Presentation #316.02 in the session “Radio and mm Instrumentation and Surveys”.
This project simulates the S11 and efficiency of an ultra-wideband receiver for the GBT under various material conditions of the feed’s quartz window. The goal was to improve the impedance match across the window by reducing the thickness of high-dielectric quartz needed to meet the strength requirements of the system. Instead, an intermediate layer of low-dielectric support foam sandwiched between two thin layers of quartz was used to improve power transmission without compromising feed efficiency. The support foam was tested at two thicknesses and two locations within the mouth of the feed horn, testing five values of the dielectric constant of the foam at each thickness and location. It was ultimately determined that the location of the window within the horn is a more significant factor than either the thickness or dielectric constant of the foam; a low dielectric foam at a thickness of two inches at the location of the feed’s thermal gap provides comparably improved S11 results relative to a window with one inch thick foam under the same conditions, but a much greater and more stable improvement to the overall efficiency of the feed.