Development of passive microwave antenna-feed systems for wide-band dual-polarisation receivers

This study presents the design and experimental results of a wide-band passive antenna-feed system developed for the C-band dual-circular-polarisation receiver of the Sardinia radio telescope (SRT). The latter is a 64 m diameter shaped radio-telescope under construction designed to operate with high efficiency from 300 MHz to over 100 GHz. The developed C-band antenna-feed system exhibits very high performances in a 30 band centred at 6.7 GHz, for example the return loss at all electrical ports is higher than 30 dB and the cross-coupling between the two polarisations is lower than 34 dB. The design solutions of all the feed-system components such as marker injector, polariser, transitions and the ortho-mode transducer (OMT) are reported in the study. In particular, the novel architecture of the OMT that provides an isolation between the two rectangular ports better than 70 dB is described in close detail. Computed and experimental results regarding both the complete system and its sub-assemblies are reported and discussed.