An Ultra-wideband Feed Horn for the Green Bank Telescope

An ultra-wideband feed horn is designed and fabricated in the frequency range 0.7 to 4 GHz. The scientific goals are to improve pulsar timing observations by allowing continuous coverage of the band. Given the GBT optics, mechanical limitations constrain the optimization of the maximum aperture efficiency to minimum system noise temperature ratio. To achieve these goals a quad-ridge design is selected. A technique is developed for the manufacture of a low loss vacuum window with adequate strength and low permeability. Measurements of the far field patterns, noise temperature and GBT system equivalent flux density are compared to model-based predictions. Modifications of the ridge profiles to control the modal content and improve efficiency are explored.