Overview on the Modal Orthogonality of the Wave-Port-Fed Transmitting Antennas

The fundamental physical principle and core mathematical formulations of the energy transport theorem (ETT)-based decoupling mode theory (DMT) for analyzing the energy-decoupled modes (DMs) of the wave-port-fed transmitting antennas are reviewed. The various frequency-domain and time-domain orthogonality satisfied by the transmitting DMs are summarized. The physical meanings of some important orthogonality are explained. The dependence relationships among the various orthogonality are revealed. The necessity and importance of the imaginary power orthogonality is emphasized. From the perspective of modal orthogonality and some other perspectives, the essential differences between the ETT-based DMs and the sub-structure integral equation (SS-IE)-based characteristic modes (CMs) are clarified.