International Journal of Scientific and Research Publications, Volume 2, Issue 2, February 2012 1 Comparative Analysis of Microstrip Coaxial Fed, Inset Fed and Edge Fed Antenna Operating at Fixed Frequency B. Jyothi, B.T.P.Madhav, V.V.S. Murthy, P. Syam Sundar, VGKM Pisipati Department of ECE, K L University, Guntur DT, AP, India Abstract- There are so many techniques are available for feeding the microstrip patch antennas and each are having their own significance and impact on these antennas. The functional characteristics and output parameters of these microstrip antennas will be affected by choosing different feeding techniques. This paper deals with the comparative analysis of coaxial, inset and edge fed MSPA s with their simulated performance characteristics. All the three models are designed and simulated using Finite Element Method based antenna designing software Ansoft HFSS. substrate uses a thick low dielectric constant substrate, and the bottom substrate uses high dielectric substrate. The ground plane, which is in the middle, isolates the feed from radiation element and minimizes interference of spurious radiation for pattern formation and polarization. The main advantage of this method is allows independent of feed mechanism element [7-8]. Proximity coupling has the largest bandwidth, has low spurious radiation. Length of feeding stub and width-to-length ratio of patch is used to match Index Terms- coaxial feeding, inset feeding, edge feeding, FEM. M I. INTRODUCTION icrostrip patch Antennas has various advantages such as low profile, light weight, easy fabrication. Feed line is used for excite to radiate by direct or indirect contact. Microstrip patch antennas can be fed in a variety of ways.1.contacting 2.Non-Contacting. In contacting method the RF power is fed directly to the radiating patch using a connected element, they are microstrip feed and coaxial feed [1]. In Non Contacting method, electromagnetic coupling is done to transfer the power between the feed line and the radiating patch, they are Aperture coupled feed and Proximity coupled feed [2]. II. FEEDING TECHNIQUES Microstrip line feed is one of the easier methods to fabricate as it is a just conducting strip connecting to the patch and therefore can be consider as extension of patch. It is simple to model and easy to match by controlling the inset position. The disadvantage of this method is that as substrate thickness increases, surface wave and spurious feed radiation increases which limit the bandwidth [3-4]. In Coaxial feeding, the inner conductor of the coaxial is attached to the radiation patch of the antenna while the outer conductor is connected to the ground plane. The main advantages of this method are easy to fabricate, easy to match and low spurious radiation [5-6]. Aperture coupling consist of two different substrate separated by a ground plane. On the bottom side of lower substrate there is a microstrip feed line whose energy is coupled to the patch through a slot on the ground plane separating two substrates. Top Fig. 1 Coaxial Fed Rectangular Patch Antenna Fig. 2 Inset Fed Rectangular Patch Antenna
International Journal of Scientific and Research Publications, Volume 2, Issue 2, February 2012 2 Fig. 3 Edge Fed Rectangular Patch Antenna Figure (1) shows the coaxial fed Microstrip rectangular patch antenna designed to work at 5.2 GHz. Figure (2) shows the Inset fed microstrip rectangular patch antenna designed to work at 5.2 GHz. Figure (3) shows the Edge fed microstrip rectangular patch antenna designed to work at 5.2 GHz. III. RESULTS AND ANALYSIS Fig. 4 Return Loss Vs Frequency
International Journal of Scientific and Research Publications, Volume 2, Issue 2, February 2012 3 Fig. 5 2D Gain Return loss is the difference, in db, between the forward and reflected power measured at a given point in an RF system. A mismatched antenna reflects some of the incident power back toward the transmitter and since this reflected wave is traveling in the opposite direction as the incident wave, there will be some points along the cable where the two waves are in phase and other points where the waves are out of phase. The return loss obtained for three models is shown in figure (4). The return loss obtained for three models are -26.52, -12.02, -10.87 db respectively. The return loss is increasing when we select edge feeding and inset feeding compared with coaxial feeding. Fig. 6 Contour Plot for radiation pattern in Phi direction The gain of the antenna in given direction is the amount of energy radiated in that direction compared to the energy an isotropic antenna would radiate in the same direction when driven with the same input power. The direction in which the antenna is radiating its most of its power is called its gain. The gain obtained for three models are 7.93, 7.95 and 7.45 db respectively. The gain is marginally high for the inset feed antenna and slightly less for edge feed antenna. The radiation pattern of the antenna can be defined as the spatial distribution of a quantity that characterizes the electromagnetic field generated by an antenna. Figure (6) and (7) shows the radiation pattern contour plots of the antenna in phi and theta directions. The contour plots represent the radiation pattern in elevation and azimuthal angles. The radiation pattern represents the energy radiated from the antenna in each direction, often pictorially.
International Journal of Scientific and Research Publications, Volume 2, Issue 2, February 2012 4 Mesh generation is the practice of generating a polygonal or polyhedral mesh that approximates a geometric domain to the highest possible degree of accuracy. The term "grid generation" is often used interchangeably. Typical uses are for rendering to a computer screen or for physical simulation such as finite element analysis or computational fluid dynamics. Figure (8) shows the current distribution on the patch of the antenna for three models of feeding. Fig. 7 Contour Plot for radiation pattern in Theta direction Fig. 8 Current Distribution over the patch in three types of feeding
International Journal of Scientific and Research Publications, Volume 2, Issue 2, February 2012 5 Table (1) and (2) shows the antenna additional parameters and the maximum field data. Antenna Parameters Table 1: Antenna Parameters Quantity Probe-fed(Value/Units) Edge-fed(Value/Units) Inset-fed(Value/Units) Max U 0.0031973W/Sr 0.0032096W/Sr 0.004259W/Sr Peak Directivity 6.3038 5.7038 6.3612 Peak Gain 6.2126 5.5625 6.2422 Peak Realized Gain 4.0711 4.0334 5.3522 Radiated Power 0.0063739W 0.0070715W 0.0084138W Accepted Power 0.0064675W 0.0072511W 0.0085742W Incident Power 0.0098694W 0.01W 0.01W Radiation Efficiency 0.98553 0.97522 0.98129 Front to Back Ratio 144.83 83.426 386.19 Maximum Field Data re field Probe -fed (value/units) Probefed (at phi) Probefed (at theta) Table 2: Maximum Field Data Edge-fed (value/units) Edgefed (at phi) Edgefed (at theta) Insert-fed (value/units) Insertfed (at phi) Insert-fed (at theta) TOTAL 1.5527v 90deg -4deg 1.5557v 90deg 6deg 1.729v 90deg 6deg X 0.34194v 135deg 52deg 0.29898v 130deg 60deg 0.31079v 45deg 56deg Y 1.5506v 85deg -2deg 1.5518v 95deg 2deg 1.7863v 85deg 4deg Z 0.74523v 90deg -44deg 0.82391v 90deg 46deg 0.85778v 90deg 44deg PHI 1.5473v 180deg 0deg 1.5472v 180deg 0deg 1.7761v 180deg 0deg THETA 1.5527v 90deg -4deg 1.5556v 90deg 6deg 1.792v 90deg 6deg LHCP 1.1365v 10deg -10deg 1.1116v 125deg 16deg 1.2736v 125deg 8deg RHCP 1.131v 170deg -10deg 1.112v 55deg 16deg 1.277v 55deg 8deg IV. CONCLUSION Different types of feeding techniques are applied to rectangular patch antenna and its performance characteristics are observed at fixed frequency. Coaxial feeding is giving better return loss and inset feeding is giving superior gain compared to the other feeding techniques. Radiation efficiency is showing better result for coaxial feeding and radiated power is high for the case of edge feeding. The inset and edge feeding are easier in construction. Overall the coaxial feeding is giving better input impedance and other parameters compared to other different feeding techniques. The only problem is with the coaxial feeding is its design complexity. ACKNOWLEDGEMENT The authors like to express their thanks to the department of ECE and management of K L University for their continuous support and encouragement during this work. Further, VGKM Pisipati acknowledges the financial support of Department of Science and Technology through the grant No.SR/S2/CMP-0071/2008. REFERENCES [1] P.J.Soh, M.K.A.Rahim, A.Asrokin & M.Z.A.Abdul Aziz, Design, Modeling, and performance comparison of feeding techniques for a microstrip patch antenna. Journal Teknologi, 47 (D) Dis.2007: 103-120 universiti technologi Malaysia. [2] Kazuhiro Kitatani, Sadahiko Yamamoto. Coaxial feed-type microstrip patch antenna with variable antenna height. Electronics and Communications in Japan (Part I: Communications), Volume 87, Issue 2, pages 10 16, February 2004. [3] B.T.P.Madhav, K.Praveen Kumar, N.Srinivas Sri Chaitanya, P.Rakesh Kumar, N.V.K.Ramesh, B.Nagaraju Nayak, Comparative Analysis of Shorting Pin and Shorting Plate Models for Size Reduction in the Microstrip Patch Antennas, International Journal of Communication Engineering Applications-IJCEA,ISSN: 2230-8504; e-issn-2230-8512vol 02, Issue 04; July 2011 [4] K. F. Lee, K. M. Luk, K. F. Tong, S. M. Shum, T. Huynh, and R. Q. Lee, Experimental and simulation studies of the coaxially fed U-slot rectangular patch antenna, Inst. Elect. Eng. Microwave Antennas Propagation, vol. 144, no. 5, pp. 354 358, Oct. 1997. [5] Y. X. Guo, C. L. Mak, K. M. Luk, and K. F. Lee, Analysis and design of L-probe proximity fed-patch antennas, IEEE Trans. Antennas Propagat., vol. 49, pp. 145 149, Feb. 2001. [6] K. M. Luk, C. L. Mak, Y. L. Chow, and K. F. Lee, Broadband microstrip patch antenna, Electron. Lett., vol. 34, no. 15, pp. 1442 1443, 1998.
International Journal of Scientific and Research Publications, Volume 2, Issue 2, February 2012 6 [7] Zhang, Y.P. and J.J. Wang, 2006. Theory and analysis of differentiallydriven microstrip antennas. IEEE Transactions on Antennas and Propagation, 54(4): 1092-1099. [8] Mak, C.L. and K.M. Luk, 2000. Experimental study of a microstrip patch antenna with an L-shaped probe. IEEE Transactions on Antennas and Propagation, 48(5): 77-78. AUTHORS First Author B.T.P.Madhav was born in India, A.P, in 1981. He received the B.Sc, M.Sc, MBA, M.Tech degrees from Nagarjuna University, A.P, India in 2001, 2003, 2007, and 2009 respectively. From 2003-2007 he worked as lecturer and from 2007 to till date he is working as Assistant Professor in Electronics Engineering. He has published more than 70 papers in International and National journals. His research interests include antennas, liquid crystals applications and wireless communications. Second Author B.Jyothi, was born in A.P, India in 1981. She completed her B.Tech in 2003 from CR Reddy College of Engineering affiliated to Andhra University. Presently she is pursuing her M.Tech, in Communications and Radar Systems from K L University. Third Author Prof. VGKM Pisipati was born in India, A.P, in 1944. He received his B.Sc, M.Sc and Ph.D degrees from Andhra University. Since 1975 he has been with physics department at Acharya Nagarjuna University as Professor, Head, R&D Director. He guided 22 PhDs and more than 20 M.Phils. His area of research includes liquid crystals, nanotechnology and liquid crystals applications. He visited so many countries and he is having more than 260 International research publications. He served different positions as academician and successfully completed different projects sponsored by different government and non-government bodies. He is having 5 patents to his credit. Fourth Author V.V.S.Murthy was born on 02 January, 1981. He received his B.E. and M.Tech degrees in 2002 and 2006 respectively. He is a life member of IETE and ISTE. His research areas include Antennas and Radio wave propagation and optical image processing. Currently he is working as Associate Professor in ECE department of K.L.University, Guntur.