Development of an SIS junction mixer over 120-180 GHz band

We have developed a fixed-tuned SIS (superconductor-insulator-superconductor) mixer across 120-180 GHz band. This mixer employs an SIS chip fabricated by Nobeyama radio observatory which consists of a series array of 6 Nb/Al-Al₂O₃/Nb junctions in a microstrip line on a fused quartz substrate. The SIS chip is placed at the center of the half-height waveguide mixer mount to have a good incoming signal coupling over the whole frequency band. No mechanical tuner was used in the SIS mixer and the RF signal and local oscillator power are injected to the mixer via a cooled cross-guide coupler. We measured double sideband noise temperatures of a receiver using the SIS mixer, which is 32-131 K over 120-180 GHz band. The developed SIS mixer is now in use for radio astronomical observations on the TRAO 14-m radio telescope.