A Comprehensive Study of Antenna Terminology Using HFSS

Transcription

1 IJECT Vo l. 5, Is s u e Sp l-1, Ja n - Ma r c h 2014 ISSN : (Online) ISSN : (Print) A Comprehensive Study of Antenna Terminology Using HFSS 1 Vasishath Kaushal, 1 Tanvir Singh, 1 Vinay Kumar, 2,3 Amit Kumar, 1 Dr. Dilip Kumar 1 Centre for Development of Advanced Computing, Mohali 2 JNV Theog, Shimla, HP, India 3 College of Information Science and Technology, Nanjing Forestry University, Nanjing, China Abstract Antenna is very important component of communication systems. By definition, an antenna is a device used to transform an RF signal, traveling on a conductor, into an electromagnetic wave in free space. Antennas demonstrate a property known as reciprocity, which means that an antenna will maintain the same characteristics regardless if it is transmitting or receiving. Antennas need to be optimized for specific applications like mobile phone, AM/FM, TV etc. And for that purpose the various properties like Size, Gain, Directivity, etc. are modified to get the best results. So, in this paper, we had presented a comprehensive study of antenna terminology by taking an example in HFSS (High Frequency Structured Simulator). Keywords Antenna, Directivity, Gain, HFSS, Radiation Pattern, SAR. I. Introduction When a signal is fed into an antenna, the antenna will emit radiation distributed in space in a certain way.most antennas are resonant devices, which operate efficiently over a relatively narrow frequency band. An antenna must be tuned to the same frequency band of the radio system to which it is connected, otherwise the reception and the transmission will be impaired. Fig. 1 shows antenna principle. A graphical representation of the relative distribution of the radiated power in space is called a radiation pattern. In this paper, antenna terminology is explained using HFSS Antenna Design kit which is shown in fig. 2. Fig. 2: Antenna Types in HFSS Simulator II. Antenna Simulators There are various antenna simulators available in the market for the purpose of simulating the behavior based on the specifications. These can be broadly classified into two categories, namely FDTD (Finite difference time domain) and FEM (Finite element method). A. FDTD The FDTD method is a numerical analysis technique used for modeling computational electrodynamics. Since it is a time domain method, it can cover a wide range of frequencies [2]. B. FEM Fem method is a numerical technique for finding approximate solutions to boundary value problems for differential equations. The various big names in this field are CST Studio, FEKO, Antenna Magus, and HFSS. Here, we have chosen(high Frequency Structured Simulator) HFSS, because the motive is to explain the basics of an antenna while keeping the complexity level at a minimum. HFSS uses the FEM solver technique [12-13]. III. Antenna Terminologies Fig. 1: Antenna Principle [1] A. Input Impedance For an efficient transfer of energy, the impedance of the radio, of the antenna and of the transmission cable connecting them must be the same [14]. Transceivers and their transmission lines are typically designed for 50 Ω impedance. If the antenna has an impedance different from 50 Ω, then there is a mismatch and an impedance matching circuit is required. Fig. 3 shows input impedance using HFSS. 24 International Journal of Electronics & Communication Technology

2 ISSN : (Online) ISSN : (Print) IJECT Vo l. 5, Is s u e Sp l-1, Ja n - Ma r c h 2014 the resonant half-wave dipole antenna. The method of measuring gain by comparing the antenna under test against a known standard antenna, which has a calibrated gain, is technically known as a gain transfer technique. Gain representation using HFSS is shown in fig. 6. Another method for measuring gain is the 3 antennas method, where the transmitted and received power at the antenna terminals is measured between three arbitrary antennas at a known fixed distance. Fig. 3: Input Impedance B. Return Loss The return loss is another way of expressing mismatch. It is a logarithmic ratio measured in db that compares the power reflected by the antenna to the power that is fed into the antenna from the transmission line. The representation of return loss is shown in fig. 4. Fig. 5: Directivity (Red Area Shows High Directivity) Fig. 4: Return Loss C. Bandwidth The bandwidth of an antenna refers to the range of frequencies over which the antenna can operate correctly. The antenna s bandwidth is the number of Hz for which the antenna will exhibit an SWR less than 2:1. The bandwidth can also be described in terms of percentage of the centre frequency of the band. Where FH is the highest frequency in the band, FL is the lowest frequency in the band, and FC is the centre frequency in the band. In this way, bandwidth is constant relative to frequency. If bandwidth was expressed in absolute units of frequency, it would be different depending upon the centre frequency. Different types of antennas have different bandwidth limitations. D. Directivity and Gain Directivity is the ability of an antenna to focus energy in a particular direction when transmitting, or to receive energy better from a particular direction when receiving [5, 8]. In a static situation, it is possible to use the antenna directivity to concentrate the radiation beam in the wanted direction. Fig. 5 shows directivity in which red area shows high directivity. However in a dynamic system where the transceiver is not fixed, the antenna should radiate equally in all directions, and this is known as an Omni-directional antenna. Gain is not a quantity which can be defined in terms of a physical quantity such as the Watt or the Ohm, but it is a dimensionless ratio. Gain is given in reference to a standard antenna. The two most common reference antennas are the isotropic antenna and Fig. 6: Gain E. Radiation Pattern The radiation or antenna pattern describes the relative strength of the radiated field in various directions from the antenna, at a constant distance and is shows in fig. 7. The radiation pattern is a reception pattern as well, since it also describes the receiving properties of the antenna. The radiation pattern is three-dimensional, but usually the measured radiation patterns are a two dimensional slice of the three-dimensional pattern, in the horizontal or vertical planes. These pattern measurements are presented in either a rectangular or a polar format [9-10]. Fig. 7: Radiation Pattern International Journal of Electronics & Communication Technology 25

3 IJECT Vo l. 5, Is s u e Sp l-1, Ja n - Ma r c h 2014 ISSN : (Online) ISSN : (Print) F. Beamwidth An antenna s Beamwidth is usually understood to mean the halfpower Beamwidth. The peak radiation intensity is found and then the points on either side of the peak which represent half the power of the peak intensity are located. The angular distance between the half power points is defined as the Beamwidth. Half the power expressed in decibels is 3dB, so the half power Beamwidth is sometimes referred to as the 3dB Beamwidth. Both horizontal and vertical beam widths are usually considered.assuming that most of the radiated power is not divided into side lobes, then the directive gain is inversely proportional to the Beamwidth: as the Beamwidth decreases, the directive gain increases. G. Sidelobes No antenna is able to radiate all the energy in one preferred direction. Some is inevitably radiated in other directions. The peaks are referred to as sidelobes, commonly specified in db down from the main lobe. H. Front-to-back Ratio It is useful to know the front-to-back ratio that is the ratio of the maximum directivity of an antenna to its directivity in the backward direction [7]. For example, when the principal plane pattern is plotted on a relative db scale, the front-to-back ratio is the difference in db between the level of the maximum radiation, and the level of radiation in a direction 180 degrees. Fig. 8 shows front to back ratio representation using HFSS. Fig. 8: Front to Back Ratio I. Reciprocity It is a fundamental property of antennas that the characteristics of an antenna described in the next section, such as gain, radiation pattern, impedance, bandwidth, resonant frequency and polarization, are the same whether the antenna is transmitting or receiving [11]. For example, the receiving pattern (sensitivity as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is driven and functions as a radiator. This is a consequence of the reciprocity theorem of electromagnetics. J. Resonant Frequency Many types of antenna are tuned to work at one particular frequency, and are effective only over a range of frequencies centered on this frequency, called the resonant frequency. These are called resonant antennas. The antenna acts as an electrical resonator. When driven at its resonant frequency, large standing waves of voltage and current are excited in the antenna elements. These large currents and voltages radiate intense electromagnetic 26 International Journal of Electronics & Communication Technology waves, so the power radiated by the antenna is maximum at the resonant frequency. K. Efficiency Efficiency is the ratio of power actually radiated to the power put into the antenna terminals. A dummy load may have an SWR of 1:1 but an efficiency of 0, as it absorbs all power and radiates heat but very little RF energy, showing that SWR alone is not an effective measure of an antenna s efficiency. Radiation in an antenna is caused by radiation resistance which can only be measured as part of total resistance including loss resistance. Loss resistance usually results in heat generation rather than radiation, and reduces efficiency. Mathematically, efficiency is calculated as radiation resistance divided by total resistance. L. Polarization It is important that other antennas in the same communication system be oriented in the same way, that is,have the same polarization. A horizontally polarized antenna will not usually communicate very effectivelywith a vertical whip. In the real environment, metal objects and the ground will cause reflections, and maycause both horizontal and vertical polarized signals to be present [3-4]. IV. Practical Observation Using HFSS Let us take an example. In this example a rectangular patch antenna (with probe feed) is designed and simulates using HFSS. Table 1 shows antenna dimensions and other parameters whereas fig. 9 shows the view of designed antenna in HFSS simulator. Fig. 10 to fig. 15 shows the different output parameters after simulating in HFSS. Table 1: Antenna Dimensions and Other Parameters Parameters Solution frequency (operating frequency) Patch length along X axis Patch width along Y axis Substrate thickness Substrate length along X axis Substrate width along Y axis Coax probe inner conductor radius Coax probe outer conductor radius Coax probe feed length Units 10 GHz 1.19 cm 0.91 cm 0.62 cm 2.7 cm 2.3 cm cm cm 0.5 cm Fig. 9: View of Designed Antenna in HFSS Simulator

4 ISSN : (Online) ISSN : (Print) IJECT Vo l. 5, Is s u e Sp l-1, Ja n - Ma r c h 2014 Fig. 10: Patch Radiation Pattern After Power Feeding Fig. 12: Input Impedance Chart (Smith Chart) Fig. 11: S11- parameter (Return Loss), Return Loss: db at 9.59 GHz Frequency Fig. 13: 3D Gain Plot Fig. 14: 2D Gain Report, [Antenna Gain:G= 5.61(Directivity of the Designed Antenna)] International Journal of Electronics & Communication Technology 27

5 IJECT Vo l. 5, Is s u e Sp l-1, Ja n - Ma r c h 2014 ISSN : (Online) ISSN : (Print) Fig.15: VSWR (Voltage Standing Wave Ratio) Report, [VSWR: 1.77 at 9.59 GHz Frequency] V. Conclusion The antennas are an integral and important part of a communication system. The different types of antennas with numerous parameters are used in different fields of applications. Research is going on to further optimize the parameters so as to obtain even better results. The simulation tools play a big role in such design procedures and researches. The aim is to maximize the radiation efficiency in the required direction while minimizing it in the back and side lobes. References [1] Antenna Basics, McGraw-Hill Higher Education, [Online] Available: free/ /62577/ch02_011_056.pdf [2] PA Tirkas, CA Balanis, Finite-difference time-domain method for antenna radiation, Antennas and Propagation, IEEE, [3] Kent Smith, Antennas for low power applications, [Online] Available: [4] Antenna Basics, Build your own Free-to-Air (FTA) Satellite TV System, [Online] Available: vendor-docs/motorola/ch4.pdf [5] Prasanna Ramachandran, T.S.Keshav, Laxmikant Minz Vamsikrishna Parupalli and ShaibalChakravarty, Antenna design, simulation and fabrication, , [Online] Available: [6] Ahmed A.Kishk, Fundamentals of antennas, [Online] Available: products/ / _chap01.pdf [7] Richard C. Johnson, Henry Jasik, Antenna Engineering Handbook, McGraw-Hill, 2nd Edition, [Online] Available: [8] CA Balanis, Antenna theory: Analysis and Design, John Wiley & Sons, [9] Davis, W. A. and Stutzman, W. L., Antenna Theory. Encyclopedia of RF and Microwave Engineering, Wiley Online Library, 2005 [10] Samuel Silver, Microwave antenna theory and design, Electromagnetic Wave Series, [11] Robert Elliot, Antenna theory and design, 2006, [Online] Available: Elliot-Antenna-Theory-and-Design-IEEE-Press 28 International Journal of Electronics & Communication Technology [12] I Bardi, Z Cendes, New directions in HFSS for designing microwave devices, Microwave Journal, [13] H Ansoft - Ansoft Corporation, Canonsburge, Version 13, PA, 2011 [14] John D. Kraus, Antennas, 2nd Edition, Tata McGraw Hill, Vasishath Kaushal is pursuing his Master s degree in Electronic Product Design from Centre for Development of Advanced Computing, Mohali, Punjab. He received his bachelor sdegree (Electronics and Communication engineering)from IET Bhaddal Technical Campus, Punjab. His area of interest includes Android, Linux and modern electronic product design. Tanvir Singh is pursuing his Master s degree in Embedded Systems from Centre for Development of Advanced Computing, Mohali, Punjab. He received his bachelor sdegree (Electronics and Communication engineering) from IET Bhaddal Technical Campus, Punjab. His area of interest includes Environmental Sustainability in Wireless Communication Networks, Electromagnetic Radiations with a dream tocreate a Technical Advanced and eco-friendly world. He has published 50+ review/research papers in International Journals/Conferences.

6 ISSN : (Online) ISSN : (Print) IJECT Vo l. 5, Is s u e Sp l-1, Ja n - Ma r c h 2014 Vinay Kumar is pursuing his Master s degree in Embedded Systems from Centre for Development of Advanced Computing, Mohali, Punjab. He received his bachelor sdegree (Electronics and Communication engineering)from Shobhit University. His area of interest includes Antenna Design. Amit Kumar received his bachelor s degree in Mathematics from the Himachal Pradesh University, Shimla, India, in 2002 and Masters degree in Computer Application from Kurukshetra University, Kurukshetra, India, in He completed his M.Phil. in Computer Science from Annamalai University, Annamalainagar, Tamilnadu, India, in He is currently pursuing his Ph.D. in Computer Science. He is working as a Faculty of Computer Science with NVS, MHRD, Department of Sec. & Hr. Education, Govt. of India and associated as a researcher with the Department of Computer Science, College of Information Science and Technology, Nanjing Forestry University, Nanjing, China. He has many publications in National /International Conference proceedings and International Journals. He is a reviewer for many international Journals. His research domain is Green Wireless Technologies and their Sustainable development. Dr. Dilip Kumar is a Senior Design Engineer at Centre for Development of Advanced Computing (C-DAC), Mohali. He has done his Ph.D in the area of Wireless Sensor Networks. He obtained his Master of Engineering (M.E.) from the Department of Electronics & Electrical Communication, PEC University of Technology, Chandigarh in 2003 and Bachelor of Engineering (B.E.) from the Department of Electronics & Telecommunication, Army Institute of Technology, University of Pune, Pune in He has published more than 50 high quality research papers in International journals and conferences viz. Elsevier, IEEE, ACM, Inderscience etc. International Journal of Electronics & Communication Technology 29