Remote controlled horn/lens feed for a 25 metre radio telescope

A remotely controllable L band feed system was required for three 25 metre diameter radio telescope antennas, which form part of the MERLIN array in UK. A combined horn and lens feed system has been designed. In order to avoid compromising other feed systems on the same antenna the lens is stowed away when not in use. Details are given of the optical design approach as well as the mechanical functionality and manufacturing methods. Three complete systems have been manufactured and installed on radio telescopes; test methods and measured results are shown. Aperture efficiencies slightly in excess of 50% were obtained, which is excellent for an L band feed on this type of 25 metre cassegrain antenna. System noise temperature results were a little disappointing, but there are clear pathways to improving this. All three feed systems have been used successfully for radio astronomical observations.