Rigorous analysis of crosspolarisation in flange-mounted rectangular-waveguide radiators

A rigorous Nh-order Rayleigh-Ritz variational solution to the problem of a flange-mounted rectangular waveguide radiating into a halfspace is formulated. The analysis shows the importance of including higher-order modes whose electric fields are polarised orthogonally to the dominant mode. The mechanism of coupling from the dominant mode to the higher-order modes is discussed and numerical results for the aperture admittance are given.