Sensitive broadband SIS receivers for microwave limb sounding

We present the measured performance of a sensitive new broadband waveguide sideband-separating superconductor-insulator-superconductor (SIS) heterodyne receiver with very wide IF bandwidth that is being developed for a future space-borne microwave limb sounder to study the earthpsilas atmosphere. The prototype receiver has measured noise temperature below 100 K from 190 to 300 GHz, and features 24 GHz of sideband-separated output. Measured sideband image rejection is typically 13 dB. The receiver features a three-section suspended stripline 6-18 GHz quadrature hybrid coupler integrated into the mixer waveguide block to minimize phase errors and standing waves to provide maximum bandwidth and image rejection. The high spectral resolution achieved with heterodyne detection will enable precision measurement of the profiles of pressure-broadened thermal emission spectral lines. Broad instantaneous bandwidth will enable multiple chemical species in the atmosphere to be measured simultaneously without retuning the receiver.