DESIGN AND ANALYSIS OF A WAVEGUIDE SIS MIXER ABOVE THE GAP FREQUENCY OF NIOBIUM

摘要

We present the design and experimental data of an SIS waveguide mixer for frequencies from 760 to 820 GHz. We use a Nb-A^CVNb junction with an integrated niobium tuning structure. The waveguide mixer block contains no adjustable tuning elements. Design criteria for lossy tuning structures, differing from the impedance matching techniques used in the lossless case, are described. We separate the influence of the intrinsic mixing properties of an SIS junction from the effects of the power coupling to the signal source on the overall noise. This allows us to derive the contributions of the optics, the losses in the stripline and the noise generated in the junction to the total receiver noise from the measurements. We achieve double sideband receiver noise temperatures of around 850 K at frequencies from 780 to 820 GHz and 4.2 K operating temperature of the mixer. Cooling the mixer to 2.5 K results in an improvement of the receiver noise temperature by 150 to 200 K. The bandwidth is presently limited by the local oscillator. The mixer was successfully used in a dual channel receiver (440 to 490 GHz and 780 to 820 GHz) at the Submillimeter Telescope Observatory (SMTO) on Mount Graham, Arizona.