Generalized Surface-Integral-Equation-Based Sub-Structure Characteristic-Mode Solution to Composite Objects

Characteristic mode analysis (CMA) is becoming a popular tool to analyze radiation and scattering problems. However, some preliminary studies revealed that the conventional full-structure characteristic modes (CMs) had troubles identifying the desirable modal solutions to some antenna problems, e.g., dielectric resonator antennas (DRAs) with a finite ground plane. In order to remedy the drawback of full-structure CMs and then expand the application scope of CMA, we herein propose a generalized surface integral equation (SIE)-based sub-structure CM formulation for composite objects with arbitrary metallic-dielectric combinations. For the computation of sub-structure CMs, the composite object is handily decomposed into two parts with different functions, namely, the main radiator and passive loading. The distinctive feature of the sub-structure CMs is to accurately capture the resonant modes that belong to the main radiator in the presence of the passive loading. Numerical results of several typical antennas validate that the sub-structure CMs can provide flexible and useful modal solutions to some antenna problems in which the resonant modes confined to designated regions are desirable.