Design of Single Fed Aperture Coupled Microstrip Antennas for WLAN Rashid A. Saeed, S. Khatun, Borhanuddin, M. A. Khazani, Rania A. Mokhtar Computer and Communications System Engineering, Engineering Faculty, Universiti Putra Malaysia 43300, Kuala Lumpur, Malaysia Eng_rashidWieee.org Abstract- The advantages of microstrip antennas have made them a perfect candidate for use in the wireless local area net- work (WLAN) applications. This paper presents theoretical in- vestigation and simulation of Input Impedance behavior of nearly square single fed aperture coupled microstrip patch antenna that can satisfy the narrowband WLAN applications with 2.4 GHz band with 80 MHz bandwidth. For maximum coupling the patch should be centered over the slot, moving the patch relative to the slot in the H-plane direction has little effect, while moving the patch relative to the slot in the E-plane (resonant) direction will decrease the coupling level, also for maximum coupling, the feed line should be positioned at right angles to the center of the slot. Skewing the feed line from the slot will reduce the coupling, as will positioning the feed line towards the edge of the slot. Position of the feed line in different places relative to patch also was pre- sented. Keywords-Microstrip antenna, WLAN, input inqedance, polarization, feeding techniques. I. INTRODUCTION T naperture coupled patch antennas have found widespread applications in communication systems during the last decade. Their most important advantage that makes them preferable from microstrip line or probe fed patches is the ability to use separate substrates for the feeding network and the patch itself. In their usual structure a patch printed on a low dielectric constant substrate (e.g. foam) is excited by an aperture in the ground plane which is in tum excited by a microstrip line printed on a separate substrate covering the other side of the ground plane. This configuration reduces the surface wave effects on the patch antenna, it enhances its bandwidth, it is isolating the feeding lines spurious radiation and leaves more space for the feeding network. This latter advantage makes them very attractive for phased arrays applications where phase shifters and/or power dividers must be incorporated in the feeding network. Mathematical modeling of the basic microstrip radiator was initially carried out by the application of transmission-line analogies to simple rectangular patch fed at the center of radiating wall. The radiation pattem of a circular patch was Mahmoud Alshamary Electronics Department, Engineering Faculty, Sudan University of Science and Technology (SUST) 72, Eastern Diems, Khartoum, Sudan analyzed and measurements reported by Carver [1]. The mathematical analyze of a wide variety of microstrip patch shapes was discussed in [2]. Which used the modal-expansion technique to analyze to rectangular, circular, semicircular, and triangular patch shapes. High speed, broadband and high capacity in or indoor wireless local area networks (WLAN) are becoming more and more predominant today, its interesting to become familiar with some of the aspects of wireless design that must be faced and overcome. The advantages of microstrip antennas have made them a perfect candidate for use in the wireless local area network (WLAN) applications. Though bound by certain disadvantages, microstrip patch antennas can be tailored so they can be used in the new high-speed broadband WLAN systems and other applications, e.g. PCS, Bluetooth, RFID, etc. II. PREPARE FOUNDATION FOR MIcROSTmIP DESGIN A microstrip patch antenna is a radiating patch on one side of a dielectric substrate, which has a ground plane on the underside [3]. The EM waves fringe off the top patch into the substrate, reflecting off the ground plane and radiates out into the air. Radiation occurs mostly due to the fringing field between the patch and ground (shown in figure 1). The radiation efficiency of the patch antenna depends largely on the permittivity (£ ) of the dielectric. Ideally, a thick dielectric, low Cr and low insertion loss is preferred for broadband purposes and increased efficiency. The advantages of microstrip antenna that they are low-cost, confornable, lightweight and low profile, while both linear and circular polarization easily achieved. These attributes are desirable when considering antennas for WLAN systems. Disadvantages of microstrip antenna include such as a narrow bandwidth, a low gain (-6 dB) and polarization purity is hard to achieve [3]. A. Polarization Types Usually the polarization of the wave radiated by the antenna in a particular direction. This is usually dependant on the feeding 1-4244-0000-7/05/$20.00 ©2005 IEEE. 7