New Tunable Iris-Post Square Waveguide Polarizers for Satellite Information Systems

This paper presents new tunable square waveguide polarizers for satellite information systems. The wide operation frequency band is provided by the application of irises to obtain good matching and polarization characteristics simultaneously. The tuning option is provided by utilization of antiphase posts in the design. The height of the posts can be variable. This allows fine tuning of the differential phase shift between the fundamental modes with vertical and horizontal polarizations at the output of a waveguide polarizer. The structures of polarizers were divided into identical iris-post section. The section was analyzed using wave matrices technique and its characteristics were optimized. The general transfer matrix of the polarizer was obtained as the product of transfer matrices of iris-post waveguide sections and of equivalent transmission lines. Two designs of polarizers were developed for the operating X-band 7.7-8.5 GHz. The polarizer with two 45° sections provides voltage standing wave ratio less than 1.23 for both horizontal and vertical polarizations. Introduced differential phase shift is 90° ± 3.25°. Simulated axial ratio is less than 0.5 dB. The corresponding crosspolar discrimination is higher than 31 dB. Developed polarizer with three 30° sections provides voltage standing wave ratio less than 1.17 for both polarizations. The differential phase shift lies within the range 90° ± 2.2°. Simulated axial ratio is less than 0.34 dB. The corresponding crosspolar discrimination is higher than 34 dB. New tunable iris-post square waveguide polarizers can be applied in modern communication systems.