Theory and numerically computed results are presented for mutual coupling between two rectangular microstrip antenna patches.

-plane alignment and

-plane alignment are the two patch orientations considered. The

-parameter matrix element

is used to study the mutual coupling. Extensive results are provided for

covering several relative substrate dielectric constants, antenna patch widths, and antenna patch separations. Results are also given for resonant frequency, resonant impedance behavior, and radiation pattern at resonance.