A Very Low Noise Quasiparticle (SIS) Mixer Receiver for Radio Astronomical Applications

A Superconducting quasiparticle mixer receiver for 35-50 GHz is described. An array of six Pb In-oxide-Pb0.7Bi0.3 tunnel junctions with 40 ¿ array normal resistance and a shunt capacitance of 0.2 pF is used. The mixer is immersed into liquid helium and operated at 2 K. A 3.7-4.2 GHz parametric amplifier, also at 2 K is used as the if amplifier. The high if frequency allows single sideband operation with a system noise temperature of 140 K at 47 GHz. A lens guide is used for guiding the signal from the Cassegrain telescope focus to the liquid helium cooled lens corrugated horn and the mixer. The SSB system noise temperature varies rather smoothly from ¿ 220 K at 35 GHz to ¿ 140 K at 50 GHz suggesting that quantum gain effects are becoming more important at the high frequency end. The receiver is operational in the 20 m mm-wave telescope at the Onsala Space Observatory.