On improvement of the radiation performance of the open-ended circular waveguide

The cross-polar performance is analyzed for radiation of the TE/sub 11/ mode from the open-ended circular waveguide of typical diameter of around one wavelength. The internal waveguide surface at the end is loaded with a finite longitudinally corrugated section with grooves filled with dielectric. The analysis is based on the mode-matching method combined with a factorization method, taking into account all the effects associated with wave scattering at the open end. It is shown that the width of the frequency band where the cross-polar level is not higher than -30 dB can potentially be made a few times wider in comparison with the 27% bandwidth corresponding to the ordinary circular waveguide. The influence of the higher-order modes excited at the aperture on the radiation performance is also discussed.