Comparison of Direct Contact Feeding Techniques for Rectangular Microstrip Patch Antenna for X-Band Applications R. Kiruthika II M.Tech.(ECE), Department of Electronics Engineering Pondicherry University, Pondicherry sakthiprime@gmail.com Dr. T. Shanmuganantham Assistant Professor, Department of Electronics Engineering Pondicherry University, Pondicherry shanmuga.dee@pondiuni.edu.in Abstract—A Microstrip Patch Antenna for radar application with direct contact feeding techniques is presented. In this paper, direct contact feeding methods like coaxial probe feed, line feed, inset feed and stepped-line inset feed are designed and analyzed. In contact feeding techniques, the RF power is directly applied to the radiating patch. The antenna is designed to resonate at X-band frequency. The X-band frequency range lies between 8 to 12 GHz and are used in radar applications. The substrate material used by the antenna is the low cost FR4 Epoxy. The Ansoft HFSS V.12 software is used to analyze the results of different feeding techniques. The parameters like return loss, bandwidth, gain and directivity are compared and discussed in this paper. Keywords-Microstrip Patch Antenna; direct contact feeding; return loss; bandwidth; gain; directivity I. INTRODUCTION Microstrip Patch Antennas has several advantages over other antennas due to their light weight, low profile, low cost of production, and are easily compatible with optoelectronic integrated circuits (OEICs) and microwave monolithic integrated circuits (MMICs). Due to these attractive features, the researchers are having significant attention towards microstrip antennas [1-3]. Microstrip antennas are used in wide variety of applications in wireless communication and biomedical diagnosis [4]. In recent years, the widespread proliferation of wireless communication has increased the demand for compact broadband antennas. But it has a disadvantage of producing low gain and narrow bandwidth. To overcome the inherent limitation, many techniques such as probe fed antenna, patch antenna with thick substrate electrically, stacked shorted patches and slotted patch antenna have been proposed and investigated [2]. In this paper, the rectangular microstrip patch antenna is designed and compared for various direct contact feeding techniques. The feeding method given for excitation can be of either direct contact or non-contact method. The direct contact method involves the RF power directly fed to the patch. In non-contact method, the RF power is not directly fed to the patch, instead transferred to the patch through electromagnetic coupling. For ease of analysis, the rectangular microstrip patch antenna with coaxial probe feed, line feed, inset feed and stepped-line inset feed is considered. Due to difficulty in fabrication, the non-contact feeding method is not considered here. The X-band frequency range proposed is of shorter wavelength and can be used for deep space telecommunication and military satellite application. This short wavelength characteristic provides an image with high resolution for identification and discrimination of targets [8]. II. FEEDING TECHNIQUES A brief description about the various direct contact feeding techniques are compared in this paper and is given as follows: A. Coaxial Probe feed The coaxial probe feed comprises of inner and outer conductor. It is the most widely used feeding technique due to the advantage that it can be placed anywhere along the radiating patch [5]. The outer conductor of the coaxial cable is attached to the ground plane, while the inner conductor extends through the dielectric substrate and is connected to the conducting metal patch. The parametric advantage of the coaxial fed antenna is that it provides high gain and good impedance matching with considerable bandwidth. Mismatch between the results of simulation and fabrication is the most common significant disadvantage of coaxial feeding technique. Generally, the mismatch error is due to the improper insertion of inner coax feed at the time of fabrication [6]. B. Microstrip line feed This feeding involves the conducting strip directly connected to the edge of the radiating patch [7]. This provides an advantage for arrangement of feed and patch on the same plane and can etched easily on the same substrate. The width of the feed is comparatively smaller than that of the patch. C. Inset feed It is similar to that of the microstrip line feed, with a modification that an inset cut is created along the patch, with a desired dimension. The main advantage of this inset cut feeding is to provide good impedance matching of the feed line to the patch, without any use of additional matching element. Here also the width of the feed is smaller compared to that of the radiating patch element. D. Stepped- line Inset feed The stepped feed line has the advantage of providing good radiation characteristics compared to that of ordinary line feeding techniques. The stepped line feed is applied by providing stepped cuts along either side of the line feed in a Vol. 14 CIC 2016 Special Issue International Journal of Computer Science and Information Security (IJCSIS) https://sites.google.com/site/ijcsis/ ISSN 1947-5500 International Conference on Advances in Computational Intelligence and Communication (CIC 2016) Pondicherry Engineering College, Puducherry, India October 19 & 20 - 2016 12