A Rigorous Approach to Mutual Coupling in General Antenna Systems Through Perturbation Theory

We provide a theory for describing and computing mutual coupling in arbitrary antenna arrays by applying a perturbation approach to the antenna current Green´s function of the problem. In particular, there is no need to invert the full electromagnetic operator of the problem. The procedure proposed in this letter consists of showing that mutual coupling can be estimated by: 1) measurement or computation of the individual device performance; 2) approximation of forward interactions between the elements; and 3) computing the coupling effects algebraically by a perturbation series. The technique is fully general and applies to antennas with arbitrary shape and arbitrary array topologies and size. A proof of concept is supplied using a Galerkin-type numerical implementation of the proposed theory and is compared to the method of moment.