The problem of substructure characteristic modes is developed using a scattering matrix-based formulation, generalizing subregion characteristic mode decomposition to arbitrary computational tools. It is shown that the modes of the scattering formulation are identical to the modes of the classical formulation based on the background Green's function for lossless systems under conditions where both formulations can be applied. The scattering formulation, however, opens a variety of new subregion scenarios unavailable within previous formulations, including cases with lumped or wave ports or subregions in circuits. Thanks to its scattering nature, the formulation is solver-agnostic with the possibility to utilize an arbitrary full-wave method.

翻译：本文基于散射矩阵公式发展了子结构特征模式问题，将子区域特征模式分解推广至任意计算工具。研究表明，在两种公式均可应用的条件下，散射公式的特征模式与基于背景格林函数的经典公式特征模式在无耗系统中完全一致。然而，散射公式开启了先前公式无法涵盖的多种新子区域场景，包括集总端口或波导端口情形以及电路中的子区域。得益于其散射特性，该公式与求解器无关，可利用任意全波方法进行计算。