Low noise broadband tunerless waveguide SIS receivers for 440-500 GHz and 630-690 GHz

We have developed broadband SIS heterodyne receivers for the frequency ranges from 440 to 500 GHz and 630 to 690 GHz. The mixerblocks contain a punched waveguide cavity which forms a fixed backshort. The substrate channel is sawed across the waveguide. The horn antenna is flanged to the mixerblock. The blocks are easy and quickly to manufacture even for the small dimensions needed in the submm wavelength range. We use Nb-Al2O3-Nb junctions with areas of 0.8 mu m(2) and integrated three step niobium tuning structures. With this design we achieve instantaneous double sideband receiver noise temperatures around 120 K over the frequency range from 660 to 690 GHz and around 80 K from 440 to 500 GHz. The mixer performance agrees well with the design calculations for the tuning structures.