The design and performance of a circularly polarized feed system for an 11 m diameter earth-station antenna, which operates in the frequency band 7.25 to 8.4 GHz, is described. A dominant factor in the design of the feed system is a requirement of <40 dB isolation at the centre of the band. To achieve this high isolation the feed system has several distinctive features, including low-reflection waveguide components and a matched radome on the feed horn. As well as meeting the isolation requirement, the feed system that is now installed in the earth station has an insertion loss >0.15 dB, an axial ratio >0.5 dB and a VSWR >1.3.
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