Effect of a finite ground plane on circularly polarized microstrip antennas

In this paper, the geometrical theory of diffraction (GTD) (R.G. Kouyoumjian and P.H. Pathak, Proc.IEEE, vol. 62, pp. 1448-1461, 1974) is employed to examine the finite ground plane effect for circularly polarized patch antennas. It is shown that a finite ground plane has a small effect on the radiation patterns of circularly polarized microstrip antennas in the forward direction. However, the effect on backside radiation and axial ratio in the forward radiation is noticeable when the four ground plane edges are asymmetric. This effect should be taken into consideration in designing circularly polarized microstrip antennas, and arrays, since their axial ratio bandwidth is generally very narrow.