Broadband Semielliptical Patch Antenna with Semicircular Ring Slot for WiMax Application

This paper reports the design and analysis of a semielliptical patch antenna modified by cutting semicircular ring slot in patch geometry and obtained results are discussed. The reported antenna is designed on a multilayered substrate material having two glass epoxy FR-4 substrates separated by a thin foam substrate having thickness 1.0？mm. The size of ground plane is 75？m 5？mm, whereas the patch dimension along major and minor axes is 23.0？mm and 14.0？mm, respectively. The two modes corresponding to resonance frequencies 3.39？GHz and 3.73？GHz are excited to provide wide impedance bandwidth 21.1% with respect to central frequency with stable radiation patterns. The antenna shows circular polarization with axial ratio bandwidth 5.5% and minimum axial ratio value 1.65？dBi. The radiation patterns of proposed antenna are normal to the surface of patch and are almost identical in shape as required for practical applications. The proposed antenna covers entire median band of WiMax communication systems ranges from 3.40？GHz to 3.6？GHz. 1. Introduction Conventional microstrip antennas in general have a conducting regular shaped patch printed on a grounded microwave substrate and have the attractive features like low profile, light weight, easy fabrication, and low cost on mass production. However, microstrip antennas inherently have narrow bandwidth, low gain, and normally operate at a single frequency corresponding to their dominant mode [1, 2]. For practical applications of these antennas, bandwidth and gain enhancement are usually demanded. With increasing demand of antennas for modern wireless communication systems, compact broadband planar antennas covering a wide frequency range are desired. Among the conventional patch geometries, microstrip antennas with rectangular, circular, or triangular shapes are extensively analyzed [2]. However patch shapes like elliptical patch are rarely touched upon by researchers perhaps due to the involvement of difficult mathematical modeling and involved boundary conditions during their analysis. The main advantage of elliptical patch is that circular polarization may be achieved more easily than in rectangular or circular patches. Looking at this benefit, several workers have analyzed regular elliptical patches but their realized impedance bandwidth was narrow [3–5]. Microstrip patches were recently modified to improve their performance either by inserting appropriate slot [6–8] or by increasing substrate thickness [9] or by using low permittivity substrate material [10] or by parasitic patches [11]. The wireless