Wide-band low noise mm-wave SIS mixers with a single tuning element

Several SIS quasi-particle mixers have been designed and tested for the frequency range from 80 to 115 GHz. The sliding backshort is the only adjustable RF tuning element. The RF filter reactance is used as a fixed RF matching element. A mixer which uses a single 2 x 2 sq micron Pb-alloy junction in a quarter-height waveguide mount has a coupled conversion gain of G sub M(DSB) = 2.6 + or - 0.5 dB with an associated noise temperature of T sub M(DSB) = 16.4 + or - 1.8 K at the best DSB operation point. The receiver noise temperature T sub R(DSB) is 27.5 + or - 0.8 K for the mixer test apparatus. This mixer provides a SSB receiver noise temperature below 50 K over the frequency range from 91 to 96 GHz, the minimum being T sub R(SSB) = 44 + or - 4 K. Another mixer with an array of five 5 x 5 sq micron junctions in series in a full-height waveguide mount has much lower noise temperature T sub M(DSB) = 6.6 + or - 1.6 K, but less gain G sub M(DSB) = -5.1 + or 0.5 dB.