An Alternative Substructure Characteristic Mode Formulation for Slot Antennas

In this paper, a novel sub-structure characteristic mode (CM) formulation is proposed for arbitrary slot antennas, by leveraging the equivalence principle and the pseudo-image method. Inspired by the advanced generalized theory of CM (GTCM), a sub-structure-oriented weighting matrix, based on the admittance matrix, is systematically defined. This definition enables the eigenvalues to exhibit significant physical interpretations in both lossless and lossy environments, identifying the resonance and radiation properties of the slot antennas. Modal analyses for three numerical examples are performed to demonstrate the validity and effectiveness of the proposed method. Thus, the presented CM formulation provides an alternative approach for guiding the design of slot antennas.