Power Transport Theorem Based Decoupling Mode Theory for Wave-Port-Fed Transmitting Antennas

Abstract

Employing the work-energy principle based physical interpretation for characteristic mode theories (CMTs), it is exposed that: strictly speaking, the existing CMTs are the modal analysis theories for incident-field-driven scattering objects and lumped-port-driven transmitting antennas, but not for wave-port-fed transmitting antennas, so they cannot provide an exact modal analysis to wave-port-fed antennas. This paper focuses on establishing an effective modal analysis theory for wave-port-fed antennas. Power transport theorem (PTT), which governs the transport process of the power-flow passing through wave-port-fed antenna, is derived. It is found out that the input power contained in PTT is the source to sustain a stationary power transport. Under PTT framework, a novel modal analysis theory — decoupling mode theory (DMT) — is established for the antenna. By orthogonalizing input power operator (IPO), the PTT-based DMT can construct a set of energy-decoupled modes (DMs) for the antenna. A novel concept of "electric-magnetic energy-decoupling factor" / "electric-magnetic phase-mismatching factor" is introduced for quantifying the coupling/matching degree between modal electric field and modal magnetic field. A field-based definition for modal input impedance and admittance is proposed as an alternative for the conventional circuit-based definition. Three somewhat different but not contradictory physical meanings of modal significance (MS) are summarized.