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European Microwave Conference (EuMC)

Superconducting Tunnel Junction Noise Generator and SIS Mixers Noise Measurements

Victor Y. Belitsky, V. P. Koshelets, I. L. Serpuchenko, Michael A. Tarasov, Lyudmila V. Filippenko, S. V. Shitov

Published Oct 1, 1990• 3 citations
Publisher

Abstract

In this work the output noise calibration of cryogenically cooled low noise SIS mixers, direct detectors and IF amplifiers by means of SIS noise source was studied experimentally. Applying LO power sufficient to linearize IV curve of SIS one may vary noise temperature from 4,2 to 100 K by changing bias current. Shot noise in series arrays of SIS junctions differs from noise in single junction.

DOI
10.1109/euma.1990.336144

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In this work the output noise calibration of cryogenically cooled low noise SIS mixers, direct detectors and IF amplifiers by means of SIS noise source was studied experimentally. Applying LO power sufficient to linearize IV curve of SIS one may vary noise temperature from 4,2 to 100 K by changing bias current. Shot noise in series arrays of SIS junctions differs from noise in single junction.
Cryogenic noise measurements are typically carried out using a variable-temperature load or a commercial noise diode in conjunction with a cryogenically-cooled attenuator. In both of these cases, thermal gradients can present a significant source of uncertainty. In the astronomy community, SIS mixers biased beyond their gap voltage are often used as shot-noise sources and employed to determine the noise of IF amplifiers. In this work, a tunnel junction with metal electrodes is used as noise source for characterization of cryogenic amplifiers. It is shown that this method is easily calibrated and can provide results that agree well with those obtained using the cold-attenuator method.
The dominant source of noise in an SIS mixer is the noise in the photon-induced current. We have made accurate measurements of noise induced in SIS junctions by 95 GHz photons. The noise is measured at 1.5 GHz using a low-noise cryogenic measurement system. The measured photon-induced noise is compared to the noise predicted by Tucker's theory augmented by a vacuum/thermal noise term. For small to moderate rf powers, at which SIS mixers are operated, the measured noise is nearly perfectly predicted by this theory for all the devices measured. Measurements of series arrays of SIS junctions also agree with this theory showing that the noise of each SIS junction in the array is independent. At large rf powers, the measured noise was higher than the predicted noise, in devices with smaller capacitance. We also measured the noise in single junctions and arrays with no rf radiation. These measurements agreed very well with the predicted shot noise for most bias conditions.>
Cooled low noise amplifier (LNA) is used as the first or second component of receiver system in radio astronomy. It is developed all over the world to improve its noise. Noise temperature is one of the most important parameters of LNA because it governs the observation time. It is usually measured by inputting two reference signal which have different power each other and measuring the responses. For accuracy, the power of these reference signals is required to be close to the noise of the LNA. In the conventional method output of a Avalanche diode is attenuated to 1/100 by a cold attenuator and used as a reference signal. In this method the error caused by the attenuator and the cable between the Avalanche diode and LNA is too large (a few 10 %) and another accurate noise measurement method is required. In this research we propose a new method using Superconductor-Insulator-Superconductor junction (SIS) as a reference signal. When biased, SIS generates small shot noise that is proportional to the bias voltage so it can be used as a reference signal that make an accurate noise measurement possible (a few % error). First, SIS and SIS housing is designed and fabricated for the shot noise to transmit without any loss and reflection. Then, noise temperature of the LNA is measured by using the conventional method and SIS shot noise method and compared. As a result, there was difference and it was shown that the capacitance of SIS is one of the candidate cause.
We have completed our theoretical and experimental investigations of the noise properties of superconducting tunnel junction (SIS) mixers operated as both a phase insensitive linear amplifier and as a phase sensitive linear amplifier. We proposed a technique by which a SIS mixer could be operated as a phase sensitive linear amplifier, i.e., the gain and noise temperature of the amplifier are a function of the phase of the incoming signal. In this technique two phase coherent local oscillators at different frequencies are combined in the mixer simultaneously so both a phase preserving and phase conjugating mixing process occur resulting in a phase sensitive mixer.
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.
A quantum-statistical analysis of the signal and noise performance of the quasiparticle (SIS) heterodyne mixers is presented. In contrast with the earlier theories, the quantum properties of the signal source have been taken into consistent consideration. In the quantum range of sensitivity the noise properties of the mixer can be characterized by the noise parameter ΘNintroduced earlier for the parametric amplifiers. Using the conventional 3-port model of the mixer circuit and the microscopic theory of the superconducting tunnel junctions we have obtained a general expression for ΘNand evaluated it numerically for various quasiparticle current step widths, dc bias voltages, local oscillator powers, signal frequencies ωs, signal source admittances Ysand operation temperatures T. In a reasonable range of these parameters,\Theta_{N}^{DSB}has turned out to be less than the so-called quantum limith\omega_{s}/2. On the contrary, in the single sideband mode of the mixer performance, ΘNis always larger thanh\omega_{s}/2. The difference between the two modes of operation is discussed from the point of view of the quantum theory of measurements.