Quasi-optical slot antenna SIS mixers

Abstract-We describe quasi-optical SIS mixers op-erating in the submillimeter band (500-750 GHz) which have very low noise, around 5 hu/kB for the double-sideband receiver noise temperature. The mix-ers use a twin-slot antenna, Nb/Al-Oxide/Nb tunnel junctions fabricated with optical lithography, a two-junction tuning circuit, and a silicon hyperhemispher-ical lens with a novel. antireflection coating to optimize the optical efficiency. We have flown a submillimeter receiver using these mixers on the Kuiper Airborne Observatory, and have detected a transition of Hzl'O at 745 GHz. This directly confirms that SIS junc-tions are capable of low-noise mixing abwe the gap frequency. I