Rigorous hybrid field theoretic design of stepped rectangular waveguide mode converters including the horn transitions into half-space

A full-wave hybrid field-theoretic method is presented for accurate and efficient computer-aided design of complete microwave or millimeter-wave radiating components comprising stepped rectangular-waveguide mode converters and horn transitions including the effect of the aperture radiating into half-space. The method combines the complete six-field-component modal S-matrix formulation, for the double-plane waveguide discontinuity problem of the throat section, with the full-component moment solution for the aperture problem. Two orthogonally polarized sets of rooftop basis functions are utilized to model the magnetic surface currents in the apertures. All important design parameters are rigorously taken into account by the design theory. The method is verified by comparison with available measured data for pyramidal horn transitions. Two design examples for stepped multimode horn transitions are presented. One example has been optimized with regard to pattern symmetry and achieves nearly identical E- and H-plane patterns from 10.8 to 11.2 GHz. The second example with optimized cross-polarization behavior shows -50-dB maximum cross-polarization level at 11 GHz