Effect of an applied magnetic field on the performance of a sis receiver near 300 GHz

We have successfully constructed and tested a superconductor-insulator-superconductor (SIS) receiver for operation at 265–280 GHz using 1 m² area Nb–AlO _x –Nb tunnel junctions fabricated at Stony Brook. The best performance to date is a double sideband (DSB) receiver noise temperature of 129 K at 278 GHz. We find that suppression of the Josephson pair currents with a magnetic field is essential for good performance and a stable DC bias point. Fields as high as 280 gauss have been used with no degradation of mixing performance. We illustrate the improvement in the intermediate frequency (IF) output stability with progressively increasing magnetic fields.