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Abstract

The next generation of radio receivers for astronomy will be marked by tenfold improvements in sensitivity. These sensitive receivers will be useful for the detection of broadband fast radio bursts and other transients as well as the efficient discovery of radio recombination lines among many other scientific pursuits. One contribution to these improvements is an increase to decade receiver bandwidths. The Green Bank Observatory (GBO) is currently in the process of fabricating a new ultra-wideband (UWB; 0.7 to 4.2 GHz) receiver for the Green Bank Telescope (GBT). The UWB receiver will be used by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) to perform pulsar timing experiments using the GBT with greater sensitivity than before. The design of the receiver features a quad-ridged, flared feed horn and utilizes a corrugated skirt and a quartz spear to extend the receiver's bandwidth to 6:1. Through modeling and performance simulation, we find the predicted efficiency of the receiver to be around 60–70% at lower frequencies and above 50% at higher frequencies. The S11 values for the UWB receiver are better than –10 dB across the entire bandwidth, and performance is only predicted to degrade slightly at 2.8 GHz with the inclusion of a waveguide window.

In an effort to determine the potential cause of reduced efficiency as a function of frequency, we perform an analysis of waveguide mode excitation to determine the concentration of higher-order mode excitation in the aperture of the receiver. Preliminary results suggest that higher-order mode (i.e. TM12 and TM13) excitation is present at higher frequencies, but we cannot conclude that it is the sole cause of reduced feed efficiency at those frequencies.

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