Design of Sloping Septum Polarizers using Coupled Wave Equations

Abstract

Converters between circular and linear polarisation are of great interest e.g. in satellite communications. The operation bandwidth of waveguide polarizers with cylindrical pure metal or pure dielectric inserts can be increased by combining both /1/ Pure metal inserts, however, are advantageous at high temperature variations as in outdoor units. Stepped metal septum polarizers can be designed to give near 0 dB ellipticity over medium bandwidth /2/. Sloping metal septum polarizers are assumed to give only bandwidths up to 5 % /2/. But they seem desirable for high return loss. In /3/ it is shown that the behaviour of stepped septum polarizers can be calculated by using mode matching techniques to obtain the generalized scattering matrix of each step. The modal fields of the ridge waveguide eigenvalue problem have to be known. Although it is on principle also possible to calculate sloping septum polarizers with this method by treating them as stepped ones with many very small steps /3/, this does not seem convenient because of the computational effort.