Characteristic Mode Analysis of Mutual Coupling

Mutual coupling between neighboring antennas is a major concern in the array design. Using the concept of characteristic modes, this work proposes a theoretical framework for the analysis of such electromagnetic interaction and its control mechanism. The root of interelement coupling lies in the mutually induced current in the neighboring elements. Henceforth, the initial part of this work concentrates on computing the coupled current by modeling the interaction of the uncoupled modes. Closed-form formulations have been derived for quantifying the coupling impacts. The proposed formulations have been further verified with numerical examples and method of moment-based commercial solver, such as Antenna Toolbox. Later, the theory of substructure modes has been combined with the theory of coupled characteristic modes to understand the perturbation in coupling behavior in the presence of ground plane or a parasitic element. A design strategy has been suggested to optimize the shape of the intermediate parasitic structure for controlling the coupled current in the neighboring elements. This current-based approach can find applications in different coupled scenarios such as antenna arrays or in printed circuit board components.