A low noise 230 GHz heterodyne receiver employing 0.25- mu m/sup 2/ area Nb-AlO/sub x/-Nb tunnel junctions

The authors report recent results for a full-height rectangular waveguide mixer with an integrated IF matching network. Two 0.25 mu m/sup 2/ Nb-AlO/sub x/-Nb superconducting-insulating-superconducting (SIS) tunnel junctions with a current density of approximately=8500 A/cm/sup 2/ and omega RC of approximately=2.5 at 230 GHz have been tested. One of these quasiparticle tunnel junctions is currently being used at the Caltech Submillimeter Observatory in Hawaii. Detailed measurement of the receiver noise have been made from 200-290 GHz for both junctions at 4.2 K. The lowest receiver noise temperatures were recorded at 239 GHz, measuring 48 K DSB at 4.2 K and 40 K DSB at 2.1 K. The 230-GHz receiver incorporates a one-octave-wide integrated low-pass filter and matching network which transforms the pumped IF junction impedance to 50 Omega over a wide range of impedances.<
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