Review and Generalization of the Orthogonality of Scattering Characteristic Modes

Scattering characteristic modes (CMs) are a set of independent and complete fundamental working modes of the objective scatterer. The CMs satisfy a series of valuable features, such as the energy decoupling feature expressed as field-current interaction and the field-field orthogonality feature expressed as field-field interaction. The features have become the theoretical foundation of the CM-based engineering applications. In this paper, both the energy decoupling and field-field orthogonality features are simply reviewed first, and then the field-field orthogonality feature is further generalized.