An Impedance Surface Technique for Wideband Matching and Miniaturization of Circular Patch Antennas

Abstract: In this work, we propose a technique to enhance the performance of circular patch antennas using an embedded system of cylindrical impedance surfaces. The technique utilizes a derived analytical model of a circular patch antenna containing an arbitrary number of coaxial impedance surfaces along with nonlinear optimization algorithms. This allows for the calculation of the radius and impedance of each surface to achieve the desired matching frequency band for given antenna dimensions. We demonstrate two applications of adding an optimal set of impedance surfaces into a compact circular patch antenna, i.e. the expansion of the matching frequency band keeping constant antenna dimensions, and the miniaturization (height reduction) maintaining the constant bandwidth. Two corresponding versions of a cavity-backed circular patch antenna each having three impedance surfaces are synthesized. Practical implementations for both versions are designed and considered in full-wave numerical verification of analytically predicted properties. A comparison with the conventional method using multi-element microstrip matching circuits shows a benefit in radiation efficiency.