An exact mutual coupling theory for microstrip patches

An accurate determination of mutual coupling between microstrip antennas is important in the design of finite arrays of patch elements. The classical formula for mutual impedance based on reciprocity is popular for determining such coupling. However, this formula ignores the presence of other open-circuited elements and consequently has serious limitations in accuracy due to resonant currents which may exist on such elements. In this presentation an exact theory for the mutual coupling between eatch elements will be presented, which circumvents this difficulty. For very weak coupling the exact formula reduces to the classical formula.