A W-band SIS mixer employing PCTJ (Parallel-Connected Twin Junctions)

Abstract

SIS (Superconductor-Insulator-Superconductor) junctions of a large omegaR(sub n)C(sub j) product (e.g., greater than 4), which may lead to a low current density and a large junction area for easy fabrication, have been widely adopted for millimeter- and submillimeter-wave mixers. As such a large omegaR(sub n)C(sub j) product definitely costs the performance of the SIS mixer, the parallel-connected twin junctions (separated by a tuning inductance) were used for the W-band SIS mixer. In comparison to other tuning circuits reported to date, it has a broader tuning bandwidth, easier RF (Radio Frequency) impedance matching, and possibly easier for fabrication. Since this W-band SIS mixer is expected to be scaled down to submillimeter wavelengths, a fixed-tuned broadband SIS mixer mount incorporating a novel waveguide-to-suspended stripline transition has been developed. The constructed W-band SIS mixer has demonstrated an excellent performance, giving a DSB (Double Sideband) receiver noise temperature of less than 40 K in the frequency range from 80 to 120 GHz and a minimum value of about 20 K that is just 4h(nu)/k.

たとえば4以上のようにωR(sub n)C(sub j)積が大きいSIS(超伝導体-絶縁体-超伝導体)接合はミリ波およびサブミリ波ミクサにかなり採用されている。この接合は、容易な製造で低い電流密度と大きな接合面積が得られる場合がある。このような大きなωR(sub n)C(sub j)積は確実にSISミクサの性能を失わせるので、並列接続2接合(同調インダクタンスで分離)をW波帯SISミクサに用いた。最近報告された他の同調回路と比較して、このミクサは同調帯域幅が広く、RF(高周波)インピーダンス整合が簡単で、製造がかなり容易である。このW波帯SISミクサをサブミリ波帯で使用することが期待されているので、新しい導波路-サスペンデッドストリップ線路遷移を組込んだ固定同調型広帯域SISミクサマウントを開発した。構成したW帯SISミクサはDSB(両側波帯)が80-120GHzの周波数域でDSB受信機雑音温度が40Kより低く、最低値は約20K、すなわち、ちょうど4hν/kという優れた性能を示した。