a natural frequency of the plasma and is a measure of the amount of ionization in plasma. One must distinguish the difference between the plasma frequency and the operating frequency of the plasma elements. The plasma frequency is a measure of the amount of ionization in the plasma, while the operating frequency of the plasma elements is similar to the operating frequency of a metal antenna. 3.6 FABRICATION AND MEASUREMENT SETUP In this section, the fabrication process for the designed plasma antennas and the set up for the measurement process are discussed briefly Fabrication process As mentioned in the previous chapter, the objective of this research was to focus on the interaction between RF and plasma medium. Thus, to look more into the mechanism of interaction between them, three fabrication processes were carried out. This section begins with the fundamental laboratory setup. It was necessary to produce plasma column as a conductor medium. The setup consisted of a vacuum and gas filling system, which was constructed with a vacuum pump, rotary pump, burner, pressure gauges, gas container, and piping lines. This setup was necessary to produce electrode-less discharge tubes for plasma discharge. Next was the construction of monopole plasma antenna using fluorescent tube, while the last part was fabrication for reconfigurable plasma antenna using low cost plasma, which was fluorescent tube Cylindrical Monopole Plasma Antenna Using Electrode-less Discharge Tube The discharge tube used in this work was a glass from glass borosilicate (Pyrex) with the length (L A ) of 160 mm inner and outer diameters of 9 mm (D I ) and 10 mm, (D O ) respectively as described in Figure 3.5(a). Besides, three types of gases were filled in this tube; argon gas, neon gas and Hg-Ar gas. For argon gas and neon gas the gas pressure is applicable at pressure 0.5 Torr, 5 Torr and 15 Torr respectively while for Hg-Ar gas the commercially fluorescent lamp is used as a cylindrical monopole plasma antenna. Figure 3.5 shows the real electrode-discharge tube. Due to lack of materials and setup in ARG, the electrode discharge tube was 65

88 specially ordered and fabricated at the Energy Conversion Laboratory, Faculty of Engineering, Ehime University, Japan. Moreover, as mentioned in the previous section, plasma can be produced by using Capacitively Discharge Plasma (CDP), Inductively Coupled Plasma (ICP) and Microwave Plasma (MP). CDP can be divided into two categories; Dielectric Barrier Discharge (DBD) and Capacitively Coupled Plasma (CCP). However in this research, DBD method is used to generate the plasma. Dielectric-barrier discharge (DBD) is the electrical discharge between two electrodes separated by an insulating dielectric barrier. Figure 3.5(b) shows the experiment setup for DBD method. The electronic ballast was used to energize the plasma column with the specification of output up to 1kV, Hz.The electronic ballast was connected to the DC power supply, while the coupling sleeve was connected to the feeding line with a 50 Ω SMA connector. On the other hand, a 20 GHz Vector Network Analyzer was connected to the SMA connector to couple the signal to the plasma column of the plasma antenna. The aluminum tape with a length of 100 mm and a width of 5 mm was fastened at the discharge tube. The aluminum tape functioned as external electrodes. When sufficient voltage was supplied between the two aluminum fasteners, the electron gas inside the discharge tube was accelerated by the electric field and produced ions, which is called ionization process, as mentioned in chapter two. Glowed tube indicated that the gas inside the tube was ionized to plasma and formed a plasma column. Figure 3.6 and Figure 3.7 show the glowed tube for neon and argon gases discharge tube at pressures 15 Torr. 66

89 (a) (b) Figure 3.5 : Monopole plasma antenna using electrode-less discharge tube. (a) Schematic diagram. (b) Construction of monopole plasma antenna. Figure 3.6 : Photograph of neon gas discharge tube at 15 Torr. 67

90 Figure 3.7: Photograph of argon gas discharge tube at 15 Torr Monopole Plasma Antenna Using Fluorescent Tube The plasma antenna was constructed using a commercially available fluorescent tube with mm length (L FT ) and 28 mm of diameter (D FT ) that works as radiating element in this study. The gas inside the fluorescent tube was a mixture of argon and mercury vapor. Figure 3.9 (b) represents the construction of the plasma monopole antenna. The tube was energized by electronic ballast with specification of V, Hz. Meanwhile, the AC power supply which was provided by a standard AC power supply was connected to electronic ballast before it was directed to both electrodes of the fluorescent tube. Electronic ballast was more preferred compared to magnetic ballast because electronic ballast is lighter in weight than magnetic ballast and more it had been proven to be more efficient compared to magnetic ballast. The function of ballast is to stabilize the current through the tube. Glowed tube indicated that the gas inside the tube was ionized to plasma and formed a plasma column. In this state, the plasma column became highly conductive and could be used as an antenna. For the coupling sleeve as shown in Figure 3.8, the position at the lower end of the tube as an input terminal, this is used to connect the plasma tube with external signals and measuring equipment. Copper wire with 5 numbers of turns is used and the end of copper wire is connected to SMA connector. The aluminum tape with length of 30 mm and width of 18 mm is wrapped at copper wire. The schematic diagram for monopole plasma antenna is illustrated in Figure 3.9 (a). 68

91 Figure 3.8 : Position of coupling sleeve. (a) (b) Figure 3.9: Monopole plasma antenna using fluorescent tube. (a) Schematic diagram. (b) Construction monopole plasma antenna. Figure 3.10 illustrates a monopole plasma antenna integrated with 3G Wi-Fi router. In this research work, a monopole plasma antenna using fluorescent tube was designed at frequency 2.4 GHz, which was suitable for Wi-Fi application. For 69

92 monopole plasma antenna to function as a Wi-Fi system, the antenna must be integrated with Wi-Fi wireless and router. This monopole plasma antenna was equipped with access-point 3G Wi-Fi router, which was installed inside the casing of the fluorescent tube. The Wi-Fi router was connected to the RF signal. Meanwhile, the function of the dongle was to supply 3G input signal. The RF signal supplied from the router passed through a 50 Ω cable and combined with the plasma element inside the fluorescent tube through coupling sleeve. The RF signal and the 3G input, which were injected to the plasma element, made this antenna to function as Wi-Fi technology. In addition, the Access Point Router (AP Router) was modified by removing the available printed antenna and replacing it with the constructed monopole plasma antenna. Hence, in order to ensure that the monopole plasma antenna could transmit and receive the signal, several measurement tests were performed. Figure 3.10 : Monopole plasma antenna integrated with 3G Wi-Fi router. Figure 3.11 : Monopole plasma antenna integrated with 3G Wi-Fi router during switch ON Reconfigurable Plasma Antenna Array Cylindrical-shaped fluorescent tube type T5 was used as reflective elements and coordinated in circular arrangement. The total number of fluorescent tubes used in the simulation was 12. The height of each element from ground plane surface was

93 mm, the diameter of the lamp is 16 mm, and the central monopole height was 35 mm with a diameter of 3 mm. On top of that, the angle between the centers of two adjacent elements was 30. (a) (b) Figure 3.12 : Geometry of reconfigurable plasma antenna array (a) Side view (b) Top view. The realized model was fabricated on 3 mm thick ground plane based on the geometry depicted in Figure The fabricated prototype is shown in Figure 3.13 (c). The top and the bottom parts of the reconfigurable plasma antenna array prototype are made from a type of polymer known as Nylon. Nylon was chosen in this design because of its natural behavior that cannot radiate the RF signal. In addition, excitation power to energize the 8 Watts fluorescent tubes was supplied by a set of electronic ballasts with specification of V, Hz. The AC power supply was connected to the electronic ballast before it was directed to both electrodes of the fluorescent tube. Each of the electronic ballast was controlled by a small single-pole switch. Each setup of electronic ballast required a set of four wires to be connected to each fluorescent tube. In overall, the design of this antenna had 12 electric ballasts and 12 switches as shown in Figure 3.13 (a) and (b). 71

94 (c) Figure 3.13: Prototype of reconfigurable plasma antenna array. (a) 3D AutoCAD drawing. (b) Connection of 1 of fluorescent tube. (c) Prototype of reconfigurable plasma antenna array. Moreover, the electric ballast was chosen instead of magnetic ballast as the element to energize fluorescent tube due its simplicity, less noise, and compact in size. The fluorescent tube was fixed at the bottom of the ground plane and was carefully glued to the ground plane. The gluing process was done one by one for the rest of the fluorescent tubes. The fluorescent tubes had to be in vertical alignment with respect to 72

95 the ground plane surface. Besides, the fluorescent tube was connected from the top electrode to the bottom electrode by using wires, which were hidden inside in the support holder. The support holder was made of Polyvinyl chloride (PVC). Meanwhile, the monopole antenna, which was located at the center of the fluorescent tube with a diameter of 3 mm, as shown in Figure 3.13 (a), was connected to the feeding line with a 50 Ohm SMA female connector Measurement setup To ensure that the antenna met the specifications and to test if the antennas functioned, antenna measurements were needed. In this section, the steps of measuring the antenna are presented Return Loss Measurement The measurements for S 11 and radiation pattern for all prototypes in this research had been conducted in the Antenna Research Centre, Faculty of Electrical Engineering. In addition, the calibration process was also done prior to each measurement to ensure the accuracy of the results. The vector network analyzer (VNA) consisted of two outputs. As depicted in Figure 3.14, the antenna under test (AUT) was directly connected to the VNA using output 2. This had been because; at that moment, output 1 experienced malfunction issue. The measurement results from the VNA were compared with the simulation results and the graphs were plotted by using SigmaPlot 10.0 software. Figure 3.14 : Setup for return loss measurement. 73

96 Radiation Pattern Measurement The measurement of antenna radiation patterns was done in an indoor anechoic chamber located at the Chamber Room of Antenna Research Centre, Faculty of Electrical Engineering, Universiti Teknologi MARA using the near-field measurement system. Figure 3.17 illustrates the arrangement of radiation patterns measurement in the indoor anechoic chamber. The chamber consisted of an azimuth turn table and a transmitter (TX) antenna on the polarization positioner. During measurement, the antenna under test (AUT) was placed on the azimuth turn table so that the AUT would be rotated based on the desired cut-plane. The distance between AUT and TX antenna was approximately 1 m. Moreover, the indoor anechoic chamber was linked with the measurement room where the equipment for radiation patterns measurement was located. The measurement equipment included a positioned controller signal generator, a spectrum analyzer, and control PC with antenna measurement software. The actual view of the indoor anechoic chamber and the measurement equipment are shown in Figures 3.15 and 3.16, respectively. Figure 3.15 : The radiation patterns measurement setup and the actual inside view of the anechoic chamber room. 74

97 Figure 3.16: The radiation patterns measurement setup and equipment for radiation patterns measurement. Figure 3.17 : The layout of the measurement setup for radiation pattern measurement Radiation Signal Measurement In this experiment the main objective is to prove that the received signal is transmitted from plasma antenna and not from coupling sleeve. The coupling sleeve was covered with aluminum shielding box with dimensions 52 mm 55 mm as illustrates in Figure 3.18 and Figure The main function of aluminum-wrapped shielding box was to enclose the radiation generated by coupling sleeve from radiated out from the box. In this experiment, the Wi-Fi router was ON and has been set to the 75

98 minimum transmission power. The signal strength of the monopole plasma antenna has been measured in three conditions; first is in condition where coupling sleeve was uncovered with aluminum-wrapped shielding box and fluorescent tube was switched ON, second coupling sleeve was covered with aluminum-wrapped shielding box and fluorescent tube was switched ON, third is coupling sleeve was covered with aluminum-wrapped shielding box and fluorescent tube was switched OFF. Results of these three conditions will be discussed and explained in chapter 5. Figure 3.18: Coupling sleeve is wrapping with aluminum shielding box. (a) Left view. (b) Right view. (c) Bottom view. (d) Top view. Figure 3.19 : Coupling sleeve is wrapping with aluminum shielding box. (a) Front view during fluorescent tube switched OFF. (b) Front view during fluorescent tube switched ON. 76

99 Measurement of Radiation Signal from Monopole Plasma Antenna as a Transmitter d=1m Figure 3.20 : Experimental setup for plasma antenna that serves as a transmitter. The plasma antenna was connected to an RF signal generator through the coupling sleeve. The RF signal generator was set to generate a continuous wave at 2.4 GHz. Besides, when excited by this alternating current, the antenna radiated radio waves and acted as a transmitter. Apart from that, a reference metal monopole antenna was used as the receiving antenna, and the signal captured by receiver was observed using a spectrum analyzer. The spectrum analyzer was used to measure the captured frequency and the power density of each frequency component. The distance, d, between transmitter and receiver was 1 m. Then, the experiment was preceded with RF generator in the turn off mode, and the results were compared and discussed in Section of chapter five. Figure 3.20 represents the experimental setup for plasma antenna that served as a transmitter Measurement of Radiation Signal from Monopole Plasma Antenna as a Receiver Figure 3.21: Experimental setup for plasma antenna that serves as a receiver. 77

100 In this experiment, the plasma antenna was connected to the spectrum analyzer through the coupling sleeve, and served as a receiver instead. The reference metal monopole antenna was connected to the RF signal generator and served as a transmitter. The RF signal generator was set to generate signal in a similar frequency range as conducted in the previous experiment. The distance, d, was also fixed at 1 m. The signal transmitted from RF generator was captured by plasma antenna and was measured using the spectrum analyzer. Then, similar measurements were done when the plasma antenna was de-energized and was removed from the receiver system. Figure 3.21 represents the experimental setup for plasma antenna as a receiver Measurement of Signal Strength Monopole Plasma Antenna In antenna, the signal strength at a specific point can be determined from the power delivered to the transmitting antenna. This signal strength can be observed using a Wi-Fi analyzer, which is software that can be installed on the smart phone. Wi-Fi analyzer is one the applications on the Android system which was used to observe the signal strength of Wi-Fi channels on the wireless router. In this research work, the monopole plasma antenna served as a transmitter at a distance of 3 meter as shown in Figure Figure 3.22: Testing the signal strength of monopole plasma antenna. 3.7 SUMMARY In the beginning of this chapter, a brief review of research methodology has been discussed. Elaboration pertaining to the fundamental parameters of plasma was also given. In this work, in order to determine the plasma parameters, such as plasma 78

101 frequency and collision frequency, the software GLOMAC was used. Besides, experimental approach was adopted to retrieve some values of parameters. After obtaining the plasma parameters, the plasma antenna was designed using the Drude model in Computer Simulation Software (CST) Microwave Studio. The methods used to develop and to measure plasma antenna performances are also presented in this chapter. The plasma antenna for cylindrical monopole plasma antenna using discharge tube and monopole plasma antenna with fluorescent tube utilized the plasma as the radiating element, while for reconfigurable plasma antenna array using fluorescent tube used plasma element as a reflecting elements. To construct the monopole plasma antenna using fluorescent tube and reconfigurable plasma antenna array using fluorescent tube, the available fluorescent lamps in the market were used. Based on this concept, the design of plasma antenna is further described in detail in the next chapter. The performance of the defined plasma model is measured and explained in the following chapter. The similarity between the measured and the simulated results is reconfirmed in the defined plasma model. 79

102 CHAPTER FOUR A CHARACTERICTICS OF CYLINDRICAL MONOPOLE PLASMA ANTENNA 4.1 INTRODUCTION In this present study, the analysis of cylindrical monopole plasma antenna for electrode-less discharge tube by using CST microwave studio was carried out, as it has not been established yet. Experiments performed before have verified that monopole plasma antenna possessed many properties similar to monopole metallic antenna. When the tubes of plasma antenna were energized, they were turned into conductors, and could transmit and receive radio signals. When de-energized, these revert to non-conducting elements and failed to reflect probing radio signals [37]. These make plasma antenna to have more unique properties compared to metallic elements, as they allow electrical rather than physical control. However, for plasma antenna to behave like a conducting element, some parameters, such as pressure of gases and type of gases, are necessary and need to be identified for antenna performances. This chapter discusses the analysis for the characteristics of cylindrical monopole plasma antenna and three different gases with three different pressures which were argon gas, neon gas and Hg-Ar gas (a mixture of mercury vapor argon gas) that employed plasma as its radiating element. In this experiment for argon gas and neon gas, cylindrical monopole plasma antennas were fabricated using glass borosilicate (Pyrex) with a dielectric permittivity = 4.82 and a length of 160 mm, diameter of 10 mm and thickness of 1 mm. Meanwhile, commercial fluorescent tube was used for Hg-Ar experiment. The glass material that use in commercial fluorescent tube was borosilicate (Pyrex) [67]. The discharge tubes were filled with argon gas and neon gas at pressures of 0.5 Torr, 5 Torr and 15 Torr. A brief description on electrodeless discharge tube is given in section 4.2. In this work, the Dielectric Barrier Discharge (DBD) method was used to produce the plasma. The experiment setup was described in chapter 3. Moreover, the design procedure using CST microwave studio 80

103 is presented in section 4.3 too. The effect of plasma frequency on propagation of electromagnetic wave is explained in section 4.4. Besides, an analysis on cylindrical monopole plasma antenna design, which included two cases of different pressures and different gases, is described in section 4.4. Based on analysis, the frequency at 4.6 GHz because of the limitation and unavailability of material and technology to produce discharge tubes. However, based on literature review, 4.6 GHz frequency will produce the same concepts analysis as 2.4 GHz frequency. The simulation and the measurement results of cylindrical monopole plasma antenna are presented in section 4.5, and followed by a summary in section ELECTRODE-LESS DISCHARGES FOR DIELECTRIC BARRIER DISCHARGE An electrode-less discharge is a discharge that has no internal electrodes in which the power required to generate plasma is transferred from outside the discharge tube to the gas inside via an electric or magnetic field. Capacitively Discharge Plasma (CDP) is one of type mechanism to generate plasma using electrode-less discharge. CDP can be divided into two categories which is Capacitively Coupled Plasma (CCP) and Dielectric Barrier Discharge (DBD). In this work, the DBD method was chosen because of it is easier and simpler to setup the experiment and cheaper to generate the plasma. A dielectric barrier discharge (DBD), is one of the most common types of industrial plasma sources. It was discovered by W. Siemens in 1857 for the purpose of "ozonizing" air DBDs have for a long time been regarded as the ozonizer discharge [68]. DBD devices can be made in many configurations, typically planar, using parallel plates separated by a dielectric or cylindrical, using coaxial plates with a dielectric tube between them. It essentially consists of two electrodes separated by a small distance of a dielectric material. Typical voltages applied to the electrodes vary from hundreds to thousands of volts. A basic circuit diagram of DBD is shown in Figure 4.1. When an electric field is generated between two external electrodes (such as aluminum tape), electrons in the gas respond to the field and acquires energy while the ions, being heavier and acquire less kinetic energy compared to electrons. The high-energy electrons can ionize the gas directly or indirectly by collisions thus 81

104 producing secondary electrons. When the electric field is strong enough, it can lead to what is known as an electron avalanche and the gas becomes electrically conductive due to abundant free electrons. The excitation and ionization processes are repeated and plasma is produces and sustained. Figure 4.1: A simple schematic diagram of a capacitive discharge [33]. 4.3 DESIGN OF CYLINDRICAL MONOPOLE PLASMA ANTENNA As mentioned in the previous section, the main objective of this chapter had been to analyze the characteristic of interaction between plasma medium and RF microwave. Three types of gases were utilized; argon, neon, and Hg-Ar (a mixture of mercury vapor and argon gas) gases with 0.5 Torr, 5 Torr, and 15 Torr respectively. The design of the cylindrical monopole plasma antenna with different gases and pressure is explained in detail. In addition, the characteristics of the varying pressures and gases are analyzed in this section Design Procedure To simulate the performance of a plasma monopole antenna design, CST MWS software was used. Before the antenna was designed, the plasma properties, such as plasma frequency and collision frequency, were inserted first in Drude dispersion model in CST software. The Drude dispersion model describes simple characteristics of an electrically conducting collective of free positive and negative charge carriers, where thermic movement of electrons is neglected. The values of plasma frequency and collision frequency can be obtained from equations 3.10 (plasma frequency) and 3.14 (collision frequency) in chapter 3 and the electron density can be determined by using GLOMAC software as explained in chapter 3. 82

105 4.3.2 Structure of Cylindrical Monopole Plasma Antenna Figure 4.2 shows the dimensions of the cylindrical discharge tube that was used in the experiments. The tube was 160 mm in length, while the inner and the outer diameters were 9 mm and 10 mm respectively. The glass material was borosilicate (Pyrex) with a dielectric constant 4.82 and aluminum tape was used to fasten both opposite sides of discharge tube as an energy transfer medium. Function of aluminum tape as an external electrode to generate plasma column. Besides, a coupling sleeve was positioned at the lower end of the tube and the Vector Network Analyzer was connected between the coupling sleeves and the discharge tube. Number of turns of coupling sleeve is four [69]. Figure 4.3 shows the real prototype of cylindrical monopole plasma antenna. In simulation there was no need to design the aluminum tape because in CST Microwave studio, plasma could be generated by using the drude model. Table 4.1 summaries the parameters of a cylindrical monopole plasma antenna. a Figure 4.2: The schematic diagram of discharge tube. Figure 4.3: Discharge tube used in this experiment. Table 4.1: The parameters of a cylindrical monopole plasma antenna Parameter Label Diameter(mm) Length of discharge tube L A 160 Outer diameter of discharge tube D O 10 Inner diameter if discharge tube D I 9 83

106 Distance coupling sleeve at the bottom of discharge tube L B ANAYLSIS OF CYLINDRICAL MONOPOLE PLASMA ANTENNA In this section, the analyses for three types of gases, which were Argon, Neon, and Hg-Ar gases are presented. Every gas consisted of pressures 0.5 Torr, 5 Torr, and 15 Torr respectively. The reason this research used these three gases had been because they were inexpensive materials. Besides, the effects of the plasma parameters were analyzed to identify if plasma medium could function as a conductor element Effect of Plasma Frequency on Complex Permitivity In general, plasma frequency determines if the plasma medium can act as a metal or an absorber. One of the electrical properties of a medium that is important in applications of electromagnetic is electrical permittivity. With this parameter known, propagation of electromagnetic waves in plasma medium can be inspected thoroughly. Theoretically, the plasma possesses some conduction properties. When the plasma frequency is higher than the electromagnetic wave frequency (ω p >ω), the electromagnetic wave will be reflected as the plasma behaves as a conductor and it can be used to radiate radio signal. Nonetheless, when the plasma frequency is lower than the electromagnetic wave frequency (ω p <ω), the electromagnetic wave radiation passes through the plasma and the plasma becomes transparent. The electrical conductivity of plasma determines how good the plasma is if it is meant to radiate radio signals. In other words, the electrical conductivity of plasma plays a major role whenever plasma is used as a radiator. In plasma, the imaginary part in complex permittivity represents losses in the medium and the real part indicates the energy stored in the medium ( -j ) [71-72]. Based on equation 3.45, permittivity depends on plasma frequency, electron density, and microwave frequency. In this section, the analysis of complex permittivity for cylindrical monopole plasma antenna conductivity for Argon, Neon, and Hg-Ar gases was looked into with pressures 0.5 Torr, 5 Torr, and 15 Torr. 84

107 (a) (b) 85

108 (c ) Figure 4.4: Relative Permittivity for argon gas, neon gas and Hg-Ar gas for (a) 0.5 Torr (b) 5 Torr and (c) 15 Torr. Figure 4.4 illustrates the plasma complex permittivity based on Drude model for argon gas, neon gas and Hg-Ar gas at pressures (a) 0.5 Torr, (b) 5 Torr and (c) 15 Torr respectively. From the graph, the value of imaginary increases when the operating frequency is decreased while the real part becoming more negatively when the operating frequency decreased thus loss in plasma will increase for three gases. Meanwhile, as for Hg-Ar gas at 0.5 Torr as a plasma antenna, the operating frequency must greater than 1 GHz (>1 GHz). This because from the Figure 4.4 (a) shows that when the operating frequency is less than 1 GHz (< 1 GHz) the loss in plasma is increase while for Argon gas and Neon gas the starting operating frequency that suitable to act as a plasma antenna at frequency 2 GHz (>2 GHz). On the other hand, Figure 4.4 (b) portrays that the loss for Hg-Ar gas is extremely slow at frequency range >1.8 GHz at 5 Torr. For Argon gas the loss began to decrease at an operating frequency of >3 GHz, while for Neon gas, the loss occur when the operating frequency below than 2 GHz at pressure of gas at 5 Torr. Apart from that, Figure 4.4(c) clearly shows that Hg-Ar gas the loss extremely slow at operating frequency > 2 GHz for pressure 15 Torr. However, for Neon gas and Argon gas the loss started to decrease at operating frequency >6 GHz for pressure 15 Torr. 86

109 4.4.2 Effects of Different Pressures Relationship between plasma parameter and radio frequency waves were explained in detail in this section. The effect of different pressures for same gas were investigated and analyzed. The analysis was cover for reflection coefficient, VSWR, gain, directivity and radiation pattern Argon Gas In the periodic table, argon is a one of the noble gases and it is in group 18. Incandescent lights are filled with argon to preserve the filaments at high temperature from oxidation. It is used for the specific way it ionizes and emits light, such as in plasma globes and calorimeter in experimental particle physics. Gas-discharge lamps filled with argon provide the color light blue. Figure 4.5: The effect on reflection coefficient, S 11 for different pressure for Argon gas. In this case, the effect of different pressure for Argon gas on reflection coefficient, S 11 has been investigated. As for cylindrical monopole plasma antenna at operating frequency 4.6 GHz, the reflection coefficient, S 11 for pressure 0.5 Torr is db, 5 Torr is db and 15 Torr is The design of the antenna is portrayed in Figure 4.2. As depicted in Figure 4.5, it clearly shows that the different pressure has significant effect on reflection coefficient, S 11. It can be seen that the pattern for return loss shifted to the downward at the operating frequency of 4.6 GHz when the pressure is increase. From numerical calculation of GLOMAC as explained 87

110 in chapter 3, the electron density,n e for 0.5 Torr, 5 Torr and 15 Torr; n e = m -3, n e = m -3 and n e = m -3 respectively. Figure 4.6: The effect on VSWR for different pressure for Argon gas. Meanwhile, Figure 4.6 shows the effect on VSWR for different pressure with the same gas. From the graph, the VSWR for three different pressures show below than 2 at operating frequency of 4.6 GHz. The value of VSWR indicates how well an antenna is matched to the cable impedance where the reflection, Γ = 0. This means that all power is transmitted to the antenna and there is no reflection. Although the optimal value of VSWR is 1, it must be lower than 2 so that the antenna yields a return loss of more than 10 db [71]. Figure 4.7: Comparison of different pressure for Argon gas radiation patterns in polar-plot. The radiation pattern in polar plot for Argon gas at pressures 0.5 Torr, 5 Torr and 15 Torr have been compared at operating frequency 4.6GHz. The radiation pattern 88

111 is referred at E-plane (phi=90 o ). As clearly shown in Figure 4.7, they are similar in shape. The results indicate that at main lobe direction, 0.5 Torr Argon have the highest gains as compared to the 5 Torr and 15 Torr. The gain for 0.5 Torr is equal to dbi while for 10 torr and 15 torr are dbi and dbi respectively. Hence, this analysis proved that, when the pressure is increase, the gain wills decrease. It is due, when the pressure increase, the collision will increase as well. The collision frequency,ν c for 0.5 Torr is /s, 5 Torr = /s and 15 Torr = /s. From equation 3.38 the collision frequency, ν c is inversely proportional to the plasma conductivity,σ. When collision frequency increase, the plasma conductivity,σ will decrease. The plasma conductivity,σ which was obtained from equation 3.38 showed that at pressure 0.5 Torr, σ = S/m, 5 Torr, σ = S/m and 15 Torr, σ = 5.48 S/m. Hence, it can influence the value of gain antenna. Table 4.2 shows the summary of simulation comparison results for antenna performances. Table 4.2: The performance of cylindrical monopole plasma antenna using argon gas Pressure(torr) Reflection VSWR Plasma Gain(dBi) Directivity(dBi) coefficient,s 11 (db) conductivity (S/m) Neon Gas Neon is the second-lightest noble gas, after helium. It is in group 18 (noble gases) in the periodic table. Neon is used in vacuum tubes, high-voltage indicators, lightning arrestors, wave meter tubes, television tubes, and helium neon lasers. Besides, neon has been used to build plasma antenna since it is inexpensive. 89

112 Figure 4.8: The effect of reflection coefficient,s 11 for Neon gas at different pressure. Figure 4.8 shows the comparison of simulated reflection coefficient, S 11 for Neon gas at pressures 0.5 Torr, 5 Torr and 15 Torr at an operating frequency of 4.6 GHz. From Figure 4.8, the reflection coefficient, S 11 at pressure 0.5 Torr is db, 5 Torr is db and at 15 Torr is db. It clearly shows that the pattern of return loss is slightly similar to Argon gas, whereby the pressure increase as the resonant frequency shift to the downward. By using GLOMAC software, the value of electron density,n e at pressure 0.5 Torr is m -3, 5 Torr is n e = m - 3 and 15 Torr is n e = m -3. Figure 4.9: The effect of VSWR for different pressure for Neon gas. As depicted in Figure 4.9, the VSWR for three different pressures for Neon gas have been compared. From the figure, the VSWR all the three different pressures are below than 2 at frequency 4.6GHz and show that the antenna is well matched to the cable impedance where the reflection is =0. 90

113 Figure 4.10: Comparison of different pressure for Neon gas radiation patterns in polar-plot. Figure 4.10 illustrates the simulated results of radiation pattern in polar plot at E-plane (phi=90 ) for three different pressures for Neon gas at a frequency of 4.6 GHz. The results show that the radiation patterns of monopole plasma antenna using neon gas as a plasma medium look similar with each other. The pattern gain for Neon gas is almost similar with the argon gas. It can also be noted from Figure 4.10, that antenna gain generated by 0.5 Torr is dbi higher than 5 Torr (4.717 dbi) and 15 Torr (4.550 dbi). Meanwhile, the collision frequency, ν c at pressure 0.5 Torr is ν c = /s, 5 Torr is ν c = /s and 15 Torr ν c = /s. By using equation 3.38, plasma behaves as a metal when plasma conductivity,σ for 0.5 Torr, 5 Torr and 15 Torr obtained are σ = S/m, σ = S/m and σ = 8.10 S/m respectively. Figure 4.10 describe from simulation result, when increase the pressure, the gain will decrease. This because from equation 3.38, the plasma conductivity,σ will decrease when collision frequency increase. Thus the gain of cylindrical monopole plasma antenna also decreases. Table 4.3 summarizes the simulation results for 0.5 Torr, 5 Torr and 15 Torr respectively for neon gas. 91

114 Table 4.3: The performance of cylindrical monopole plasma antenna using neon gas. Pressure(Torr) Reflection coefficient,s 11 (db) VSWR Plasma Conductivity (S/m) Gain(dBi) Directivity(dBi) Hg-Ar gas Most of the discharge lamps in use at the present time are the mercury-argon; Hg-Ar gas fluorescent lamps. Their high performance in converting electrical power to light, size flexibility, and good color rendering properties make them the most successful lamp product. Light is mainly produced by conversion of short wavelength UV radiation to visible radiation with the phosphor coating on the inner wall of the tube. A typical hot cathode fluorescent lamp consists of a glass tube with its inner surface coated with fluorescent powder. It is filled with argon gas, a drop of mercury, and the filaments are tungsten wire electrodes coated with a thermionic emitter sealed into each end of the tube [72]. The rare gas argon is added to the lamp primarily to assist starting since the vapor pressure of mercury is very low initially. Figure 4.11: The effect of reflection coefficient,s 11 for different pressure for Hg-Ar gas. Figure 4.11 illustrates the comparison of simulated results for reflection coefficient, S 11 when the pressure varied from 0.5 Torr until 15 Torr for Hg-Ar gas. 92

115 From the graph it clearly shows that when the pressure is increased, the resonant frequency 4.5 GHz shifted to the downward. The value of reflection coefficient, S 11 at pressure 0.5 Torr is S 11 = db, 5 Torr is S 11 = db and 15 Torr is S 11= db. The electron density, n e obtained for 0.5 Torr is n e = m -3, 5 Torr = is n e = m -3 and 15 Torr is n e = m -3. Figure 4.12: The effect of VSWR for different pressure for Hg-Ar gas Figure 4.12 clearly shows the simulation results for VSWR for different pressure for fluorescent tube. At frequency 4.5GHz, the VSWR of plasma antenna with pressure 0.5 Torr, 10 Torr and 15 Torr is 1.07, 1.06 and 1.03 respectively. Figure 4.13: Comparison of different pressure for Hg-Ar gas radiation patterns in polar-plot As depicted in Figure 4.13, the radiation pattern for cylindrical monopole plasma antenna using Hg-Ar gas at three different pressures look similar to ideal 93

116 monopole antenna. The radiation pattern also will change with the variation of pressure in monopole plasma antenna. From figure 4.14, the gain is increase when the pressure is decrease. The simulated peak gain yield at 0.5 Torr is dbi while for 10 Torr and 15 Torr are dbi and 15 Torr dbi respectively. Meanwhile, plasma conductivity,σ obtained from equation 3.38 shows that the value of σ = S/m at pressure 0.5 Torr, σ = 9.58 S/m at pressure 5 Torr and σ = 4.89 S/m at pressure 15 Torr, As mentioned before this, the plasma conductivity,σ is inversely proportional to the collision frequency. From of Hg-Ar pressure, 0.5 Torr ν c = /s, 5 Torr ν c = /s and 15 Torr ν c = /s. When increase the pressure the collision frequency also increase and as a results the plasma conductivity will decrease. Hence, the performance of antenna in terms of gain will decrease. Table 4.4: The performance of monopole plasma antenna using Hg-Ar gas. Pressure(Torr) Reflection coefficient,s 11 (db) VSWR Plasma Conductivity (S/m) Gain(dBi) Directivity(dBi) Comparison of Different Gases Performance In this section, the effects of different gases were analyzed and compared. The characteristics of the three different gases such as return loss, VSWR, plasma conductivity, gain, directivity and radiation pattern, are presented in this section. 94

117 (a) (b) (c) Figure 4.14: The effect of reflection coefficient,s 11 for different gas at (a) 0.5 Torr (b) 10 Torr and (c) 15 Torr. Figure 4.14 shows the simulated reflection coefficient,s 11 for Argon gas, Neon gas and Hg-Ar at (a) 0.5 Torr, (b) 5 Torr and (c) 15 Torr. From the Figure 4.14(a) when pressure is fix to 0.5 Torr the resonant frequency for fluorescent tube is slightly shifted to the right (4.5 GHz) compared to Argon gas and Neon gas which is the resonant frequency for both are at 4.6 GHz. Besides, the reflection coefficient, S 11 is measured at 4.6 GHz for Argon gas and Neon gas at pressure 0.5 Torr are db 95

118 and db respectively during simulation while for Hg-Ar at frequency 4.5 GHz is db. For pressure 5 Torr the reflection coefficient, S 11 for Argon gas and Neon Gas at frequency 4.6 GHz are db and db respectively. For Hg-Ar at resonant frequency 4.5 GHz the of reflection coefficient, S 11 is db. Moreover, when the operating frequency at 4.6 GHz for Argon gas and Neon gas at pressure 15 Torr the reflection coefficient, S 11 are db and db respectively while for Hg-Ar the reflection coefficient, S 11 is db at 4.5 GHz. The reflection coefficient,s 11 for Argon gas and Neon gas is look similar to each other. This might be because Argon and Neon gases are noble gases and are positioned in the same group in the periodic table. The same pattern of reflection coefficient, S 11 is clearly shown at Figure 4.14 (b) and Figure 4.14 (c) when the pressure at 5 Torr and 15 Torr. Besides, the results from the analysis of VSWR for different gases of cylindrical monopole plasma antenna are depicted in Figure The simulated VSWR for different gases is below than two and indicates that the cylindrical monopole plasma antenna is matched to the transmission line and the power is delivered to the antenna. (a) 96

119 (b) (c) Figure 4.15: Comparison of simulated VSWR for different gases at (a) 0.5 Torr (b) 5 Torr and (c) 15 Torr. The radiation patterns of antenna for different gases are illustrates in Figure From the Figure 4.16 it clearly shown that the pattern of radiation pattern for Argon and Neon gases look similar at pressure 0.5 Torr, 5 Torr and 15 Torr. Based on these results, at pressure 0.5 Torr, 5 Torr and 15 Torr, Neon gas achieved higher gain compared to Argon gas and Hg-Ar gas. As can be seen from the tables 4.5, 4.6 and 4.7, the antenna gain increases correspond to the increment of plasma conductivity values. The value of antenna gain compared to type of gases is in order of Ne > Ar > Hg-Ar at all for different pressures. Neon shows the highest value of antenna gain while Hg-Ar shows the lowest. Even though the values of collision frequency is in order of Hg-Ar > Ar > Ne, which means more collision should be occurred in Hg-Ar and Ar tubes compared to Ne tube. However, when look at the size and mass of atom/molecule, the order is Hg-Ar > Ar > Ne, where neon is the lowest in terms of size and mass. For Hg-Ar gas: 97

120 (atomic no: 80, atomic mass: u, atomic radius: 171 pm), for Argon gas: (atomic no: 18, atomic mass: 39.95u, atomic radius: 71pm) and for Neon gas: (atomic no: 10, atomic mass: 20.18u and atomic radius: 38pm) [73-74]. When the size is big it is easy for the atom to collide with the surrounding particles due to its high surface area to volume ratio. In contra, when the mass of atom is high, the collision that occurred will give less impact due to the decrease of the effect from the elastic collision. Hence, the values of antenna gain strongly affected by size and mass of atom which subsequently will give effect to the impact of collision itself. The decrease of elastic collision will reduce the electron mobility which consequently effect to the level of conductivity where the antenna gain is depend on [75]. Tables 4.5, 4.6 and 4.7 portray the summary of simulated results for different gases at pressure 0.5 Torr, 5 Torr and 15 Torr respectively. (a) (b) 98

121 (c) Figure 4.16: The effect of radiation pattern in polar plot for different gas at (a) 0.5 Torr (b) 5 Torr and (c) 15 Torr. Table 4.5: The performance of monopole plasma antenna for different gases at pressure 0.5 Torr. Type of Gases Reflection coefficient, S 11 (db) VSWR Electron Density (m -3 ) Collision Frequency (1/s) Plasma Conductivity (S/m) Gain (dbi) Directivity (dbi) Ar Ne Hg-Ar Table 4.6: The performance of monopole plasma antenna for different gases at pressure 5 Torr Type of Gases Reflection coefficient, S 11 (db) VSWR Electron Density (m -3 ) Collision Frequency (1/s) Plasma Conductivity (S/m) Gain (dbi) Directivity (dbi) Ar Ne Hg-Ar

122 Table 4.7: The performance of monopole plasma antenna for different gases at pressure 15 Torr Type of Gases Reflection coefficient, S 11 (db) VSWR Electron Density (m -3 ) Collision Frequency (1/s) Plasma Conductivity (S/m) Gain (dbi) Directivity (dbi) Ar x x Ne x x Hg-Ar x x RESULTS AND DISCUSSION To provide a better analysis, the measured return loss and radiation pattern for the three types of cylindrical monopole plasma antenna are presented. The Rhode and Schwarz Vector Network Analyzer ZVB20 were used to measure the reflection coefficient, S 11. To start the measurement, the equipments needs to be calibrated first, systematic error from the measurement can be removed. On top of that, the antenna reflection coefficient, S 11 was measured at the anechoic chamber. The comparison results between simulation and measurement for argon gas, neon gas and Hg-Ar (can be found inside commercial fluorescent lamp) are presented in this section. For two gases; argon and neon the comparison between simulation and measurement at 0.5 Torr was chosen because based on the analysis from the simulation result, 0.5 Torr was the optimum pressure value which offered higher gain. Pressure use in Hg-Ar gas is 0.6. Torr; which is the pressure refers to commercial product in market. Therefore comparison pressure between simulation and measurement is 0.5 Torr (for argon and neon gases) while for Hg-Ar gas is 0.6 Torr therein presented in this section. 100

123 (a) (b) (c) Figure 4.17: Simulated and measured reflection coefficient, S 11 of cylindrical monopole plasma antenna. (a) Argon gas at 0.5 Torr. (b) Neon gas at 0.5 Torr. (c) Hg-Ar gas at 0.6 Torr. 101

124 Figure 4.17 exhibits the comparison between simulation and measurement results for reflection coefficient, S 11. The reflection coefficient, S 11 for Argon gas is measured at a frequency of 4.5 GHz with db and db at a frequency of 4.6 GHz during simulation. Meanwhile for Neon gas the reflection coefficient, S 11 for measurement is db at frequency 4.7 GHz and during simulation the reflection coefficient, S 11 at frequency 4.6 GHz is db. Meanwhile, the reflection coefficient, S 11 for Hg-Ar gas at frequency 4.74 GHz is db during simulation and db at frequency 4.8 GHz during measurement. On the other hand, for reflection coefficient, S 11 a small frequency shift that occurred between the measurement and the simulation is presumably due to the effect of flow of conduction current through the plasma element and will give effect to the plasma formation. However, in general, a good agreement has been achieved. Figure 4.18 (a) and (b) exhibits the comparison between simulation and measurement results for radiation pattern in polar plot for Argon and Neon gases when the cylindrical monopole plasma antenna is at a frequency of 4.6 GHz in E- Plane (phi=90 ) and H-Plane (phi=0 ) while Figure 4.18 (c) shows the comparison results between simulation and measurement for Hg-Ar gas tube at a frequency of 4.5 GHz in E-plane and H-Plane. The results show that the radiation patterns of cylindrical monopole plasma antenna in H-plane direction (at phi=0 o ) does not give significant effect in radiation pattern, thus the radiation patterns is obvious and can be observed in E-plane direction (at phi=90º). Nevertheless, the radiation pattern does not display the expected Omnidirectional shape and it might be due to the fact that when the electromagnetic wave arrived at the plasma region, the interaction between electromagnetic wave and plasma will changes the surface current distribution of plasma antenna, as it is known that the radiation pattern is determined by the surface current distribution of antenna. Thus, the shape for far-field radiation pattern of plasma antenna will be changed. However, good agreement between simulation and measurement has been achieved. 102

125 (a) (b) (c) Figure 4.18: Simulated and measured radiation patterns. (a) At frequency 4.6 GHz Argon gas in H-plane (left) and in E-plane (right). (b) At frequency 4.6 GHz Neon gas in H-plane (left) and in E-plane (right). (c) At frequency 4.5 GHz for Hg-Ar gas in H-plane (left) and in E- plane (right). 103

126 4.6 SUMMARY In this chapter, cylindrical monopole plasma antenna using argon gas, neon gas and Hg-Ar gas which consists of pressures 0.5 Torr, 5 Torr and 15 Torr have been described comprehensively. This chapter also includes a comparative analysis on the effects of several antenna parameters from the difference pressures and difference gases. From the analysis, it can be concluded that, when the pressure is increased, the electron density, n e also increases. From [76], the pressure of gas is directly proportional to the electron density, n e. Besides, the collision frequency, ν c also is pressure dependent, high pressures will increase the collision frequency, ν c [62]. As a result, the reflection coefficient, S 11 will deeper while the gain is decrease. Based on equation 3.38, when the value of collision frequency, ν c increase, the plasma conductivity, σ value will decrease. Consequently, this will influence the gain of antenna and the radiation pattern will change too. Thus from the analysis it can be concluded that the electron density, n e and collision frequency, ν c can influence the performance of antenna. In addition, the value of antenna gains also affected by size and mass of atom. When the size and mass of atom is increases, the gain will decrease. The results from measurements seem to agree well with the simulation results. Based on the measurement and analysis results, it can be concluded that, the cylindrical monopole plasma antenna with argon gas, neon gas and Hg-Ar gas (contained inside fluorescent tube) can be used to radiate radio signals. However the typical homemade plasma which only consist argon gas and neon gas required more complicated experimental apparatus, and therefore, it increased the complexity and the cost of realizing plasma antenna. Thus to design low cost plasma antenna and commercially available market plasma source, the fluorescent tube is a suitable option compared than neon and argon lamp. Therefore, in the next chapter, discussion will be focusing more on the design of plasma antenna as wireless transmission by using commercial fluorescent tube at 2.4 GHz frequency. Even though, based on analysis in this chapter, the frequency at 4.6 GHz will be used to design an antenna due to unavailability of material and limitation of technology to produce discharge tube with 104

127 2.4 GHz frequency. According to literature review [2-3], [38], [77], 4.6 GHz frequency will produce the same concepts analysis as same as 2.4 GHz frequency. 105

128 CHAPTER FIVE DEVELOPMENT OF MONOPOLE PLASMA ANTENNA USING FLUORESCENT TUBE FOR WIRELESS TRANSMISSION 5.1 INTRODUCTION Plasma antenna is a general term that represents the use of ionized gas as a conducting medium instead of a metal to either transmit or reflect a signal to achieve radar [76-77], or stealth or communication purpose [59]. There are many ways to generate plasma medium as a conductor element such as UV laser irradiation, or by laser initiated pre-ionization or by simply using commercial fluorescent lamp as a plasma antenna. In this work the commercial fluorescent lamp was chosen because it was low cost to produce plasma element. Besides that, by choosing fluorescent lamp as an plasma antenna, the complexity in building a homemade plasma tube as presented in [25], [80], [5], [81],[27] and [57] can be avoided. The typical homemade plasma tube provides more flexibility to change the plasma parameters by controlling the excitation power, type of encapsulated gas, pressure of gas, and also the density of the gas. However this method required more complicated experimental apparatus, and therefore, it increased the complexity and the cost of realizing plasma antenna. This chapter presents the investigation pertaining to monopole plasma antenna by using a commercial fluorescent tube and reviews the antenna performance as a transmitter and a receiver. As a comparison to the plasma antenna proposed in the literature review previously, the plasma antenna in this study was made from cylindrical shaped fluorescent lamp that functioned as a radiating element with target frequency at 2.4 GHz for Wi-Fi application. In this research work, 6500 K for color temperature, with 18 W was used as a plasma source. The commercial fluorescent lamp consisted of argon gas and mercury vapor with a diameter of 28 mm and a length mm. The brief introduction concerning the technology of fluorescent lamp is described in section 5.2. The parametric study and the effect the parameters to the antenna were studied and the results were compared. This part is presented in section 5.3. In section 5.4, the comparative results between metal antenna and plasma antenna 106

129 were investigated. Besides, the simulation and the measurement results are presented in section 5.5 to demonstrate the excellent performance of this antenna. Furthermore, in order to show that monopole plasma antenna with fluorescent lamp can react as a metal antenna, the experiment of radiation signal have been done in the Antenna Research Centre, Faculty of Electrical Engineering, Universiti Teknologi MARA. The results are presented in section MERCURY-ARGON (Hg-Ar) FLUORESCENT LAMP Most of the discharge lamps in use at the present time are the mercury-argon fluorescent lamps. A fluorescent lamp is a low-pressure mercury electric discharge lamp. It was discovered by a French physicist, Alexandre E. Becquerel in 1857, who investigated the phenomena of fluorescence and phosphorescence, as well as theorized the development of fluorescent tubes similar to those made today. Alexandre Becquerel experimented with coating electric discharge tubes with luminescent materials, a process that was further developed in later fluorescent lamps [82]. Some of the advantages of using fluorescent lamp are that their high performance in converting electrical power to light, size flexibility, and good color rendering properties that make them the most successful lamp product. Light is mainly produced by conversion of short wavelength UV radiation to visible radiation with the phosphor coating on the inner wall of the tube [83]. A typical hot cathode fluorescent lamp consists of a glass tube with its inner surface coated with fluorescent powder. It is filled with argon gas, a drop of mercury, and the filaments are tungsten wire electrodes coated with a thermionic emitter sealed into each end of the tube [84]. The rare gas argon is added to the lamp primarily to assist starting since the vapor pressure of mercury is very low initially. When current flows through the ionized gas between the electrodes, it emits ultraviolet (UV) radiation from the mercury arc. The UV radiation is converted to visible light by a fluorescent coating on the inside of the tube. The lamp is connected to the power source through ballast, which provides the necessary starting voltage and operating current. Figure 5.1 shows the construction of a fluorescent lamp. 107

130 Figure 5.1: Construction of the Fluorescent Lamp [85]. 5.3 PARAMETRIC STUDY ON A MONOPOLE PLASMA ANTENNA USING FLUORESCENT TUBE An inclusive parametric study on a monopole plasma antenna using fluorescent tube was conducted to identify the effects of various dimensional parameters, particularly in changing the dimensions of structure antenna. As initial requirements for monopole plasma antenna using fluorescent tube, the design was based on an operating frequency of 2.4 GHz. The dielectric tubes used in the simulation were made from lossy glass borosilicate (Pyrex) with permittivity at 4.82 and the thickness of the glass was 1 mm. The plasma was defined by using the Drude model (CST software) as mentioned in chapter 3. The schematic diagram of a monopole plasma antenna is shown in Figure

131 Figure 5.2: The structure of a monopole plasma antenna. Figure 5.2 shows the structure of a monopole plasma antenna using commercially available fluorescent tube which is the glass is from borosilicate (Pyrex) with permittivity at 4.82 with mm in length (L FT ) and diameter 28 mm (D FT ). The gas filled inside the fluorescent tube was argon gas and a drop of mercury vapor. The gas argon was added to the fluorescent tube to assist in starting since the vapor pressure of mercury is very low initially. Before the radiation began, the signals were connected to the tube with a coupler. This is called coupling sleeve. When the RF signals were applied to the coupling sleeve, the RF current flowed in the coil and generated an RF electric field. In addition, at the same time when the voltage was applied to the monopole plasma antenna, an electric field was produced and this electric field caused the current to flow in the plasma medium. The combination of current oscillated on the surface of the metal and this was caused by the disturbing currents in the interface between plasma and coupling sleeve. On top of that, these two electric fields were emitted from the monopole plasma antenna and propagated through the space [51-82]. Nonetheless, in this work, the coupling sleeve with a width W A of 18 mm was mounted 12 mm below at the lower end of the fluorescent tube. The coupling sleeve consisted of aluminum tape and copper wire. The copper wire was wrapped tightly at the aluminum tape. In this research work, the number of turns at the coupling sleeve had been 5. The function of coupling sleeve was to couple the 109

132 RF and the plasma element inside the fluorescent tube. The RF current from the network analyzer flowed in the coupling sleeve and generated an RF electric field to be coupled with the plasma column inside the discharge tube. Besides, the SMA connector was applied to maintain the 50 Ohms impedance for the RF generator. The power to energize the fluorescent tube was supplied by a set of electronic ballast with specification of V, 50-60Hz. The electronic ballast was chosen compared to magnetic ballast because electronic ballast is lighter in weight than magnetic ballast and it is more efficient compared to magnetic ballast [87]. Moreover, the length of plasma, diameter of plasma, number of turn of copper coil, diameter of copper wire, distance between coupling sleeve and SMA connector, and position coupling sleeve at the fluorescent tubes were optimized to obtain the best results. Besides, the effect of width of aluminum tape was also investigated for antenna performance. The parameters and dimension of the monopole plasma antenna are tabulated in Table 5.1. The comparative results of the proposed antenna performance are described and further discussed in terms of reflection coefficient, gain, VSWR, and radiation patterns. Table5.1: Parameters and dimension of monopole plasma antenna Parameter Label Dimension(mm) Length of monopole plasma antenna L FT Diameter of monopole plasma antenna D FT 28 Thickness glass t 1 Length of aluminum tape L A 30 Position Coupling Sleeve at the monopole plasma antenna L B 22 Distance from SMA connector to coupling sleeve L C 9 Width of aluminum tape W A 18 No of turns N 5 Diameter copper coil D C

133 5.3.1 Effects of the Length of Monopole Plasma Antenna. Figure 5.3 shows the reflection coefficient, S 11 results for simulated when optimized length plasma column from mm L FT mm with increment 40.0 mm. From simulation results clearly shows that when increase the length of plasma antenna the resonant frequency will shifted to the high frequency. However, when increase the length of plasma antenna, the plasma frequency also changes. Thus it will affect the resonant frequency of the antenna. This behavior indicates that the resonant frequency of plasma antenna can be achieved by controlling the plasma frequency. Hence, this analysis proved that, the length of monopole plasma antenna has a greater influence on the operating frequency. 2.4GHz = dB Figure 5.3: The effects on reflection coefficient, S 11 due to change of length monopole plasma antenna. 111

134 5.3.2 Effects of Diameter Plasma Antenna The effect of the diameter on fluorescent tube has been analyzed to observe which value gives the better result. The diameter of plasma antenna are varies from 20 mm until 36 mm with an increment of 4 mm. From Figure 5.4 shows that, the reflection coefficients, S 11 fluctuated when the diameter of the plasma column was varied. It was because; when the diameter of plasma antenna was changed, the electron density of plasma changed as well. Thus, it influenced the performance of the antenna. From the observation, the best result providing good impedance at 2.4 GHz was obtained when the diameter was 28 mm with s- parameter was equal to db. Hence, 28mm was chosen for the final design. 2.4GHz = db Figure 5.4: The effects on reflection coefficient, S 11 due to change of the diameter of plasma antenna Effects of Parameter for coupling sleeve. In contrast to conventional metallic antennas, it is impossible to make a direct electrical contact with the plasma conductor because the plasma is encapsulated in a dielectric tube. For that reason, it was necessary to use capacitive coupling to launch surface waves as a way to radiate radio signals. As mentioned in section 5.3, the plasma antenna needed a coupler to transmit and to receive signals. Only a small portion of monopole plasma antenna was covered with coupling sleeve. The structure of coupling sleeve as shown in Figure

135 Figure 5.5: Coupling sleeve structure. To design coupling sleeve, some parameters such as the width of aluminum, the position of coupling sleeve to the plasma antenna, the diameter of coil, the number of turns in coupling sleeve, the distance between SMA connector to the coupling sleeve, were taken into consideration. 2.4GHz = dB 2.4GHz = dB (a) (b) 2.4GHz = dB 2.4GHz = dB (c) (d) 113

136 2.4GHz = dB (e) Figure 5.6: Effects on reflection coefficient of parameter for coupling sleeve. (a) Numbers of turns. (b) Width of aluminum tape. (c) Position of coupling sleeve. (d) Diameter of coil. (e) Distance between SMA connector to coupling sleeve. The numbers of turns of the coupling sleeve have been optimized to identify if it affected the performance of the antenna. However, from this analysis, the number of turns in coupling sleeve give minimum effect to the reflection coefficient as illustrates in Figure 5.6 (a). In this analysis, the number of turns were varies from 3 to 8 turns. Figure 5.5(b) depicts the simulated results with varied width of aluminum tape. W A was simulated in four, which varied from 16 mm to 22 mm with 2 mm of increments. From Figure 5.5 (b), it was found that when the width of aluminum tapes increase, the S 11 slightly shifted to the left. From this analysis, the optimum reflection coefficient at operating frequency of 2.4 GHz when the aluminum tape equal to 18mm ( db). Another parameter that had to be analyzed was the position of coupling sleeve to the monopole plasma antenna; L B. Figure 5.5(c) exhibits the simulated result for reflection coefficient when the distance from the bottom of the monopole plasma antenna to the coupling sleeve is varied from 2 mm L B 290 mm. Besides, from Figure 5.5 (c) depicts that, when increase the position of coupling sleeve the operating frequency shifted to the upward. In addition, the best result providing a good impedance matching at 2.8 GHz is obtained when L B is 22 mm with S 11 at db. Hence, this position of coupling sleeve was chosen for the final design Meanwhile, Figure 5.5(d) shows the comparison results of different copper coil diameters, D C for coupling sleeve from 0.1 mm until 1.3 mm with an increment of 0.4 mm. From the simulation results, it is observed that the 114

137 reflection coefficient results are slightly shifted to the downward when the diameter of copper coil increases. The diameter coil of 0.5 mm give the best result at an operating frequency of 2.4GHz (-43.29dB). Thus, the final design for copper coil is 0.5 mm. Another parameter that affected the targeted operating frequency is the distance between coupling sleeve to the SMA connector, L C as shown in Figure 5.5 (e). The effect in s-parameter, S 11 is observed when L C is varied from 7 mm to 11 mm with an increment of 1 mm. Moreover, the results from the analysis showed that the operating frequency shifted to a lower frequency. Hence, the function of L C as a transmission line that connected the plasma medium to the RF signal and carried the electromagnetic wave which was needed to minimize reflections and power loss. Thus, the increase in L C caused more losses in plasma antenna and signal reflection. From this analysis, the optimum result at a frequency of 2.3 GHz with s-parameter is db. However, the targeted operating frequency in this research is 2.4 GHz, so that the appropriate L C is equal to 9mm with reflection coefficient, S 11 = db. In general, from this analysis, the parameter of coupling sleeve doesn t to influence the performance of antenna in terms of operating frequency. 5.4 ANALYSIS BETWEEN MONOPOLE PLASMA ANTENNA AND METAL ANTENNA As mentioned in chapter 2, the plasma element can transmit and receive radio frequency same as metal element such as copper wire and copper rode when the plasma frequency is much greater than operating frequency [84-85]. Thus, in this part, the comparison of antenna performances between monopole plasma antenna and metal antenna is presented. Metal antenna was designed to be identical to the monopole plasma antenna. Besides, it is very essential to observe the condition of monopole plasma antenna during ON and OFF condition. 115

138 Figure 5.7: Comparison of simulation results of reflection coefficient,s 11 between metal antenna, condition during plasma OFF and ON. Three condition of antenna were simulated; monopole plasma antenna (plasma ON), metal monopole antenna and the condition when plasma OFF. Figure 5.7 shows the comparison results between monopole plasma antenna by using fluorescent lamp during condition plasma antenna ON, plasma antenna OFF and metal monopole antenna. As depicted in Figure 5.7 the reflection coefficient, S 11 of monopole plasma antenna during ON state at frequency 2.4 GHz is db while for OFF state at 2.4 GHz is db. For metal antenna are db at operating frequency of 2.46 GHz. From this analysis, when monopole plasma antenna in OFF state, the reflection coefficient, S 11 is more than -10 db ( db) while when monopole plasma antenna in ON state the reflection coefficient, S 11 is less than -10 db at frequency 2.4 GHz which is show good impedance matching. Thus it proof that during plasma ON it can become as conductor element like a metal antenna while during OFF condition it become as a dielectric. Figure 5.8: VSWR for plasma antenna on, off and metal antenna. 116

139 Figure 5.8 shows the voltage standing wave ratio (VSWR) against frequency (GHz) during plasma ON, plasma OFF and metal antenna monopole results. From the simulation the value of VSWR during plasma ON state is 1.01 and for metal antenna is 1.18 at frequency 2.4 GHz while during plasma OFF state is From this comparison shown that, the plasma antenna during ON state have a perfectly matched to the antenna s impedance same with conventional metal antenna. However during plasma OFF, the value of VSWR is greater than 2. The antenna can be described as having a good match when have a VSWR value under 2 and was considered as suitable for most antenna applications. Thus, when plasma OFF, the antenna behaves as a dielectric. Figure 5.9 : Simulated radiation patterns of plasma monopole antenna during ON and metal antenna in polar plots in the E-plane (phi = 90 ). Figure 5.9 displays the radiation pattern E-plane (phi=90 ) for plasma antenna during ON state and metal antennas. It is obvious that, the radiation patterns when plasma antenna ON was quite similar to the metal antenna. The gain of plasma antenna is dbi and metal antenna is dbi. The gain of plasma antenna during ON is lower compare than metal antenna due to the much lower conductivity of the plasma compared with the metal antenna. 5.5 SIMULATION AND MEASUREMENT RESULTS Figure 5.10 exhibits the comparison between simulation and measurement results of reflection coefficient, S 11 for the monopole plasma antenna using fluorescent tube. The measured results indicated that the antenna was capable in operating at 2.4 GHz. The simulated result during plasma ON is db at frequency 2.4 GHz while 117

140 for measured result the reflection coefficient, S 11 at 2.4 GHz is db. Result measurement for reflection coefficient, S 11 during plasma OFF at frequency 2.4 GHz is db. This is shown that, during plasma OFF there is no conductor element and as a result cannot performance as an antenna. From Figure 5.10, the measured result seems to have lower value of S 11 than simulated result at frequency 2.4 GHz is presumably due to the parasitic effect from imperfect solder between SMA connector and coupling sleeve. Besides, the difference between simulation and measurement might be due to the current flow to fluorescent tube that might not be consistent and affected the condition of plasma produced in the real experiment. However, in general, a good agreement has been achieved between simulation and measurement. Figure 5.10: Simulated and measured reflection coefficient, S 11 for monopole plasma antenna. Apart from that, the radiation patterns of monopole plasma antennas during ON were observed in both simulated and measured scenarios. The measured and simulated radiation patterns at E-plane (phi=90 ) for the monopole plasma antenna excited at 2.4 GHz are shown in Figure The results show that the radiation patterns of cylindrical monopole plasma antenna in H-plane direction (at phi=0 o ) does not give significant effect in radiation pattern, thus the radiation patterns is obvious and can be observed in E-plane direction (at phi=90º). Good agreement and well behaved radiation patterns were obtained. This was attributed to the omni-directional characteristics of monopole plasma antenna. In comparison, the measured scenarios displayed some distortions in terms of radiation 118

141 pattern which were due to losses and connectivity impurities. Besides, the cross-polar radiation pattern is lower than -10 dbi. (a) (b) Figure 5.11: Simulated and measured radiation patterns of monopole plasma antenna (ON) at 2.4 GHz in (a) H-Plane and (b) E-Plane. 5.6 WIRELESS SIGNAL TRANSMISSION EXPERIMENT In this section, the experiment radiation signal is presented. To prove that monopole plasma antenna with fluorescent tube is working, the experiment radiation signal were conducted. For the first experiment, the main objective is to prove that the received signal is come from plasma antenna not from coupling sleeve. After that, the second experiment is to show that plasma monopole antenna can served as a transmitter and the third experiment as a receiver. The experiments concerning signal strength for plasma monopole antenna are also presented in this section Experiment Radiation Signal The aim of this experiment was to determine that the source of signal generated is transmitted from plasma antenna and not coupling sleeve. The signal that is produced can be detected by using Wi-Fi analyzer software that can be easily installed in smart phone. The Wi-Fi analyzer is software develops in which main functions are to test and observe the signal strength of an antenna. From this experiment, three conditions of plasma antenna were being tested to show that generated and transmitted signal is come from plasma antenna and not from coupling sleeve. In first condition, coupling sleeve was uncovered with aluminumwrapped shielding box and fluorescent tube was switched ON, the result shows that strength of signal from plasma antenna is higher as compared other signals (red line 119

142 represent Plasma Antenna UiTM S.Alam ). For second condition, the coupling sleeve was covered with aluminum-wrapped shielding box and fluorescent tube lamp was switched ON.The result shows signal generated from plasma antenna is the same with first condition tested which is higher compared other signals. This proves that the received signal was generated and transmitted from plasma antenna because even though the coupling sleeve was covered with aluminum-wrapped shielding box, still signal was traceable. For third condition, the coupling sleeve was again covered with aluminum-wrapped shielding box and fluorescent tube was switched OFF. Result from third condition shows that the signal strength transmitted to Wi-Fi analyzer has dropped to low signal. Thus, from this experiment it is proven that the signal was came from plasma antenna. Table 5.2 shows the summary results for three conditions. Table 5.2: Summary results signal strength for three conditions. Condition Signal Strength Conclusion Signal strength good 1 st : Coupling sleeve was not covered with aluminum-wrapped shielding box and fluorescent tube was switched ON. Signal strength good 2 nd : Coupling sleeve was covered with aluminum-wrapped shielding box and fluorescent tube was switched ON 120

143 Signal strength weak 3 rd : Coupling sleeve was covered with aluminum shielding box and fluorescent tube was switched OFF Monopole Plasma Antenna as a Transmitter In experiment 2, monopole plasma antenna with fluorescent tube was set to serve as a transmitter. Besides, a spectrum analyzer was used to observe the received frequency spectrum, to analyze if the plasma antenna worked properly as a transmitter. The measured signal at the receiver is shown in Figure The result showed a peak signal at 2.4 GHz, which matched the transmitting signal from the RF generator. The peak rose approximately 15 db above the noise floor. The captured signal frequency was within the operating frequency range of the constructed plasma monopole antenna, which had been confirmed in the previous return loss measurement experiment. This proved that this antenna could transmit information at that frequency. Meanwhile, Figure 5.13 shows that there was no peak signal when the RF generator was turned off. This indicated that the captured signal originated from the RF generator in the experimental setup. Figure 5.12: Captured signal when plasma antenna serves as transmitter. 121

144 Figure 5.13: Noise floor when the RF generator is turned off Monopole Plasma Antenna as a Receiver Meanwhile, experiment 3 observed the functionality of the energized fluorescent tube as a receiver. The signal transmitted from the reference antenna at the transmitter was captured by the energized fluorescent tube, and was observed by the spectrum analyzer. Figure 5.14 shows that the signal was captured at 2.4 GHz, which matched the transmitting signal s frequency of the RF generator. Similar to the previous experiment, the peak rose more than 20 db above the noise floor. Besides, Figure 5.15 shows the result of signal received when the fluorescent tube was deenergized and removed from the receiving system. In this case, no peak signal was observed from the graph since the plasma antenna was de-activated and removed from the system. Figure 5.14: Captured signal when plasma antenna serves as receiver. 122

145 Figure 5.15: Noise floor when the plasma antenna was removed from the receiver system Signal Strength for Monopole Plasma Antenna Figures 5.16 and 5.17 represent the signal strength results of Wi-Fi channel in communication laboratory. These results were measured using Wi-Fi Analyzer applications. From the results, red line refers to the result of plasma monopole fluorescent tube antenna named Plasma Antenna UiTM S.Alam, while the blue and the green lines represent other signal strength that come from other Wi-Fi channels in the same room. Figure 5.16 shows the performance of signal strength when the AP router was connected to the fluorescent tube antenna. It proved that the antenna worked properly and possessed good signal strength, which was approximately 45 dbm. Meanwhile, Figure 5.17 shows the result of signal strength when the fluorescent tube antenna was removed from the AP router. The signal dropped about 40 db, which means that the signal was not radiated and was very weak. 123

146 Figure 5.16: Performance of Signal Strength when the fluorescent tube antenna was connected to the AP Router. Figure 5.17: Performance of Signal Strength when fluorescent tube antenna disconnected from AP Router. 5.7 SUMMARY In this chapter, the simulation and the measurement results of plasma antenna showed that a simple fluorescent tube, used for household applications, can be used to work as a plasma antenna for Wi-Fi application. This could be done by implementing the coupling technique by applying AC voltage 240 V across the electrodes of fluorescent tube. In this research work, the plasma antenna was fabricated by using commercial fluorescent tube with a length of mm and a diameter of 28 mm, as well as being measured at frequency 2.4 GHz. 124

147 Besides, the measurement showed that the radiation patterns of the plasma antennas measured at frequency 2.4 GHz had been quite similar to the radiation pattern of classic monopole metal antenna. Thus, the findings obtained from this study indicated that the plasma antenna could be considered as a monopole antenna. Besides, the plasma antenna prototype yielded reflection coefficient, S 11 < -10 db, which was suitable for indoor wireless transmission applications. In addition, the results from measurements of each structure seemed to agree well with the simulation results. Therefore, the commercial fluorescent lamp has the potential to be used as a good conductor element and it is also a low-cost plasma antenna. Further research with the application of commercial fluorescent lamp as a reflector element is presented in the next chapter. 125

148 CHAPTER SIX DEVELOPMENT OF RECONFIGURABLE PLASMA ANTENNA ARRAY 6.1 INTRODUCTION Reconfigurable antennas have attractive a number of features, such as the ability to reconfigure themselves autonomously to adapt to the changes or with the system to perform entirely different functions. The reconfigurable antenna is also capable of providing a single antenna for use with multiple systems. Mostly, in reconfigurable antennas, the antennas are constructed by using metallic elements, along with active devices. These active devices are employed to provide switching mechanism for the antennas to steer beam in particular directions. However, this chapter discusses and explains the plasma medium as reconfigurable antennas instead of using metallic antenna. As mentioned earlier, plasma elements have a number of potential advantages over conventional metal elements for antenna design as they permit electrical, rather than physical control as their characteristics. Moreover, antenna arrays can be rapidly reconfigured without suffering perturbation from unused plasma elements. Thus, it can offer extra advantage to reconfigure antenna compared to metallic antenna without using active devices. In this chapter, the behaviors of the reconfigurable plasma antenna array were studied and applied to the design of a new antenna. 6.2 RECONFIGURABLE PLASMA ANTENNA ARRAY A new structure of a reconfigurable plasma antenna array was constructed by using commercial fluorescent lamp at an operating frequency of 2.4 GHz. The fluorescent tube functioned as a plasma element and the reason for selecting a commercial fluorescent lamp as plasma element has been discussed in the previous chapter. Likewise, the development of the plasma antenna with fluorescent lamp has 126

149 been proved and explained in previous discussion. It has also been demonstrated previously that fluorescent lamp can be used as a radiating element. This shows that fluorescent lamp has the ability to function like a metal element and at the same time, it can behave like a reflector element. In contrast to conventional antennas that produce fixed directional radiation patterns, the reconfigurable plasma antenna array studied here had been capable of steering the beam pattern over 360 of freedom. The main objective of this work was to design, to analyze, and to develop a reconfigurable antenna by using plasma element with the capabilities of beam scanning and beam shaping. The characteristics of the antenna radiation were simulated using the CST Microwave Studio. Both simulation and measurement results are discussed in this section Reconfigurable Plasma Antenna Array Structure To simulate the performance of an antenna design, CST MWS software was used. The structure of the proposed antenna is shown in Figure 6.1(a), (b), and (c). The reconfigurable plasma antenna array structure consisted of 12 tubes of commercial cylindrical shaped fluorescent tubes that contained the mixture of mercury vapor and argon gas. The ground was circular aluminum with a thickness of 3 mm and radius of 105 mm. The height of each plasma tube from the ground plane surface, L PA is 288 mm and its diameter is 16 mm. Meanwhile, the energy source was supplied by a monopole antenna that resonated at 2.4 GHz located at the center of the ground plane. Besides, the height of the monopole antenna is 35 mm with a diameter of 3 mm. Moreover, the antenna was fed by a standard SMA connector that was located in the middle of the ground. The probe feed (coaxial feed) is a technique that was used in this project for feeding microstrip patch antennas, fed by a SMA connector. The SMA connector was designed based on the specification by using Teflon with dielectric constant = The impedance of feeding coaxial transmission line is 50 Ω. The tubes used in the simulation were made from lossy glass borosilicate (Pyrex) with a permittivity = Meanwhile, the tube wall (glass) has a thickness, t = 0.1 mm. The distance between the monopole antenna and the fluorescent tubes, D BB is equal to 75 mm, whereas the angle between the centers of the two adjacent elements is 30º. The 127

150 parameter and dimension of reconfigurable plasma antenna array is presented in Table 6.1. (a) (b) z y x (c) Figure 6.1: Geometry of the reconfigurable plasma antenna array. (a) Top view. (b) Side view. (c) Overall structure. 128

151 Table 6.1: Parameters and dimension of reconfigurable plasma antenna array. Parameter Label Dimension(mm) Space gap between plasma elements D AA 36 Distance between plasma element to monopole antenna D BB 70 Aluminum ground plane radius D CC 105 Aluminum ground plane thickness t 3 Length of plasma element L PA 288 Diameter of plasma element D PA 16 Length of monopole antenna L M 35 Diameter of monopole antenna D M 3 Angle between two adjacent plasma elements θ ANALYSIS OF RECONFIGURABLE PLASMA ANTENNA ARRAY In this section, the effects of distance between monopole antenna and fluorescent tubes, D BB towards radiation patterns of reconfigurable plasma antenna array had been investigated. The results of return loss were also presented to ensure that the effects took place at the desired frequency mode. Besides, the target frequency band was 2.4 GHz Effects of Distance between Monopole Antenna to Fluorescent Tube, D BB Figure 6.2 shows simulation result of reflection coefficient, S 11 on the effect of different distances between monopole antenna to fluorescent tube, D EE. The distance between monopole antenna and fluorescent tube had been varied from 50 mm until 80 mm with an increment of 10 mm. As depicted in Figure 6.2, it clearly shows that the distance between monopole antenna to fluorescent tube, D BB has significant effects on return loss and resonant frequency. The best result for the antenna to operate at a frequency of 2.4 GHz is when D EE = 70 mm. 129

152 Figure 6.2 : The effect of distance between monopole antenna to fluorescent tube. In this analysis, the peak gain is an important element that contributes to the good performance of reconfigurable plasma antenna array. Figure 6.3 shows the comparison of simulated gains when the D EE is varies at operating frequency of 2.4 GHz. The gain value is referred as theta gain, at theta =50 o. Highest gain is achieved when the value of D EE value is 70 mm. Figure 6.3 Comparison of simulated gains at frequency 2.4 GHz in H-Plane. 130

153 (a) (b) Figure 6.4: Comparison of radiation patterns in polar-plot in (a) E-plane and (b) H-plane. Figure 6.4 shows the simulation results of radiation patterns with respect to different distances between monopole antenna to fluorescent tube, D EE at frequency 2.4 GHz in E-plane and H-plane at ϕ=50. The results show that the radiation patterns of reconfigurable plasma antenna array in H-plane direction (at ϕ= 50 o ) give more significant effect in radiation pattern compared the radiation patterns in E-plane direction. As clearly shown in Figure 6.4, when D EE is 80 mm the beam is more focus and this lead to high directivity. However the back lobe of D EE is higher as compared when D EE is 50 mm, 60 mm and 70 mm respectively. The results also indicate that the back lobes of D EE = 50 mm and D EE = 60 mm are smaller than 70 mm but having lower gain comparing to D EE = 70 mm. Thus the best optimize for distance between monopole antenna to fluorescent tube, D BB is 70 mm Effects of Thickness of Ground, t. As depicted in Figure 6.1, the structure of reconfigurable plasma antenna array consisted of ground aluminum. A parametric analysis was conducted to attain the optimum performance of antenna. In this parametric analysis, the effect on S 11 has been investigated at frequency 2.4 GHz. The thickness ground, t was varied from 2 mm to 5 mm by a constant increment of 1 mm. Figure 6.5 illustrates the effects in S 11 when t is varied. The optimum result for S 11 is when t is equal to 3 mm. 131

154 Figure 6.5: Effect on S 11 when t is varied Effect of Length of Monopole Antenna. L M. Figure 6.6: Effect on reflection coefficient, S 11 and resonant frequency when L M is varied. In this case, the effect of length of monopole antenna, L M on return loss and resonant frequency were investigated. The design of the antenna is illustrated in Figure 6.1(c). As depicted in Figure 6.6, it clearly shows that the length of monopole antenna, L M has significant effect on return loss and resonant frequency. From the result in Figure 6.6, L M = 35 mm is chosen so that the antenna is expected to operate at a frequency of 2.4 GHz. 132

155 6.3.4 Effects of the Numbers of Fluorescent Tubes and Adjacent Angle, θ. In this section, the effect of the numbers of fluorescent tubes and adjacent angle, θ has been investigated. Changing the numbers of fluorescent tubes will also change the adjacent angle between the two plasma elements, θ. Figure 6.7 explains the relationship between the number of fluorescent tubes and adjacent angle. (a) (b) (c) Figure 6.7: Relationship between the number of fluorescent tubes and adjacent angle. (a) 10 fluorescent tubes were used with only 6 elements activated (b) 12 fluorescent tubes were used with only 7 elements activated (c) 20 fluorescent tubes were used with only 15 elements activated. In Figure 6.7 shows the different number of fluorescent tubes are use as compared in figure (a),(b) and (c).figure 6.7(a) will give greater adjacent angle (θ =36 ) than figure 6.7(b) = (θ=30 ) and 6.7(c) = (θ= 18 ). Hence, when increase the number of fluorescent tubes, the angle between the two adjacent fluorescent tubes will decrease. (a) (b) Figure 6.8 : Simulated radiation pattern in polar plot in (a) E-Plane and (b) H-plane. 133

156 Figure 6.8 exhibits the simulated co-polarization of reconfigurable plasma antenna array in polar plot E-plane and H-plane at frequency 2.4 GHz. The plots were based on the radiation patterns which were cut based on E-plane and H-plane. The reason why cut in H-plane because it give more significent effect and can observe maximum gain at H-plane compared the radiation patterns in E-plane direction. Figure 6.9 illustrates the changes in s-parameter, S 11 when the number of elements and the adjacent angle, θ were varied. Based on this analysis, the best number of elements and adjacent angle, θ so that the reconfigurable plasma antenna array can be operate at frequency 2.4 GHz is when θ is 30 and the number of elements is 12. Meaning that, number of deactivated elements (switched OFF) is 5. On top of that, Table 6.2 shows the summary of the performances concerning the analysis of the number of element and the angle between the two adjacent elements. In the performance analysis based on table 6.2, the deactivation of elements was made different in each sequence. Reason behind this decision is to get a sequence that can produce a symmetrical main lobe radiation pattern. Figure 6.9: Simulation reflection coefficient, S 11. Table 6.2 The performances analysis of the number of element and the angle between two adjacent elements. Number of No of Angle HPBW( ) Side Gain (db) Reflection elements deactivated elements (switched OFF) between two adjacent elements, θ lobe level (db) coefficient, S 11 at 2.4 GHz (db)

157 Effects of Fluorescent Tubes on Radiation Pattern In order to observe the effects of fluorescent tubes on radiation pattern, the design model has been simulated and measured by two conditions; i) Monopole antenna without fluorescent tubes, and ii) Monopole antenna surrounded by fluorescent tubes (plasma OFF) (a) (b) Figure 6.10: Simulation and measurement results for radiation pattern in H-plane (right) and E-plane (left). (a) Plasma off. (b) Monopole antenna only. As depicted in Figure 6.10, simulated radiation patterns in polar plots are compared with the measurement results in H-plane and E-plane for two conditions. 135

158 The radiation pattern in H-plane give more significent effect and can observe maximum gain at H-plane compared the radiation patterns in E-plane direction. The results shows for both conditions are quite similar radiation pattern in polar plot. Hence, both simulated and measured results can be considered as to have good agreement. The gain of the monopole antenna and the plasma off were also compared as shown in Figure 6.11 for the simulation result. Nonetheless, there was not much reduction in gain with the presence of the surrounding dielectric tubes. Figure 6.11: Comparison between monopole and plasma off for simulation results gain (db) versus frequency (GHz). These results again confirm that, the presence of dielectric tubes surrounding the monopole antenna has no significant effects to the reflection coefficient. Therefore, it is possible to construct a reconfigurable reflector antenna by only activate and de-activate the plasma elements without having to worry about the effect of fluorescent tubes. 6.4 SWITCHING PATTERN OF RECONFIGURABLE PLASMA ANTENNA ARRAY FOR BEAM SCANNING The concept of creating a reconfigurable plasma antenna array is the energy source surrounding a plasma blanket in a region where the plasma frequency is less than the antenna frequency, whereby the antenna radiation passes through the blanket while in the region, whereby the plasma frequency is higher than the antenna 136

159 frequency, and the plasma behaves like a perfect reflector. Thus, to create a beam shaping radiation pattern, not all elements were set as plasma or metal in every simulation. Generally, a number of deactivated elements (switched OFF) defined and determined the size of beamwidth of the radiation pattern. As the idea is to have a sectoral beam shape, only certain of the total elements are working as reflector at a time (switched ON). Hence, in order to determine the numbers of plasma element to switch OFF is needed, the analysis of switching scheme was investigated. In this research, the antenna prototype used 12 plasma elements to control its element state (ON or OFF) in order to shape the main beam. Since each elements can be controlled individually, the antenna has huge possibility to shape its beam. Figure 6.12 shows the sequence of the elements by numbering in clockwise rotation accordingly to a specific electronic switch. Figure 6.12: Switching numbering for reconfigurable plasma antenna array. In this research work, the set up of three configurations had been identified. First was 1/12 (1 fluorescent tube switched OFF and 11 fluorescent tube switched ON), second was 3/12 (3 fluorescent tube switched OFF and 9 fluorescent tube switched ON), and the last one was 5/12 (5 fluorescent tube switched OFF and 7 fluorescent tube switched ON), elements deactivated. Figure 6.13 shows the simulated results reflection coefficients, S 11 for switching pattern of reconfigurable plasma antenna array. From this figure, the reflection coefficients, S 11 for configuration for 3/12 ( db) and 5/12 operate ( db) at 2.4 GHz while for configuration 1/12 the magnitude of reflection coefficients, S 11 is db at resonant frequency 2.2 GHz. 137

160 Meanwhile, Figure 6.14 illustrates the measured result reflection coefficients, S 11 for switching pattern of reconfigurable beam switching plasma antenna array. From this figure, the measured result for configuration for 1/12 seems to have a slight frequency shift to the left and lower value of S 11 than of the simulated. The reflection coefficients, S 11 is measured at 2.0 GHz with db and measured reflection coefficients, S 11 for configuration 3/12 the resonant frequency shifted to the right (2.66 GHz) with db. As for configuration 5/12 the measured result at 2.4 GHz is db which is slightly lower compared to the simulation result. Besides, during all plasma off the measured result for reflection coefficients, S 11 equal to db at frequency 2.33 GHz. Figure 6.13: Simulated reflection coefficients, S 11 for switching pattern of reconfigurable plasma antenna array. Figure 6.14: Measured reflection coefficients, S 11 for switching pattern of plasma antenna array. 138

161 (a) (b) Figure 6.15 : Simulated radiation pattern at 2.4 GHz for switching pattern of reconfigurable plasma antenna array (a) in H-plane and (b) in E-plane. (a) (b) Figure 6.16: Measured radiation pattern at 2.4 GHz for switching pattern of reconfigurable plasma antenna array (a) in H-plane and (b) in E-plane. Moreover, a few simulations were performed in order to obtain good radiation pattern. As mentioned before, the number of deactivated elements (switched OFF) will determine the beamwidth of radiation pattern. As illustrated in figure 6.15, the configuration of 1-element resulted in omni-directional and does not give influence in getting beam shaping pattern. Besides, the pattern of radiation pattern for configuration 1-element is quite similar when all plasma is deactivated (switched OFF). Figure 6.16 shows the measured result of radiation pattern for switching pattern of reconfigurable plasma antenna array in H-plane and E-plane at 2.4 GHz. The maximum gain of reconfigurable plasma antenna array can be obviously seen in H- plane direction (at ϕ =50º). 139

162 (a) (b) Figure 6.17 : Simulated result for different number of elements in H-plane (ϕ =50 ) (a) Gain in dbi (b) Directivity in dbi. Nonetheless, wider beam shape at broadside direction is observed when 3- elements configuration is deactivated (switched OFF) but the gain (12.39 dbi) and directivity (12.74 dbi) is lower compared to 5-elements configuration as shown in Figure 6.17(a) and (b). It is due to broadening radiation effect. Additionally, configuration of 3-elements shows higher side lobe and back lobe values as compared to 5-elements configuration. Thus give the gain and directivity lower than 5-elements configuration. 140

163 Therefore, from these analyses pertaining to radiation pattern, with the optimized reconfigurable beam switching plasma antenna array, the 5-elements configuration provides the radiation pattern at an optimum result. The beam is more focus while the back lobe and side lobe are lower as compared to 1-elements and 3- elements configuration and also giving the highest gain (13.04 dbi) and directivity (13.17 dbi). Thus, there are only 5 elements need to deactivate (switched OFF) at the same time in order to scan the beam from 0 until 360 degree with target increment every 30 and the balance is in activate (switched ON). Table 6.3 shows the summary of switching pattern of reconfigurable plasma antenna array for gain (dbi) and Directivity (dbi). Table 6.3: Summary of switching pattern of reconfigurable plasma antenna array for beam scanning. Number of configuration Gain(dBi) Directivity(dBi) 1/ / / / / In this investigation, 12 sequences with the optimized reconfigurable plasma antenna array were analyzed. The sequences are listed in Table 6.4 along with its corresponding switching setting. Table 6.4: Switching setting for reconfigurable plasma antenna array (Blue color represent activated elements ( switched ON), while white color represent deactivated elements (switched OFF)). Number of Design Deactivated elements Activated elements sequence (Switched OFF) (Switch ON) 1 10,11,12,1,2 3,4,5,6,7,8,9 2 11,12,1,2.3 4,5,6,7,8,9,10 141

164 3 12,1,2,3,4 5,6,7,8,9,10,11 4 1,2,3,4,5 6,7,8,9,10,11,12 5 2,3,4,5,6 7,8,9,10,11,12,1 6 3,4,5,6,7 8,9,10,11,12,1,2 7 4,5,6,7,8 9,10,11,12,1,2,3 8 5,6,7,8,9 10,11,12,1,2,3,4 9 6,7,8,9,10 11,12,1,2,3,4,5 10 7,8,9,10,11 12,1,2,3,4,5,6 142

165 11 8,9,10,11,12 1,2,3,4,5,6,7 12 9,10,11,12,1 2,3,4,5,6,7,8 As explained in the previous section, the concept of reconfigurable plasma antenna array when the fluorescent tube is de-activated or plasma OFF state, the radiation signal from the monopole antenna will escape from the plasma blanket and when the fluorescent tube is activated or plasma ON state, the radiation signal will be trapped inside the plasma blanket. Thus, to control the radiation signal at which angle it will escape, some features were added to the original design to create a user-friendly device, as the main target is to ease users with the system usage. The system was operated by using Arduino technology system, whereby users can use a remote to control, which is the fluorescent tube, when they want to deenergized (OFF state) or energized (ON state). This allows the user to focus the signal at their desired angle. As shown in Figure 6.18, this system consisted of 2 black boxes. One functioned as a transmitter (remote control) and the other functioned as a receiver. As illustrate in Figure 6.19, the receiver box was connected to the antenna. Moreover, the signal transmitted from the transmitter box can go up to 10 meters. Figure 6.18: Remote control and receiver. 143

166 Figure 6.19 : Photograph of the overall structure of reconfigurable plasma antenna array integrated with Arduino technology. On the other hand, Figure 6.20 illustrates the components that make up a remote. Each component has its very own function to assist in the operation of reconfigurable plasma antenna. LCD or liquid-crystal display function as a panel display to display images indicates the response to the command entered. The main switch is the component that controls to ON and OFF the remote control. Next, is the LED or light-emitting diode that functions to indicate which fluorescent tube is in ON or OFF position. The configuration of the fluorescent tubes is portrayed in Figure Last but not least, the keypad switch functions to make selection of which fluorescent tube to be turned ON or off. Switches 1 until 9 represent fluorescent tubes 1 until 9 with clockwise rotation, while switches A, B, C, # and * represent numbers 10, 11, 12, all OFF, and all ON respectively.. Figure 6.20 : Remote control with the main components. 144

167 (a) (b) Figure 6.21: (a) Circuit at the remote control. (b) Circuit at the receiver. 6.5 SIMULATION AND MEASUREMENT RESULTS OF RECONFIGURABLE PLASMA ANTENNA ARRAY The process of simulation and optimization of reconfigurable plasma antenna array was performed by using CST Microwave Studio. The prototype of reconfigurable plasma antenna array was successfully fabricated and measured in order to validate the simulated results. The antenna performance was analyzed in terms of return loss and its radiation characteristics, including gain, side lobe level, HPBW, and main lobe direction. To achieve the pattern of reconfiguration, diversity in the main lobe directions had been the main focus in this antenna design.. (a) (b) Figure 6.22 : Schematic drawing of reconfigurable plasma antenna array. (a) Overall view (b) Side view. 145

168 (a) (b) Figure 6.23: Prototype of the reconfigurable plasma antenna array (a) De-activated (Plasma off) of 12 fluorescent tubes. (b) 5/12 plasma in ON condition Figure 6.22 shows the schematic diagram of the fabricated reconfigurable plasma antenna array from overall view and side view of the antenna. The prototype of reconfigurable plasma antenna array is shown in Figure In order to steer a beam from 0 to 360, only 5 elements were need to be deactivated (Switched OFF) while the rest remained activated (ON state). To ease the scanning process, each element was numbered by its location in clockwise direction as shown in Figure The ON-OFF sequences to scan were made based on the switching setting scheme listed in Table 6.3 which has been explained in the earlier section (switching scheme). The simulated reflection coefficient, S 11 is shown in Figure The results indicated that the patterns for reflection coefficient, S 11 were quite similar for all angles at frequency 2.4 GHz. Figure 6.24 : Simulated of reflection coefficient, S

169 The pattern reconfiguration of reconfigurable plasma antenna array can be obviously seen in H-plane direction (at ϕ =50º), whereby the main lobe of the copolarization is directed to 12 different angles at different switching states at frequency 2.4 GHz, as depicted in Figure Therefore, the radiation patterns discussed hereafter in this section are focused on the results in the H-plane direction due to the fact that the main lobe direction of the reconfigurable plasma antenna array seems to have no significant difference in term of angle in E-plane direction regardless of different switching states. Thus, the E-plane patterns are omitted because they are always directed towards 53. The resulting simulated radiation patterns offered by reconfigurable plasma antenna array demonstrating the beam steering capability in H-plane directions as presented in Figure (a) (b) (c) (d) 147

170 (e) (f) (g) (h) (i) (j) 148

171 (k) (l) Figure 6.25: Simulated results of radiation pattern for reconfigurable plasma antenna array at different switch configuration modes. The resulting set of radiation patterns demonstrating the beam steering capability in the H-plane as shown in Figure The beam can be directed at desired direction by switching ON the appropriate numbers of adjacent elements as discussed in section 6.4. The simulated HPBW is ±64. Moreover, Figure 6.26 presents the results from simulation and shows that the main beam directions can be pointed in the following directions depending on the switch configuration mode: 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330 and 360. These results clearly show that the main beam for the antenna can be steered by changing the switch configuration. 149

172 Figure 6.26 : Combination of simulated scanning radiation patterns in the H-plane for reconfigurable plasma antenna array. Figure 6.27 exhibits the simulated peak gains (abs) of reconfigurable plasma antenna array at the operating frequency of 2.4 GHz in Cartesian plots. The plots clearly illustrate that the reconfigurable plasma antenna array has similar peak gains at different angles regardless of different switching patterns. Figure 6.27 : Simulated peak gains (abs) of reconfigurable plasma antenna array with different main lobe directions at frequency 2.4 GHz. 150

173 Other simulated radiation characteristics of reconfigurable plasma antenna array are tabulated in Table 6.5. Table 5.5: Simulated radiation characteristics of reconfigurable plasma antenna array Number of sequence Gain (db) Directivity (dbi) HPBW ( ) Side lobe level (db) Main direction ( ) / lobe (a) (b) Figure 6.28: Reflection coefficient, S 11 (a) Measurement (b) Simulation. 151

174 Apart from that, to show the flexibility of the antenna design, the impedance of the antenna has been measured. The impedance of each of the reconfigurable plasma antenna array elements was measured based on the number of sequence as shows in Table 6.5. Meanwhile, Figure 6.28 shows the comparison between simulation and measurement results of S 11 when the reconfigurable plasma antenna array is operating at 12 different numbers of sequences at frequency 2.4 GHz. The measured impedance data were plotted for each number of sequences as shown in Figure 6.28 (a). It can be seen that very good agreement was obtained for all number of sequence, with the measured return loss lower than -10 db. The results from the simulation seemed to agree well with the measurement results. Hence, it had been proven that the reconfigurable plasma antenna array can be operated at a frequency of 2.4 GHz. As described previously, the design of reconfigurable plasma antenna array focused on the radiation pattern reconfiguration at a frequency of 2.4 GHz. In other words, the reconfigurable plasma antenna array had been expected to have pattern reconfigurabilities. Hence, the measurement for radiation patterns of reconfigurable plasma antenna array was conducted in an indoor anechoic chamber. The details of the measurement setup have been explained in the previous chapter. (a) (b) 152

175 (c) (d) (e) (f) (g) (h) 153

176 (i) (j) (k) (l) Figure 6.29: Simulated and measured radiation pattern in H-plane at frequency 2.4 GHz. Figure 6.29 exhibits the simulated and the measured radiation pattern in polar plot at frequency 2.4 GHz. The results clearly show that the reconfigurable plasma antenna array could be pointed with twelve different steerable beam directions at each frequency mode, 2.4 GHz (0,30,60,90,120,150,180,210,240,270,300, and 330 ). The results from the simulation seem to agree well with the measurement results. 6.6 SUMMARY In this chapter, the innovative design of reconfigurable antennas had been described. The design of antenna emphasized on using plasma elements as the reflector elements instead of using metal elements. The plasma antenna of beam- 154

177 switching was investigated based upon the interaction of plasma elements due to the incident of electromagnetic wave. Moreover, the simulated and the measured data were demonstrated for the concept of a reconfigurable plasma antenna array that could produce steering beam pattern characteristics, as presented in this chapter. This chapter also includes a comparative analysis on the effects of several antenna parameters. On top of that, good agreement was also achieved between simulation and measurement results. The results confirmed that the antennas could be steered in twelve directions, 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, and 330, respectively at frequencies across the entire 2.4 GHz band, with excellent transmission matching for all configuration modes. 155

178 CHAPTER SEVEN CONCLUSION, FUTURE WORKS AND RESEARCH CONTRIBUTION 7.1 CONCLUSION This thesis described the design that focused on the theory and the design using plasma element as a conductor element in antenna application. Three new antenna designs presented were the cylindrical monopole plasma antenna, monopole plasma antenna using fluorescent tube, and reconfigurable plasma antenna array. This project involved antenna design simulation, fabrication, and measurement processes in order to develop a new antenna design based on plasma medium instead of metallic medium. Furthermore, Computer Simulation Technology (CST) Studio Suite software packages have been employed to obtain the characteristics of the respective designed antennas. In the beginning of this thesis, a brief review of plasma has been discussed and explained. Next, in chapter 2 provides a review of previous work and information related to plasma antenna. Besides, explanation about theoretical equation plasma parameters was presented in chapter 3. Also included in this chapter is estimation of plasma frequency and collision frequency. Hence, it is necessary to estimate the value of these two parameters. Thus, several experiments were conducted to obtain approximations for plasma frequency and collision frequency. Meanwhile, chapter 4 depicts the investigation and analyses of the interaction between plasma behaviors to RF signal. The cylindrical monopole plasma antenna with three different types of gases; argon gas, neon gas and Hg-Ar gas were simulated and measured. The performances of cylindrical monopole plasma antenna had been validated and it was proven that plasma parameters did influence the performances of the antenna. Therefore, when the pressure was increased with the same type of gas, the collision frequency and the electron density also increased. When collision frequency was higher, the conductivity became lower, and thus, the gain decreased. In addition, the value of antenna gains also affected by size and mass of atom. When the 156

179 size and mass of atom is increase, the gain will be decrease. The measured radiation patterns were in good agreement with the simulation ones. On top of that, in chapter 5, by using commercial fluorescent tube, a monopole plasma antenna was fabricated and measured at 2.4 GHz. Based on the measurement results, it can be concluded that the commercial fluorescent tube with a coupling technique could be used to radiate radio signals. The radiation pattern of monopole plasma antenna measured at frequency 2.4 GHz showed that the pattern had been quite similar to the radiation pattern for classic monopole antenna. Thus, the findings of this study indicated that the plasma antenna could be considered as a monopole antenna. Besides, the results from the measurements for each structure seemed to agree well with the simulation results. In Chapter 6, the development of a new structure of pattern reconfigurable antennas was described and investigated, namely reconfigurable plasma antenna array. A reconfigurable plasma antenna array was developed with commercial fluorescent tube as a plasma element and it functioned as a reflector medium when plasma frequency was greater than the operating frequency. The significant function of the antenna was to produce twelve different beam-steering angles at frequency 2.4 GHz. This means, the main lobe of the radiation pattern of reconfigurable plasma antenna array can be directed to 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, and 330, with twelve direction and respectively at frequencies across the entire 2.4 GHz band, with excellent transmission matching for all the configuration modes. Moreover, the simulated and the measured data were demonstrated for the concept of a reconfigurable plasma antenna array that could produce steering beam pattern characteristics, as presented in this chapter. This chapter also includes a comparative analysis on the effects of several antenna parameters. Overall, the proposed antenna designs have achieved the objectives of this thesis. The problems highlighted at the beginning of this thesis have been successfully solved. In the following section, some possible improvement to the work performed in this research and possible avenues for further studies are presented. 157

180 7.2 FUTURE WORKS Based on the works done on plasma antenna in this research, the following are some other prospective studies that can be carried out in future research Different types of gases This research only focused on three types of gases; Argon, Neon, and Hg-Ar. The reason for only three gases introduced in this research had been because of the limitation in material. Thus, by having different types of gases, such Helium and Nitrogen with a variety of different pressures, many plasma parameters can be analyzed Operating Frequency In Chapter 5, the monopole plasma antenna using fluorescent tube was proven to work at a frequency of 2.4 GHz. Hence, this antenna can also be designed and fabricated to operate at other frequencies, such as at 5.8 GHz for WiMAX application. A new plasma model has to be developed in order to accommodate the loss sensitivity in plasma Different shape of plasma antenna In this thesis, the fluorescent tube that was used had been in cylindrical shape. The monopole plasma antenna and reconfigurable plasma antenna array can also be designed by using different shapes of fluorescent lamp, such as U shape and circle shape. 7.3 RESEARCH CONTRIBUTION Three contributions that are significant to plasma antenna technology have been identified in this research. Those are: 158

181 1. Identification of relationship between plasma parameter and microwave characteristic which can serve as guideline in future plasma antenna research. 2. Invention of new device with multi-function; lighting emitting device with antenna functioned. 3. Designing a reconfigurable antenna that use plasma element as a reflector antenna whilst other conventional reconfigurable antenna use metal element. 159

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193 APPENDICES 171

194 APPENDIX A Measurement of Positive Column, PC 172

195 APPENDIX B Data Sheet (Philips Fluorescent Lamp) 173

196 APPENDIX C Data Sheet Electronic Ballast 174

197 APPENDIX D Delta T 175

198 APPENDIX E Temperature Vs Vapor Pressure 176

199 APPENDIX F Periodic Table 177

200 APPENDIX G SMA Connector 178

201 APPENDIX H DC Block 179

202 APPENDIX I Aluminium Tape Datasheet 180

203 APPENDIX J Circuit Diagram For Transmitter 181