Power Transport Theorem (PTT)- Based Decoupling Mode Theory (DMT) for Wave-Port-Fed Transmitting Antennas

Using the work-energy theorem based physical interpretation for characteristic mode theories (CMTs), it is exposed that: strictly speaking, the existing CMTs are the modal analysis theories for the externally-incident-field-illuminated scattering objects and the lumped-port-driven electromagnetic structures, but not for the wave-port-fed transmitting antennas, so they cannot provide an exact modal analysis to the wave-port-fed antennas. This paper will propose an effective modal analysis theory for the wave-port-fed antennas. Power transport theorem (PTT), which governs the transport process of the power-flow passing through the wave-port-fed antenna, is derived. It is found that the input power term contained in the PTT is the source to sustain the steady power transport. Under the PTT framework, a novel modal analysis theory-decoupling mode theory (DMT)-is proposed for the antenna. By diagonalizing the input power operator (IPO), the PTT-based DMT can construct a set of energy-decoupled modes (DMs) for the antenna. The DMs-based modal expansion satisfies the Parseval's theorem, and the Parseval's theorem implies that: for any mode, its time-domain, frequency-domain, and spectrum-domain energies are the same. A novel concept of "electric-magnetic energy-decoupling factor" is introduced for quantifying the decoupling degree between the modal electric and magnetic fields. A field-based definition for the modal input impedance and admittance is proposed as an alternative for the conventional circuit-based definition.