Generalized Characteristic-Mode Formulation for Composite Structures With Arbitrarily Metallic–Dielectric Combinations

Two types of generalized characteristic-mode (CM) formulations are proposed for the modal analysis of composite structures with arbitrarily metallic-dielectric combinations. The contact-region modeling (CRM) technique is introduced to conveniently model an arbitrary composite electromagnetic (EM) structure as a combination of relatively simple single region. The proposed generalized CM formulations eliminate many difficulties in previously published CM theories, where PEC bodies should be fully coated with dielectric layers or dielectric layers must be infinitely large in the 2-D plane. Specially, the CRM technique allows flexibly modeling arbitrarily combined metallic and dielectric regions using the electric-field integral equation (EFIE) and the PMCHWT equation, respectively. By enforcing field continuity conditions on various region interfaces, the EFIE-PMCHWT surface integral equation results in two generalized eigenvalue equations for characterizing the resonant behaviors of arbitrarily composite structures. It is demonstrated that the resultant eigenvalues indicate the ratio of the stored and radiated power of each CM. Moreover, the corresponding modal currents and modal fields clearly explain the underlying radiation or scattering mechanisms of EM problems. The numerical results for typical composite metallic-dielectric structures are presented to illustrate the accuracy of the proposed CM formulations.