NIOBIUM-SIS MIXERS AT 490 GHZ, 690 GHZ AND 810 GHZ

Low noise mixers are developed for a dual channel heterodyne receiver for astronomical applications which will operate alternatingly in two of three the frequency bands 460-490 GHz, 660-690 GHz, and 800-850 GHz . As mixing elements Nb-Al2O3-Nb (SIS) tunnel junctions are used, fabr icated at the University of Cologne with integrated RF and IF circuitr y, also made of niobium. The frequency dependent RF-properties of the circuitry. are calculated for all bands using Mattis-Bardeen theory in the extreme anomalous limit. The circuits are optimized for a large i nstantaneous receiver bandwidth. to facilitate the use of waveguide ty pe mixer mounts without mechanical tuners. Results on receiver noise, stability and design accuracy will be presented.