Monopole Plannar Antenna Using Switchable Slot Structures Manoj K C Assistant Professor Department of ECE Vimal Jyothi Engineering College, Chemperi, Kannur, Kerala, India Stephy John PG Scholar Department of ECE Vimal Jyothi Engineering College, Chemperi, Kannur, Kerala, India Shayini R Assistant Professor Department of ECE College of Engineering Thalassery, Kannur, Kerala,India Abstract-In this letter, a novel compact frequency-reconfigurable monopole antenna with switchable states including narrowband states, and a dual-band state is presented. Two slot structures are used for finding the configurability of the antenna is achieved by using a switchable slotted structure on the ground plane. The designed antenna has a simplestructure and compact size of 40X40 mm. The antenna, which supports most applicable frequency bands above 2, can be used in multiradio wireless systems. Moreover, the proposed antenna, which has a combined UWB and narrowband functionality, has a good potential for use in cognitive radio. Keywords: Antenna, p-i-n diode, reconfigurable, switchable filter,cognitive radio(cr),ultra-wide band(uwb) I. INTRODUCTION Antennas enable wireless communications between two or more stations by directing signals toward the stations. The IEEE Standard Definitions of Terms for Antennas (IEEE Std145 1983) defines the antenna or aerial as a means for radiating or receiving radio waves. For wireless communication system, antenna is one of the most critical components. A good design of the antenna can relax system requirements and improve overall system performance. Microstrip patch antennas are widely implemented in many applications, especially in wireless communication. This is due to attractive features such as low profile, light weight, conformal shaping, low cost, high 251 efficiency, simplicity of manufacture and easy integration to circuits. However the major disadvantage of the micro strip patch antenna is its inherently narrow impedance bandwidth. Due to the rapid development of electronics and wireless communications, the demand for mobile devices operating at different standards or for different applications is extending. On the other hand, wireless systems are evolving toward multi-functionality. A reconfigurable antenna that has tuneable fundamental characteristics, including operating frequency, impedance bandwidth, radiation pattern, and polarization, is a well-suited candidate for providing multifunctionality [1]. Moreover, cognitive radio (CR), which is considered as the future of communications, needs a sensing antenna with the capability to monitor the spectrum, and a communicating antenna that can be reconfigured to communicate over a chosen frequency band. This has led to an elevated interest in the development of frequency reconfigurable antennas to utilize the spectrum efficiently [2]. Most of frequency-reconfigurable antennas are antennas only capable of switching between different narrowband modes. In [3], a switchable quad-band antenna by using a micro electromechanical systems (MEMS) switch has been proposed. By controlling the states of switches, the patch antenna in [4] can operate in four different frequencies. Recently, a number of reconfigurable antennas have been presented that combine wideband and narrowband functionality. In [6], a Vivaldi antenna that
shows band switching between a wideband mode and three narrowband modes has been proposed, by using four photoconductive switches, Configuration of the UWB monopole antenna. Reconfigurable antenna that has a dual band mode and narrowband modes has been designed. In [9], two reconfigurable monopole antennas with combined wideband and narrowband functionality have been proposed the first antenna by employing p-i-n diode switches, and the other using varactor diodes. In this letter, we propose a frequencyreconfigurable antenna with the capability to switch between narrowband, and dual band modes. The proposed antenna different switchable states: 4.78-5.45 (5.1), 2.91-4.8(3.1), 2.72-5.7 (4.95),8.02-8.7 (8.5) in switchable structure I and 2.99-4.05 8.02-8.7,10.5-11.45 3.45-3.99 in switchable structure II. The antenna, which uses a switchable slotted structure for reconfigurability, has a simple structure and smallest size. Details of the proposed design are described.. II.ULTRAWIDEBAND ANTENNA DESIGN A. Introduction Due to the rapid development of electronics and wireless communications, the demand for mobile devices operating at different standards or for different applications is extending. On the other hand, wireless systems are evolving toward multifunctionality. A reconfigurable antenna that has tuneable fundamental characteristics, including operating frequency, impedance bandwidth, radiation pattern, and polarization, is a well-suited candidate for providing multifunctionality. The antenna system for a cognitive radio is an integral part for its implementation. Two antennas are required for a CR system; first a wide band antenna which is usually a UWB antenna and the other is narrow band antennas which have 252 the frequency reconfiguration property. A UWB antenna is used to sense the spectrum in the range of 3.1 to 10.6 in order to find a vacant slot. The moment a vacant slot is obtained, the secondary user uses the narrow band antenna for transmitting data through that vacant slot. If the primary user needs that slot back for its use, then the frequency reconfiguration property which is integrated with the narrow band antenna helps to continue the data transmission through another vacant slot in the specified spectrum. B.UWB Antenna Design Here a circular monopole antenna has been chosen as a basic structure due to the fact that it can operate over wide bandwidth and has good radiation characteristics. Fig. shows the configuration of the proposed UWB monopole antenna. The antenna is constructed on an FR4 substrate with the relative permittivity of 4.4 and thickness of 1.6 mm. The size of the substrate is 40X40 mm. The radiating element is a circular patch with radius of 10 mm, which is fed with a 50Ω microstrip feed line with the length of 20 mm and width of 2.86 mm. On the bottom of substrate, there is a ground plane with 19X40 mm dimensions below the microstrip feed line. Designing of circular monopole antenna can be done using the transmission line equations. In typical design procedure, The essential parameters are Fig.1 configuration of the proposed UWB monopole antenna. Frequency of operation(fr):the resonant frequency of antenna must selected
appropriately. Resonant frequency selected for design is 3.1 Ghz Dielectric constant of the substrate (ɛr): Dielectric constant of the substrate plays an important role in antenna design. A substrate with high dielectric constant reduces the dimensions of the antenna but also affect the performance. So, there is a trade of between size and performance of patch antenna Height of the substrate (h): For the microstrip antenna to be used in communication systems, It is essential that the antenna not bulky. Hence the height of the dielectric should be less. C.Design of Circular Patch Circular Patch Radius and Effective Radius: Since the dimension of the patch is treated a circular loop, actual radius of the patch is given by Above equation does not take into consideration the fringing effect. Since fringing makes the patch electrically larger, the effective radius of patch is used and is given by III.UWB CIRCULAR ANTENNA WITH SLOT STRUCTURES ON GROUND PLANE Designed the UWB antenna with slot structures on ground plane.also studied the variation of vertical arm length on bandwidth. 253 Fig 3.1.structure I and II Length and width of the main slots are in structure I is 25mm and 1mm and vertical arms have length and width of 1.2mm and 3.5mm. Length and width of the main slots are in structure II is 35mm and 1mm and vertical arms have length and width of 1.2mm and 3.5mm. IV.SOFTWARE SIMULATION In this work, a circular UWB antenna has designed and simulated, also slots are included in the ground plane. microstrip The software used to model and simulate the proposed antenna was Ansoft HFSS, which is an industry-standard simulation tool for 3D fullwave electromagnetic field simulation. Here we designed and simulated ultra wide band antenna and also included slots on the ground plane. The designed UWB antenna now operates at two different narrowband frequencies (5.15-5.9 and 3.32-3.7 ). First we designed bandwidth of 3.1-10 having circular patch antenna on a FR4 substrate with dimensions of 40*40mm.
A.Results The proposed antenna has been simulated using Ansoft HFSS. The UWB antenna can be tuned to operate within the frequency range 3.1 10. Initially the location of the microstrip feed from the edge of the substrate is varied so as to achieve perfect impedance matching. Minimum -43 db return loss is available at resonant frequency which is at 3.1. Fig 4.1. Return loss curve Fig4.4 Return loss curve of structure II in HFSS V.NARROW-BAND ANTENNA DESIGN The UWB monopole antenna can be reconfigured by using a slotted structure placed on the ground plane. This structure, which acts as a filter, is designed to suppress frequencies outside the desired frequency band. On the other hand, the embedded slot below feed line causes stop bands in the UWB range and leaves a pass band between them [9]. The created pass band can be controlled by changing the length and shape of main slot. Below figure the input reflection coefficient of the antenna for different filter structures, by increasing the length of the main slot, the pass band of the antenna shifts down Structure 1 with Diodes Fig 4.2. Radiation pattern Fig4.3. Return loss curve of structure I in HFSS Fig. 5.1. Switchable filter structure I on the ground plane (unit: millimeters) A UWB to narrowband and dual-band modes reconfigurable antenna is introduced here by using the filter structure I &II and inserting a set of p-i-n diode switches inside these two structures.simulated reflection coefficient of the antenna for different filter structuresin Fig. 3.1.Fig. 4.3&4.4. Simulated reflection coefficient of the antenna for various values of 254
in Structure I&II Fig. 5.1 & 5.3. Switchable filter structure on the ground plane (unit: millimeters). The positions of the switches D1 and D2 are determined in creating desired frequency bands. For applying the dc voltage to p-i-n diodes, metal strips with dimensions of 2 0.6 mm were used inside the main slot. Moreover, for each p-i-n diode, a 100-pF dc blocking capacitor was placed in the slot to create the RF connection of the p-i-n diode and also to isolate the RF signal from the dc. In the introduced design, HPND-4005 beam lead p-i-n diodes [11] with extremely low capacitance were used. For biasing p-i-n diodes, a 0.7-V supply is applied to metal strips. The p-i-n diodes exhibit an ohmic resistance of 4.6 and capacitance of 0.017 pf in the ON and OFF states, respectively. By turning diodes on, the metal strips are connected to the ground plane and become a part of it. The desired frequency band can be selected by varying the states of p-i-n diodes, which changes the total equivalent length of the slot. TABLE I DETAILS OF P-I-N DIODE COMBINATIONS AND SIMULATED FREQUENCY BANDS IN EACH STATE FOR STRUCTURE I Diodes D1 D2 Frequency Band(simulated) State 1 ON ON 2.91-4.8 &8-9 (3.1) State 2 OFF OFF 4.78-5.45 (5.1) State 3 ON OFF 2.72-5.7(4.95 ) State 4 OFF ON 8.02-8.7 (8.5) According to the technical data sheet of thehpnd-4005, p-i-n diodes are simulated as a 4.6- resistor and 0.017-pF capacitor in the ON and OFF states Fig 5.2 &5.4.shows the simulated results of the input reflection coefficient for different states of the p-i-n diodes in slot structure I&II respectively. As it is seen from this figure, a good agreement exists between these results. For the proposed design, different operating states were investigated, and their corresponding diode states are shown in Table I&II. By turning all diodes, Whendiode D2 is off, depending on other diodes biasing condition, narrowband and dual-band modes are achievable. As an example from Table I, we can see when diodes D1 and D2 are off, the antenna s operating frequency Band is 2.91-4.8 (3.1).Meanwhile, in state 2 in which all diodes are off, the antenna will operate in its 4.78-5.45(5.1)frequency bands. Therefore, we can conclude that the frequency band is controllable by electronically changing the condition of p-i-n diode switches placed on the ground plane. The frequency bandwidth obtained by switching between different states can serve several wireless communications systems, including the WiMAX (2.3 2.4, 2.5 2.7, 3.3 3.8; 5.15 5.85 ), WiFi (2.4 2.48, 5.15 5.85 ), and UWB (3.1 10.6 ). From the results, good impedance matchingwith less than 10 db return loss is observed at all operating bands. 255
Fig.5.2. Simulated reflection coefficient of the antenna for different switching states in structure I Fig. 5.3. Switchable filter structure II on the ground plane (unit: millimeters) TABLE II DETAILS OF P-I-N DIODE COMBINATIONS AND SIMULATED FREQUENCY BANDS IN EACH STATE FOR STRUCTURE II Diodes D1 D2 Frequency Band (simulated) State 1 ON ON 2.99-4.05 State 2 OFF OFF 8.02-8.7 State 3 ON OFF 10.5-11.45 State 4 OFF ON 3.45-3.99 Fig. 5.4. Simulated reflection coefficient of the antenna for different switching states in structure II VI. CONCLUSION In this section of my work, a circular UWB antenna has designed and simulated. Then included slots structure I and II on the ground plane. When we include the slot structure I.Then it is obtained a result at 5.2 at -40 db.that is frequency of operation of the antenna is changed. When slot structure II is constructed on the ground plane.then obtained 256
a result at 3.7 at -24 db.again is operating frequency is changed to another one. The designed UWB antenna now operates at two different narrowband frequencies(5.2 and 3.7 ) with the inclusion of the slot structure I and II. Thus we can conclude that with the inclusion of different slot structures the frequency of operation of basic antenna changes.in next section The frequencyreconfigurable capability of the antenna is achieved by placing switches on the slot structure I&II in the ground plane. Also we can adjust the condition of switches.thiswill make the antenna reconfigurable. VI. REFERENCES [1] S. Yang, C. Zhang, H. K. Pan, A. E. Fathy, and V. K. Nair, Frequencyreconfigurableantennas for multiradio wireless platforms, IEEE Microw.Mag., vol. 10, no. 1, pp. 66 83, Feb. 2009. [2] FCC Spectrum Policy Task Force, Washington, DC, Report of the Spectrum Efficiency Working Group, Tech. Rep., 2002. [3] T. Wu,R.L.Li, S. Y. Eom, S. S.Myoung, K. Lim, J. Laskar, S. I. Jeon, and M. M. Tentzeris, Switchable quad-band antennas for cognitive radio base station applications, IEEE Trans. Antennas Propag., vol. 58, no. 5, pp. 1468 1476, May 2010. [4] A. F. Sheta and S. F. Mahmoud, A widely tunable compact patch antenna, IEEE Antennas Wireless Propag.Lett., vol. 7, pp. 40 42, 2008. [5] T. Y. Han and C. T. Huang, Reconfigurable monopolar patch antenna, Electron. Lett., vol. 46, no. 3, pp. 199 200, Feb. 2010. [6] M. R. Hamid, P. Gardner, P. S. Hall, and F. Ghanem, Switched-band Vivaldi antenna, IEEE Trans. Antennas Propag., vol. 59, no. 5, pp.1472 1480, May 2011. [7] G. P. Jin, D. L. Zhang, and R. L. Li, Optically controlled reconfigurable antenna for cognitive radio applications, Electron. Lett., vol. 47, no. 17, pp. 948 950, Aug. 2011. [8] M. R. Hamid, P. Gardner, P. S. Hall, and F. Ghanem, Vivaldi antenna with integrated switchable band pass resonator, IEEE Trans. AntennasPropag., vol. 59, no. 11, pp. 4008 4015, Nov. 2011. [9] A. Tariq and H. Ghafouri-Shiraz, Frequency reconfigurable monopole antennas, IEEE Trans. Antennas Propag., vol. 60, no. 1, pp. 44 50, Jan. 2012. [10] J. R. Kelly, P. S. Hall, and P. Gardner, Integrated wide-narrow band antenna for switched operation, in Proc. IEEE EuCAP, Berlin, Germany, 2009, pp. 3757 3760. [11] Avago Technologies, San Jose, CA, HPND-4005 beam lead PIN diode, Data sheet, 2006 [Online]. Available: http://www.avagotech.com/docs/av01-0593en [12] Ansoft High Frequency Structure Simulator (HFSS). ver. 11, AnsoftCorp., Framingham, MA, 2006 257