20/30GHz compact dual band circular polarizer for satellite feed systems

Abstract

A compact solution for a dual band OMT polarizer that avoids the use of additional iris loaded corrugated sections is discussed here. The proposed device is based on a conventional septum type polarizer-OMT in waveguide technology covering two separate bands, were an extension of its normal (rather narrow) frequency band of operation has been achieved to meet restringing specifications for the 20/30 GHz 5% fractional bandwidth satellite link communication bands. The septum type OMT-polarizer consists of three physical ports: two of them in rectangular waveguide and another common port in circular or square waveguide. A given signal coming from a rectangular port is split into two 3dB orthogonal signals at the common port with a time delay of 90º between them. This produces a circular polarized signal: a RHCP associated to one of the rectangular ports and a LHCP associated to the second rectangular port. This compact design exhibits good return losses (>25dB) at the rectangular and circular ports as well as high isolation (>40dB) between modes. Furthermore, axial ratio is kept as low as 0.5dB in both communication bands.