A full-band waveguide SIS receiver with integrated tuning for 75-110 GHz

The performance of a broadband SIS (superconductor-insulator-superconductor) receiver with no mechanical tuning elements was modeled and tested. The mixer mount had a broadband-waveguide-to-microstripline transition consisting of a four-step Chebyshev single-ridge transformer. The last step of the ridge connected the waveguide to a microstripline circuit. The on-chip circuit consisted of a microstripline that transmitted the RF and the local oscillator signals to the SIS mixer. Both the SIS element and the inductor had RF grounds provided by 90° radial stubs. The inductor tuned out the junction capacitance to allow operation over the full frequency band. The SIS element can be a single junction or series array using Nb-AlO_x-Nb trilayer tunnel junctions with areas as small as 0.5 μm² and V_m(2 mV)=39 mV. Preliminary results indicated a DSB receiver noise temperature of 65-80 K across the band measured at 4.4 K with an internal cryogenic RF hot/cold source and with T_if=21 K. With another device, a mixer noise temperature of 35 K at 100 GHz was achieved, increasing to 45 K at 79.5 and 110 GHz. Coupled mixer gain of up to +3 dB and negative dynamic resistance on the first photon step were observed. The lowest noise temperature was obtained for an untuned single-junction mixer at 80 GHz: T_R=41 K and T _M=20 K were measured