A Technique for Accurate Noise Temperature Measurements for the Superconducting Quasiparticle Receiver

Qing Ke, M. J. Feldman

We present a simple new technique to determine the noise temperature of the RF input section of a superconducting quasiparticle heterodyne receiver. This quantity is difficult to measure by existing methods. The new technique uses standard hot/cold-load measurements, and the precision should be as good as the hot/cold-load determination of receiver noise temperature. For most receivers, correction terms will be much smaller than the quantum temperature /spl planck//spl omega//k.>

A. I. Elant’ev, Boris S. Karasik

J. D. Gallego, M.W. Pospieszalski

Qing Ke, M. J. Feldman

The output noise temperature, rather than the standard input noise temperature, is shown to be the fundamental measure of the shot noise of the superconducting (SIS) quasiparticle mixer. This conclusion is based on extensive numerical computations of the properties of optimized SIS (superconductor-insulator-superconductor) receivers and also on analytic calculations with separate consideration of correlated and uncorrelated noise sources. The quantum theory of mixing is used to derive a simple analytic expression for the mixer output noise which is independent of frequency, and qualitatively explains the dependence of the output temperature on each of the receiver's operating parameters. The derivation leads to a novel understanding of the SIS mixer which, distinguishes between its correlated and uncorrelated noise sources. The authors predict T(receiver)=2*T(mixer) for many SIS receivers. Numerous experiments substantiate the analysis.>

I. Peterson

William R. McGrath, Antti V. Räisänen, P. L. Richards +2 more

We have constructed a 30-40 GHz test apparatus which allows us to measure the noise temperatures of SIS mixers with an accuracy of better than ±1K. This is a factor of six improvement over earlier measurements. The most accurate measurement made thus far of a mixer which uses a single Pb-alloy junction yielded Tm= 9.2 ± 0.9 K; and mixer gain: Gm= 0.240 ± 0.005. In addition, SIS mixers employing arrays of N = 1, 5, 10, 25, and 50 tunnel junctions in series have been tested. The input power required to saturate the array mixers was found to increase as N2and the gain and noise temperature of the array mixers were independent of N.