Excitation and coupling of microstrip patch antennas of circular geometry

Green's functions have been applied to calculate the coupling between multiple patch antennas of circular geometry. We consider M patches to be fed by N feeders. The patches are not necessarily of the same size and the feeders can be either coax lines or microstrips. The interaction between patches has shown long range dependence on the patch separation, indicating that the coupling between patches is due to exchange of surface waves. The resonant frequency and input impedance have been calculated for an isolated antenna and for two coupled identical patch antennas. Our calculation compares very well with experiments.