A 345-GHz Sideband-Separating Receiver Prototype With Ultra-Wide Instantaneous Bandwidth

In this article, we present a sideband-separating (2SB) receiver prototype for operation between 300 and 360 GHz with ultra-wide instantaneous bandwidth. This was achieved using wide-bandwidth superconductor–insulator–superconductor (SIS) mixer designs and intermediate frequency (IF) components, including a multioctave IF hybrid placed outside the cryostat. We tested the prototype with a three-junction SIS device from the wideband Submillimeter Array high-band receiver, as well as a newly designed one-junction device. Our measurements demonstrated that the prototype receiver had a usable IF range of 4–13 GHz with the one-junction device and 4–17 GHz with the three-junction device. The measured single-sideband (SSB) noise temperatures were 96 $\,\pm \,$ 8 K from 312 to 363 GHz with the one-junction device and 109 $\,\pm \,$ 14 K from 314 to 367 GHz with the three-junction device. Over the same frequency range, the image rejection ratio was above 12.3 and 11.0 dB for 90% of the data points with the one-junction and three-junction devices, respectively. We have identified methods to further enhance the performance of this prototype and we believe that an upgraded receiver can provide a usable IF bandwidth up to 4–20 GHz.