RESEARCH ARTICLE Inventi Rapid: antennas & propagation Vol. 2012, Issue 1 2012eap011, CCC: $10 © Inventi Journals (P) Ltd Published on Web 04/02/2012, www.inventi.in INTRODUCTION Microstrip patch antennas have been much attracted due to their lower profile, light weight, and easy fabrication so it can be used in the satellite and wireless mobile communication applications [1]. The geometries of patch antennas like rectangular, circular and triangular patch are the most extensively analyzed patch antenna geometries in recent years and now these geometries are modified as per the application to improve their performance [2]. Circular disk microstrip patch antenna is one of the simplest patch configurations. There are various models for analyzing the circular disk patches such as: cavity model, mode matching with edge admittance, transmission line model and Finite Difference Time Domain (FDTD) [1-4]. Circular patches were reported to lose less energy by radiation and thus provide larger quality factors than other configurations e.g. rectangular patches. The directivity of circular or disk patch antenna is more when compared with rectangular patch antenna. The patch structure can be modified to have application specific resonating frequency and to have higher gain and bandwidth response [5]. Among many existing techniques like cross slot embedded in the center, embedding a circular hole or using slits etc. here dual band is achieved by cross slot at center of circular patch. J.H Lu analyzed a circular patch antenna and its arrays with a pair of L-shaped slots for dual-frequency operation[6].Dual-frequency patch antennas provides an alternative to large-bandwidth planar antennas, in applications in which large bandwidth is needed for operating at two separate transmit receive bands. When the system operation requires two frequencies, dual- frequency patch antennas may be to avoid the use of two different antennas at two different frequencies [7]. Antenna Design The geometry of the proposed antenna is shown in Fig. 1 V.T. Patel Dept. of Electronics & Communication, Charotar University of Science & Technology, Changa, Gujarat,India. E-mail: ankit.ponkia@ymail.com *Corresponding author 2 Noble Group of Institution Junagadh, Gujarat Technological University, Ahmedabad, Gujarat, India. • The antenna parameters are also given in Figure 1. The antenna is mounted on an Roger RT/Duriod 5880(tm) substrate having reletive permittivity of 2.2 and dielectric loss tangent tan δ=0.009 The antenna is fed by a coaxial transmission line the method called probe feeding. The Simulation results of proposed antenna are performed by HFSS TM . HFSS stands for High Frequency Structure Simulator. HFSS is a high-performance full- wave electromagnetic (EM) field simulator for arbitrary 3D volumetric passive device modeling that takes advantage of the familiar Microsoft Windows graphical user interface (GUI).It integrates simulation, visualization, solid modeling, and automation in an easy-to-learn environment where solutions to your 3D EM problems are quickly and accurately obtained.Ansoft HFSS employs the Finite Element Method (FEM), adaptive meshing, and brilliant graphics to give you unparalleled performance and insight to all of your 3D EM problems. Ansoft HFSS can be used to calculate parameters such as S Parameters, Resonant Frequency, and Fields [8]. The antenna structure uses patch with radius of 22 mm and thickness of 0.5 mm,ground plane with thickness of 1 mm both made from copper plate with relative permittivity of 1.Feed with inner conductor radius of 0.12 mm is located at 12 mm. Excitation to patch conductor is given using waveport.Simulation were performed with proper feed location to obtain frequency reponse extending from 1 GHz to 5 GHz.It gives return loss (S11) which is further used to calculate VSWR (Voltage Standing Wave Ratio). Simulation Results The configuration as shown in Figure 1, the feed locations are optimized by keep on changing their locations to have dual frequency bands and two frequency bands of operation have been achieved. The simulation results are shown in the Figure 3 below containing return loss S11 (db) and VSWR. Table 1 shows analysis of simulation results for configuration of figure 1 by keeping feed location as variable. From table it can be observed that VSWR at every band is near to 1.Also return loss S11 is maximum. There are two bands at frequency of 2.4 GHz in ISM band and 4.2 GHz for C-band downlink application can be achieved. The figure 4 shows new configuration of antenna after changing dimension of cross slot in the circular patch and keeping all other parameters constant except substrate height. By tuning substrate height we can have dual band response. Table 2 shows analysis of simulation results for configuration of figure 4 by keeping substrate height as variable. Figure 5 shows Return loss S11 and VSWR plots.As shown dual band with frequency 2 GHz can be used used for 3G (UMTS- Universal Mobile Telecommunication System) uplink (1.885–2.025 GHz) application and 3.48 GHz for extended- C Band (Lower-3.4 to 3.7 GHz- downlink) applications.For antenna geometry of figure 5 radiation pattern and 3D plot for total gain are shown in figure 6. CONCLUSION From the simulation results we can see that by tuning the antenna parameters like feed location and substrate height, and slot length or width dual band frequency response can be achieved with wideband, providing good return loss and VSWR behavior. REFERENCES AND NOTES 1. R. Garg, P. Bhartia, I. J. Bahl and A. Ittipiboon,"Microstrip antenna design handbook", Artech House: New York, 2001. 2. J R James & P S Hall, “Handbook of Microstrip Antennas”, IEE Electromagnetic Waves Series 28, Peter Peregrinus Ltd., London. 3. Deschamps, G.A., “microstrip microwave antennas” 3rd USAF symposium on antennas, 1953. 4. C. A. Balanis, “Antenna Theory, Analysis and Design”, John Wiley & Sons, New York, 1997. 5. Binu Paul, S. Mridula, C. K. Aanandan, P. Mohanan, “A new microstrip patch antenna for Dual Band Circular Shaped Slotted Microstrip Patch Antenna Ankit V Ponkia 1* , Ved Vyas Dwivedi 2 , Jitendra P Chaudhari 1 Abstracts: In this paper software based design and analysis has been carried out for a slotted circular patch antenna for dual band applications. A circular patch (radius 22 mm and thickness 0.5 mm) with cross slot etched at center provides dual band operation. The design is analyzed by Finite Element Method based HFSS EM Simulator Software. The designed antenna operates on ISM (Industrial, Scientific and Medical) band, UMTS (3G) and C-Band. Key Words: Dual Band, Microstrip Antennas, Return Loss, VSWR. Table 1: Analysis by changing feed location Feed location (x,y) in mm Band 1 Band 2 Frequency (GHz) S11 dB VSWR Frequency (GHz) S11 dB VSWR (12,-12) 2.4 -34.52 1.03 4.16 -14.90 1.12 (12,-15) 2.4 -27.22 1.03 4.20 -19.25 1.34 (15,-15) 2.42 -24.30 1.19 4.16 -24.31 1.12 Table 2: Analysis by changing substrate height Substrate height in mm Band 1 Band 2 Frequency (GHz) S11 dB VSWR Frequency (GHz) S11 dB VSWR 5 2.00 -32.81 1.04 3.48 -12.46 1.62