System noise performance of ultra-wideband feeds for future radio telescopes: Conical-Sinuous Antenna and Eleven Antenna

Next generation radio telescopes can greatly benefit from reflector antenna feeds that demonstrate very wide frequency bandwidth and can potentially realize low noise performance of the receivers. In this paper, we provide an overview of the current developments at the national radio observatories in Sweden and USA that make use of novel multi-port antenna feeds, such as the Sinuous Antenna and Eleven Antenna. The focus of this overview is on the system performance, when using this technology at high or very low frequencies, i.e. when the feed-receiver system is fully or partially (cryogenically) cooled.