Development of wideband feed for Kashima 34 m antenna

Corrugated horns are the most typical feeds used in radio telescopes. They have typical fractional bandwidths of almost 20–30%. In very long baseline interferometer observations, the feed, low-noise amplifiers, and backend electronics limit the bandwidth of the whole receiver system. Wider bandwidth translates into better sensitivity, and in greater signal-to-noise ratio. This will allow finer resolution of group delay time or shorter observation times in geodetic observations. Recently, the bandwidth of the backend digital samplers in our receiver system was increased up to 16 Gsps. At that time, the feed antenna became the component limiting the instantaneous bandwidth of our very long baseline interferometry receiver system. Various wideband feeds have been developed in past years. However, none of them meets the needs of our Kashima 34 m Cassegrain antenna, which requires feeds with narrow beam width. This paper reports on newly developed wideband feeds for our 34 m antenna, which have been successfully used in the 6.5–15 GHz band with 30–50% aperture efficiency.