Field theory design of a corrugated septum OMT

The authors present a rigorous design method for corrugated septum orthomode transducers (OMTs) which combines the compactness advantage of the stepped septum structure with the phase matching potential of corrugated waveguide polarizers. The structure under investigation is composed of standard field theory key-building blocks, the double-step discontinuity, the waveguide-to-ridged-waveguide transition, and the transition waveguide to septated waveguide. Based on the modal scattering matrix method, the design takes into account the influence of both the finite septum thickness and the higher-order mode interaction at all discontinuities. Computer-optimized design data are given for a Ku-band waveguide corrugated septum polarizer, achieving a return loss of more than 20 dB together with a 90 degrees +0 degrees /-3 degrees differential phase shift for about 10% bandwidth. The theory is verified by measurements.<>