Design of a circular polarized nearly square microstrip patch antenna with offset feed

This paper presents the design of a circular polarized nearly square patch antenna using an offset microstrip feed. By using an offset feed instead of the normal corner feed, it is shown that the area of the perturbation segment must increase in order to maintain circular polarization. Consequently, the effect of manufacturing errors on the axial ratio is reduced. Using a fixed offset feed position, the dimensions of the antenna are uniquely obtained. The antenna is matched using a simple matching network consisting of a short length of microstrip line. A matched antenna was designed to operate at 2.45 GHz, and an axial ratio of <0.5 dB with a return loss of >20 dB was obtained experimentally. The predicted, simulated and practical results are shown to be in good agreement.