Improved Expressions for Calculating the Impedance of Differential Feed Rectangular Microstrip Patch Antennas

This letter presents an analysis of the impedances of differential feed microstrip rectangular patch antennas. It is shown that the impedance of a differential feed antenna exhibits cosine squared behavior over the feed distance. We present improved expressions for calculating the impedance match feed positions of a differential feed rectangular microstrip patch antenna with given dimensions, on the base of which we designed two antenna prototypes. Both simulation and measurement results match our theoretical prediction.