Multi-frequency dual polarisation radiometer common aperture antenna feeding system

This study presents a design of a tri-band dual polarisation common aperture feed horn used for the radiometer. The proposed feeding system is made up of a corrugated horn, an orthomode transducer (OMT) and two pairs of a high-pass filter (HPF) and a band-pass filter (BPF). The broadband profiled corrugated horn loaded with teeth (rings) is adopted as the feed of the radiometer. Wideband finline OMT is developed to realise a bandwidth ratio in excess of 2:1. Two different HPFs and BPFs are employed to block and pass waves of different frequencies. The feeding structure is then simulated, fabricated and tested. The measured results show that the radiation patterns possess good symmetry at all three working frequencies of interest (18.7, 23.8 and 37GHz). Furthermore, the cross-polarisation levels are below -23dB and voltage standing-wave ratios are lower than 1.5 throughout all working bands.