The design of the MeerKAT UHF band feed

The design methodology and the expected performance results of the UHF band feed for the MeerKAT interferometer, which is a precursor to the Square Kilometer Array(SKA), are presented. The feed consists of a wide flare angle axially corrugated conical horn, a horn matching section, a compact orthogonal mode transducer (OMT) and an integrated directional coupler. The MeerKAT dish is a classical Gregorian offset dual-reflector antenna system. A hybrid optimization algorithm comprising of a global search algorithm, namely the Population-Based Incremental Learning algorithm, and a downhill method is used as optimizer for the horn design. The OMT and coupler were optimized with a downhill method. The predicted results show stable radiation patterns over the frequency band with an antenna efficiency above 71 % and a spillover temperature below 20 K at the lowest frequency. The efficiency increases to 78 % at the higher frequencies with a spillover temperature below 12 K. The feed's reflection coefficient is -20 dB and the feed's noise contribution to the system temperature, with the main contributors the OMT and the directional coupler, is below 1.5 K across the frequency band.