On the use of cavity modes as basis functions in the full wave analysis of printed antennas

Magnetic wall cavity (MWC) modes are often employed as basis functions in the method of moments (MoM) full wave analysis of printed antennas, especially in its spectral domain version, where the use of entire domain basis functions is particularly convenient, but in some cases the TE (solenoidal) modes are not included. Here we investigate on the effect of this exclusion, explaining the nature of the TE-TM coupling, presenting criteria to determine the necessary number of modes, and giving numerical results for annular patches, especially relevant in this context.