Optimum field theory design of stepped E-plane finned waveguide transformers of different inner cross-sections

A new design is presented for broadband double-stepped ridged and all-metal finned waveguide transformers. The design combines the advantage of constant ridge thickness with that of the optimum matching potential of different waveguide inner cross-section dimensions. Based on the modal scattering matrix method, the rigorous design takes into account the influences of both the finite-ridge or fin thicknesses and the higher-order mode interaction at all discontinuities. Computer-optimized design data are given for compact transformers for WR112 and WR42 input waveguides achieving a return loss of more than 33 dB for the whole waveguide band. The theory is verified by measurements.<>