Dual channel 115 and 230 GHz SIS receivers in operation at the Owens Valley Radio Observatory

The Owens Valley Radio Observatory millimeter-wave interferometer array is presently operating with dual-channel SIS (superconductor-insulator-superconductor) tunnel junction receivers. The first channel covers the frequency range from 85 to 120 GHz and the second channel covers the frequency range from 200 to 300 GHz. The mixers consist of a corrugated feed horn, a single-stage circular-to-rectangular waveguide transition a reduced-height waveguide with an SIS junction mounted across the E-plane, and a non-contacting backshort. The mixer block has a built-in RF choke for the IF (intermediate frequency) signal path which is designed to present a short circuit to the junction at frequencies above the 2-GHz IF frequency. The small-area (<1 μm²) PbInAu-native oxide-PbAu SIS tunnel junctions are fabricated using a bridge lift-off technique. The receivers in the 85- to 120-GHz band have noise temperatures of <100 K, while the receivers in the 100- to 300-GHz band have noise temperatures in the range from 200 to 300 K. These dual-channel receivers are mounted in 4.5 K closed-cycle refrigerators and are in continuous use on the array