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IEEE Transactions on Magnetics

Harmonic mixing in a series array of short superconducting weak-links

Toshiaki Matsui, Bokuji Komiyama, Hiroshi Ohta

Published Mar 1, 1989• 3 citations
Publisher

Abstract

A new type of harmonic mixer using a series array of short superconducting weak-links is proposed for mixer applications at far-infrared and submillimeter-wave frequencies. The problem of limited mixer dynamic range can be eliminated by the use of a Josephson junction series array structure. Using a eleven-element series array, a preliminary experiment on harmonic mixing was carried out for two signals at 105.9 GHz and 5.4-12.6 GHz. IF (intermediate frequency) output was measured for each harmonic order from 9th to 19th by optimizing local power and bias voltage. In this experiment, 5-dB heightening of the signal-to-noise ratio was obtained at the IF output when the harmonic mixing order n was equal to the series element number, N=11.>

DOI
10.1109/20.92474

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A new type of harmonic mixer using a series array of short superconducting weak-links is proposed for mixer applications at far-infrared and submillimeter-wave frequencies. The problem of limited mixer dynamic range can be eliminated by the use of a Josephson junction series array structure. Using a eleven-element series array, a preliminary experiment on harmonic mixing was carried out for two signals at 105.9 GHz and 5.4-12.6 GHz. IF (intermediate frequency) output was measured for each harmonic order from 9th to 19th by optimizing local power and bias voltage. In this experiment, 5-dB heightening of the signal-to-noise ratio was obtained at the IF output when the harmonic mixing order n was equal to the series element number, N=11.>
When a signal at the nominal frequency of 76 GHz and a local oscillation (LO) at the frequency of a few gigahertz were both applied to a YBa2Cu3O7−y weak link immersed in liquid nitrogen, the former mixed with the harmonics of the latter giving rise to output at the intermediate frequency (IF) of about 150 MHz. The highest observed harmonic number was 51. Without exhaustive effort to optimize, the typical IF output power referred to the mixer output ranged between −103 and −112 dbm while the IF signal-to-noise ratio ranged between 16 and 4 db, depending strongly on the local oscillation power, the dc bias current, and the signal power. Reported in this letter are the experimental details as well as the requirements for a superconducting weak link to be a harmonic mixer.
Using a high Tc superconducting grain boundary Josephson junction, harmonic mixing experiments in the mm waveband were carried out, aiming at as large a harmonic number and as high a signal frequency as possible. The dependencies of intermediate frequency output on dc bias, harmonic number, frequency of local oscillator (LO), and other parameters were carefully studied. Until now, our best result was the mixing between the signal at 95 GHz and the 105th harmonic of LO at about 900 MHz. Preliminary experiments using a high Tc harmonic mixer and phase-locking loop were tried to stabilize the frequency of a mm wave source.
Using a superconducting weak link (bridge) made of YBCO, the authors have successfully observed Josephson harmonic mixing between a local oscillation (LO) at X band and a signal at Ka band. Specifically, fourth-order harmonic mixing between 35.47 GHz and 8.843 GHz was observed. For a given signal level, the IF (intermediate frequency) responses depended strongly on both LO level and DC voltage bias across the junction. For zero bias, there is still IF output which is characteristic of even-order harmonic mixing. When the LO power level is such that the zero voltage current is suppressed to the second zero, the IF responses are maximum if the junction is biased between the zeroth and first steps induced by the LO. Also studied is the internal oscillation-mixing. An incoming signal at either X or Ka band gives rise to IF signal peaks if the junction is biased at voltages such that the corresponding internal Josephson frequencies are equal to, or harmonics of, the incoming signal frequency.>
Two high-Tc superconducting (HTS) YBa2Cu3O7-δ(YBCO) grain boundary (GB) Josephson junctions in series as a harmonic mixer is investigated. The research shows that the mixer consisting of two series YBCO Josephson junctions has a larger harmonic number than that with only one junction in heterodyne mixing at zero-voltage bias. One of the advantages of the series-Josephson-junction mixer is that the total critical current is improved without sacrificing the sensitivity of the junctions in the array that makes the mixer easier to get more microwave induced-steps required by larger harmonic number. Furthermore, the underdamped YBCO GB series-Josephson-junction mixer operated at zero-bias voltage, where the zero-order Shapiro step exists, achieves mutual phase locking of the junctions in the array, resulting in an excellent mixing performance. Thus, the series-underdamp-Josephson-junction mixer with zero bias is predominant and compact in terahertz (THz) application due to its excellent performance and no dc bias supply.
The authors present a model for a series-parallel array of small metallic (nontunneling) Josephson junctions. The transmission and configuration of pair electrons between small superconducting regions are considered assuming the presence of a strong interaction between the electrostatic energy (2e)/sup 2//2C and the Josephson effect in a network of metallic weak links. The model predicts that the same behavior as that of a single junction is obtained with a superconducting weak-link device comprising multiple small superconducting regions joined by conductive bridges. In an experiment in the 100- and 320-GHz frequency ranges, the constriction of a YBCO film formed with a network of grain-boundary Josephson weak links showed that the AC Josephson effect is the same as for a single Josephson element. It is confirmed that the constriction works as a harmonic mixer at 318 GHz and that a network of high-T/sub c/ superconducting weak links can be used for a practical device operating at submillimeter-wave frequencies.>