  Conventional surface integral equation (SIE)-based characteristic mode
formulation for the patch antenna structure with a finite substrate is
susceptible to the spurious (nonphysical) modes due to the dielectric part. To
avoid the contamination of spurious modes, we propose a novel generalized
eigenvalue formulation based on the electric field integral equation coupled
Poggio-Miller-Chang-Harrington-Wu-Tsai (EFIE-PMCHWT) equation. In this
formulation, the real and imaginary parts of the exterior integral operators
are chosen to construct the finalized weighting matrices, to connect radiated
power of the characteristic current. Compared with other SIE-based methods,
this equation doesn't need additional post-processing since it can effectively
avoid spurious modes. Numerical results compared with the volume-surface
integral equation (VSIE) are investigated to validate the accuracy.
