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IEE Proceedings - Microwaves Antennas and Propagation

Low noise SIS receiver performance using Pb alloy tunnel junctions

Steven R. Davies, Leslie T. Little

Published Jan 1, 1998• 0 citations
Publisher

Abstract

A receiver noise temperature of 61 K (DSB) has been measured for a superconductor–insulator–superconductor (SIS) heterodyne receiver operating at 232 GHz, the lowest value reported to date for such a receiver employing a lead alloy junction. Analysis of the losses of the receiver components yields mixer noise temperature and conversion loss, Tm = 24 K and Lm = 2.1 dB (DSB). These are compared with predictions based on 3-port quantum mixer theory, made using the measured characteristics of the junction and an equivalent circuit for the waveguide mixer mount deduced from scaled modelling experiments.

DOI
10.1049/ip-map:19982251

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A LOW NOISE 410-495 GHZ Nb/AI,OJNb SIS WAVEG

Gert J. de Lange, Junction Fabri

The noise and gain of a heterodyne waveguide mixer employing Nb/A120JNb superconducting tunnel junc- tions is measured in the 400-500 GHz frequency range. Three different arrays of two junctions in series are analyzed. An array with integrated tuning stubs has lowest receiver noise temperatures of T, = 120 K DSB at 480 GHz, which is to our knowledge the lowest value reported in this frequency range. We compare data of the pumped I-V curves with the Wert- hamer-Tucker theory and demonstrate for the first time an excellent agreement at frequencies up to 500 GHz. For an array without integrated tuning stubs, a mixer noise tempe- rature T- = 90 f 30 K and a DSB mixer gain G-= -12.5 f 0.6 dB is measured. A comparison of the measured gain versus bias voltage with the quantum theory of mixing shows a good qualitative agreement, indicating the applicability of this theory, to Nb tunnel junctions up to 500 GHz. The noise temperature of an array with a lower gap voltage, is 220 K at 495 GHz. This frequency is 85 % of the reduced gap frequen- cy, indicating that Nb SIS mixers can be used up to at least the gap frequency of 680 GHz. I. INTRODUCTION

•Jan 1, 1993•0 citations
A receiver noise temperature of 61 K (DSB) has been measured for a superconductor–insulator–superconductor (SIS) heterodyne receiver operating at 232 GHz, the lowest value reported to date for such a receiver employing a lead alloy junction. Analysis of the losses of the receiver components yields mixer noise temperature and conversion loss, Tm = 24 K and Lm = 2.1 dB (DSB). These are compared with predictions based on 3-port quantum mixer theory, made using the measured characteristics of the junction and an equivalent circuit for the waveguide mixer mount deduced from scaled modelling experiments.
The development of ultra-low-noise receivers at frequencies of >200 GHz is primarily driven by astronomical applications. The most sensitive millimeter-wave receivers that have presently been constructed make use of the strong mixing afforded by superconductor-insulator-superconductor (SIS) tunnel junctions. In a collaborative project between UKC and RAL, a 230 GHz laboratory receiver has been built using a lead alloy SIS junction as the mixing element, mounted in 4:1 reduced-height waveguide, terminated at one end with a circular cross-section, adjustable backshort. Best results indicate a double-sideband receiver noise temperature of T/sub R/(DSB) approximately=120 K, which represents state-of-the-art performance at this frequency. Initial difficulties in achieving good mixing performance prompted an investigation into the importance of the 'quality' of mixer block backshort tuning elements. An analysis of the mixer equivalent circuit is presented which allows for loss in a non-ideal mixer block, and 3-port mixer model calculations are discussed which incorporate this analysis into the Tucker quantum theory of mixing.
The noise and gain of a heterodyne waveguide mixer using Nb/Al/sub 2/O/sub 3//Nb superconducting tunnel junctions were measured in the 400-500-GHz frequency range. Three different arrays of two junctions in series are analyzed. The minimum receiver noise temperature is 120 K DSB at 480 GHz, measured with an array having integrated tuning stubs. The authors compare data of the pumped I-V curves with the Werthammer-Tucker theory and demonstrate an excellent agreement at frequencies up to 500 GHz. For an array without integrated tuning stubs. a mixer noise temperature of 90+or-30 K and a DSB mixer gain of -12.5+or-0.6 dB were measured. A comparison of the measured gain versus bias voltage with the quantum theory of mixing shows good qualitative agreement, indicating the applicability of this theory to Nb tunnel junctions up to 500 GHz. The noise temperature of an array with a lower gap voltage is 220 K at 495 GHz. This frequency is 85% of the reduced gap frequency, indicating that Nb superconductor insulator-superconductor (SIS) mixers can be used up at least the gap frequency of 680 GHz.>
The authors have made a detailed study of the gain and noise of a SIS (superconductor-insulator-superconductor) heterodyne receiver at 345 GHz. An array of two Nb-Al/sub 2/O/sub 3/-Nb SIS junctions in series are used as the mixing element. The array is operated in a waveguide mount with a backshort and an E-plane tuner. The best receiver noise temperature achieved is 140 K DSB (double sideband). The embedding impedances were determined by fitting theory to the measured pumped curves. High-quality fits were obtained, providing the first detailed test of the Tucker-theory at frequencies above 300 GHz. The impedances found by this method are in very good agreement with impedances measured in a scale model at 3.3 GHz. From these embedding impedances, the gain and noise of the mixer were calculated over a full bias range using the Tucker theory in the three-port low-IF approximation. The measured dependence of mixer gain and noise on bias voltage, pump power and embedding impedance is in good agreement with theory. However the absolute values show discrepancies that appear to be independent of the bias parameters of the mixer.>
Experiments on the performance of superconductor-insulator-superconductor (SIS) tunnel junctions as heterodyne mixers at 40 GHz are reported. The techniques developed for the fabrication of multi-junction SIS series arrays differ from, and are considerably simpler than, other methods described in the literature. Results are reported on mixer noise temperature, conversion loss, saturation, local oscillator power levels and mixer dynamic range. Factors affecting the mixer's conversion performance are identified and comparisons are made with other reported results. It is concluded that mixer performance in the present experiments is limited by imperfect impedance matching at the signal frequency, due to relatively large values of parasitic capacitance in the junctions. Future work is aimed at both reducing the junction capacitance and redesigning the mixer mount to give improved r.f. matching.
The most sensitive heterodyne receivers used formillimeter wave and submillimeter wave radioastronomyemploy superconductor-insulator-superconductor (SIS)tunnel junctions as the nonlinear mixing element. Goodperformance has recently been reported for SIS junctionsused in planar mixer circuits and waveguide mixers fromabout 300 GHz to 500 GHz. We have developed asubmillimeter wave SIS heterodyne receiver for observingimportant rotational transitions of molecules in theinterstellar medium near 550 GHz and 630 GHz. Thisreceiver is based on a waveguide mixer with an adjustablebackshort and E-plane tuner [1]. The mixer uses a highcurrent density, 0.25 gm2 Nb-A1Ox-Nb tunnel junctiondefined by electron beam lithography [2]. The capacitanceof the junction is compensated with an integrated RFsuperconductive microstrip tuning circuit. The receiverperformance has been measured over the frequency range460 GHz to 640 GHz. DSB receiver noise temperatures aslow as 200 ± 17 K at 540 GHz and 362 ± 33 K at626 GHz have been obtained. In addition, negativedifferential resistance has been observed in the DC I-Vcurve at frequencies around 491 GHz. These results indicatethat the superconductive Nb microstrip transmission linesused in the tuning circuits are low-loss and perform well upto at least 90% of the superconductor energy gap frequency.
The noise and gain of a heterodyne waveguide mixer employing Nb/A120JNb superconducting tunnel junc- tions is measured in the 400-500 GHz frequency range. Three different arrays of two junctions in series are analyzed. An array with integrated tuning stubs has lowest receiver noise temperatures of T, = 120 K DSB at 480 GHz, which is to our knowledge the lowest value reported in this frequency range. We compare data of the pumped I-V curves with the Wert- hamer-Tucker theory and demonstrate for the first time an excellent agreement at frequencies up to 500 GHz. For an array without integrated tuning stubs, a mixer noise tempe- rature T- = 90 f 30 K and a DSB mixer gain G-= -12.5 f 0.6 dB is measured. A comparison of the measured gain versus bias voltage with the quantum theory of mixing shows a good qualitative agreement, indicating the applicability of this theory, to Nb tunnel junctions up to 500 GHz. The noise temperature of an array with a lower gap voltage, is 220 K at 495 GHz. This frequency is 85 % of the reduced gap frequen- cy, indicating that Nb SIS mixers can be used up to at least the gap frequency of 680 GHz. I. INTRODUCTION