Novel Surface Integral Equation-Based Sub-Structure Characteristic Mode Formulations for Lossy Composite Objects

A novel surface integral equation (SIE)-based sub-structure characteristic mode (CM) formulation is proposed. By defining radiation and dissipation matrices appropriately, the eigenvalues of the sub-structure generalized eigenvalue equation (SSGEE) are always complex with clear physical insights. If the selected main radiator is lossless, the imaginary part of the eigenvalue represents the generalized modal radiation efficiency while the real part can directly reflect the resonance characteristic of each CM. If the selected main radiator is lossy, the generalized modal radiation efficiency can also be obtained through the proposed SSGEE and some other simple steps. Furthermore, the SSGEE based on the combined field integral equation (CFIE) has also been developed to address the difficulties of internal resonance in CM analysis. The proposed SSGEEs are valid for composite objects that touch each other by employing the contact-region modeling (CRM) method.