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IEEE Transactions on Microwave Theory and Techniques

A technique for noise measurements of SIS receivers

Qing Ke, M. J. Feldman

Published Apr 1, 1994• 36 citations
Publisher

Abstract

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.>

DOI
10.1109/22.285091

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An ultra low noise SIS receiver has been prepared for radio astronomy. The minimum double sideband receiver noise temperature is about 30 K which corresponds to 2 /spl planck//spl omega//k or an equivalent number of 4 photons of noise. The minimum measured double sideband mixer noise temperature is about 10 K which corresponds to 0.6 /spl planck//spl omega//k or approximately to 1 photon of noise. The fixed tuned SIS mixer operates in the 290-370 GHz frequency range. The submicron niobium junctions mere fabricated using photoresist lines for junction definition. The receiver has been used at the 30 m IRAM radio telescope in Spain in winter 1994. Telescope system noise temperature of 500 K single sideband has been achieved when the sky opacity was about 0.17.>

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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.>
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The development of quantum limited heterodyne receivers requires that you understand and are able to measure the major sources of noise in the receiver system. The major sources of noise in millimeter- and submillimeter-wave SIS heterodyne receivers are the optical front end losses, vacuum fluctuation noise associated with the RF coupling efficiency to the SIS tunnel junction and IF amplifier noise. Although there are several methods for estimating the optical losses and IF amplifier noise, the RF coupling efficiency or quantum efficiency has been much more difficult to ascertain. This paper describes in situ techniques for measuring all three noise contributions in a standard receiver used for astronomical observations. Results are presented for the receivers operating in the Owens Valley Millimeter Interferometer Array.>
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.>
We have studied the sensitivity of a superconducting NbN hot electron bolometer mixer integrated with a spiral antenna at 4.3 THz. Using hot/cold blackbody loads and a beam splitter all in vacuum, we measured a double sideband receiver noise temperature of 1300 K at the optimum local oscillator (LO) power of 330 nW, which is about 12 times the quantum noise (hν/2kB). Our result indicates that there is no sign of degradation of the mixing process at the super-THz frequencies. Also, a measurement method is introduced where the hot/cold response of the receiver is recorded at constant voltage bias of the mixer, while varying the LO power. We argue that this method provides an accurate measurement of the receiver noise temperature, which is not influenced by the LO power fluctuations and the direct detection effect. Moreover, our sensitivity data suggests that one can achieve a receiver noise temperature of 1420 K at the frequency of [OI] line (4.7 THz), which is scaled from the sensitivity at 4.3 THz with frequency.
The receiver noise temperature of THz superconductor-insulator-superconductor (SIS) receivers is composed of several contributions, in which the input RF noise is usually not negligible. In this paper, we investigate the input RF noise (Trf) of a waveguide superconducting niobium nitride (NbN) SIS receiver operating at 0.5THz. In particular, the input RF noise is measured for two respective cases of a small beam aperture surrounded by an aluminum plate and a blackbody, which is located just in front of the 0.5THz NbN SIS receiver. Detailed measurement results will be presented.
An ultra low noise SIS receiver has been prepared for radio astronomy. The minimum double sideband receiver noise temperature is about 30 K which corresponds to 2 /spl planck//spl omega//k or an equivalent number of 4 photons of noise. The minimum measured double sideband mixer noise temperature is about 10 K which corresponds to 0.6 /spl planck//spl omega//k or approximately to 1 photon of noise. The fixed tuned SIS mixer operates in the 290-370 GHz frequency range. The submicron niobium junctions mere fabricated using photoresist lines for junction definition. The receiver has been used at the 30 m IRAM radio telescope in Spain in winter 1994. Telescope system noise temperature of 500 K single sideband has been achieved when the sky opacity was about 0.17.>