CHARACTERIZATION OF A 680-760 GHZ SIS WAVE-GUIDE MIXER

A heterodyne waveguide receiver employing 1 mu m(2) Nb superconducting tunnel junctions with on chip integrated tuning structures is charact erized from 680-760 GHz. Several different types of integrated tuning structures are investigated. Lowest DSB receiver noise temperatures of 310 K at 709 GHz and 400 K at 720 GHz are measured. Analysis of the d ata shows that the loss of the superconducting tuning structures has a major influence on the overall receiver performance. A 25% reduction in receiver noise temperature is observed if the mixer is cooled from 4.2 K to 2 K, which we attribute to the reduced loss of the supercondu cting microstrip lines at lower temperatures. The calculated performan ce of the different tuning structures is shown to be in good agreement with the actual receiver noise measurements.