A 275–425-GHz tunerless waveguide receiver based on AlN-barrier SIS technology

receiver with a 3.5-8 GHz intermediate frequency (IF). As mixing element, we employ a high-current-density Nb-AlN-Nb superconducting-insulating-superconducting (SIS) tunnel junc-tion. Thanks to the combined use of AlN-barrier SIS technology and a broad bandwidth waveguide to thin-film microstrip transi-tion, we are able to achieve an unprecedented 43 % instantaneous bandwidth, limited by the receiver’s corrugated feedhorn. The measured double-sideband (DSB) receiver noise tempera-ture, uncorrected for optics loss, ranges from 55 K at 275 GHz, 48 K at 345 GHz, to 72 K at 425 GHz. In this frequency range the mixer has a DSB conversion loss of 2.3 ± 1 dB. The intrinsic mixer noise is found to vary between 17-19 K, of which 9 K is attributed to shot noise associated with leakage current below the gap. To improve reliability, the IF circuit and bias injection are entirely planar by design. The instrument was successfully installed at the Caltech Submillimeter Observator