Electromagnetic Modal Analysis for Multiple- Ports-Fed Antenna Array: From Waveguide-Array Integrative Analysis to Amplitude-Phase Factor Method

For the antenna array fed by single wave port, the energy transport theorem (ETT)-based modal analysis method can effectively calculate its energy-decoupled modes (DMs) by diagonalizing the input power operator (IPO). Besides the single-port-fed antenna array, the ETT framework and the diagonalizing IPO method are also applicable to the antenna array fed by multiple wave ports. However, before applying the diagonalizing IPO method to the multiple-ports-fed antenna array, the dependence relationship among the port currents must be integrated into the IPO, or the diagonalizing IPO method cannot give accurate results. Previously, a waveguide-array integrative modal analysis method was proposed to integrate the port-currents-dependence relationship into the IPO. However, the waveguide-array integrative analysis has a relatively large computational burden, and has no ability to obtain the inherent DMs of the antenna array itself. To overcome the abovementioned difficulties, this paper proposes a novel method to integrate the port-currents-dependence relationship into the IPO, when the ports have the same geometrical shape and size, and the only difference among the port currents is their amplitudes and phases. The fundamental ideas of the novel method are that: 1) to expand the port currents in terms of the same basis functions; 2) to relate the port currents with each other by multiplying some proper amplitude and phase factors to the basis function expansion coefficients. Thus, this paper calls the novel method amplitude-phase factor method to be distinguished from the previously proposed waveguide-array integrative analysis method.