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IEEE Transactions on Applied Superconductivity

A 650 GHz fixed-tuned waveguide SIS distributed mixer with no integrated tuning circuit

Edward Tong, R. Blundell, Koko G. Megerian, J. A. Stern, Henry George LeDuc

Published Jun 1, 2003• 8 citations
Publisher

Abstract

A Superconductor-Insulator-Superconductor (SIS) distributed mixer with no integrated tuning circuit has been designed for use in a fixed-tuned waveguide mixer block. This mixer employs two half-wave SIS resonators connected in series across the feed point of the waveguide circuit. By selecting appropriate dimensions for the resonators, we can obtain proper impedance matching over a reasonable input bandwidth. Since there is no lossy thin film microstrip line in front of the SIS junction, efficient power transfer from the waveguide feed to the mixer element can be achieved. A receiver noise temperature of 185 K at 650 GHz has been measured with a dual 0.33/spl times/16.8 /spl mu/m SIS resonator. The noise temperature remains below 300 K over an input bandwidth of about 10%. This design can be used at much higher frequency where the loss of tuning circuit becomes significant.

DOI
10.1109/tasc.2003.813996

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IEEE Transactions on Applied Superconductivity•Jun 1, 2003•6 citations
A Superconductor-Insulator-Superconductor (SIS) distributed mixer with no integrated tuning circuit has been designed for use in a fixed-tuned waveguide mixer block. This mixer employs two half-wave SIS resonators connected in series across the feed point of the waveguide circuit. By selecting appropriate dimensions for the resonators, we can obtain proper impedance matching over a reasonable input bandwidth. Since there is no lossy thin film microstrip line in front of the SIS junction, efficient power transfer from the waveguide feed to the mixer element can be achieved. A receiver noise temperature of 185 K at 650 GHz has been measured with a dual 0.33/spl times/16.8 /spl mu/m SIS resonator. The noise temperature remains below 300 K over an input bandwidth of about 10%. This design can be used at much higher frequency where the loss of tuning circuit becomes significant.
The non-linear quasiparticle tunnel current flowing in a distributed superconductor-insulator-superconductor (SIS) transmission line resonator has been exploited in a low-noise heterodyne fixed-tuned waveguide receiver in the 600-720 GHz band. The mixer employs two 1.4 /spl mu/m wide half-wave or full-wave distributed SIS long junctions that are connected in series. These devices have been fabricated with optical lithography. Noise temperatures of 160-240 K have been measured at around 600 GHz. However, the achieved RF bandwidth is only about 5 % and the center frequency of the resonance is also shifted towards lower end of the target frequencies.
A fixed-tuned SIS(Superconductor-Insulator-Superconductor) mixer across 120∼180 GHz band has been developed. This mixer employs an SIS chip fabricated by Nobeyama radio observatory which consists of a series array of 6 Nb/Al-AlO/Nb junctions in a microstrip line on a fused quartz substrate. The SIS chip is placed at the center of the half-height waveguide mixer mount to have a good incoming signal coupling over the whole frequency band. No mechanical tuner was used in the SIS mixer and the RF signal and local oscillator power are injected to the mixer via a cooled cross-guide coupler. In order to prevent the IF signal loss, the If output impedance of the SIS mixer was matched to the 50 input impedance of the IF chain. Measured double sideband noise temperatures of a receiver using the SIS mixer are 32∼131 K over 120∼180 GHz band. The developed SIS mixer is now in use for radio astronomical observations on the TRAO 14 m radio telescope.
This paper presents design and performance data for a 100-GHz waveguide superconductor-insulator-superconductor (SIS) mixer, which is incorporated with a twin-junction device (i.e., two identical junctions connected in parallel through a tuning inductance) and a fixed-tuned broad-band waveguide mixer mount. The 100-GHz mixer is actually developed as a prototype of the 500-GHz one. The constructed 100-GHz SIS receiver results in an overall receiver noise temperature (DSB) of less than 40 K over the frequency range from 80-120 GHz, with a minimum value of just 20 K that is four times as large as the quantum limit (i.e., 4/spl planck//spl omega//k). Such a performance is comparable or even superior to those of the best mechanically tunable waveguide SIS receivers at the same frequency band. In addition, some interesting mixing behaviors related to this two-junction device are described in detail.
A circuit that produces broadband impedance matching with low-current-density junctions at submillimeter wavelengths for tuning superconductor–insulator–superconductor (SIS) mixers is described; it consists of half-wavelength distributed SIS junctions connected alternately by half-wavelength microstrip lines. It is made of Nb and was designed for two practical source impedances using numerical calculation based on the Mattis–Bardeen theory of the anomalous skin effect at 660 GHz, assuming SIS junctions with a current density of 5 kA/cm 2 . An SIS mixer tuned using this circuit had a large fractional bandwidth of more than 18%, below -10 dB matching, even though the assumed ω C J R N product was about 16. Investigation of the mixer performance using Tucker's quantum theory of mixing showed that it has excellent broadband and low-noise characteristics compared with conventional mixers consisting of half- or full-wavelength distributed elements.
We present a novel superconducting waveguide mixer for 800 GHz. In this mixer, a half-wave Nb/Al-AlO/sub x//Nb superconducting-insulator-superconductor (SIS) resonator is integrated with a microstrip superconducting transmission line loaded with coplanar inductors. This hybrid coplanar/microstrip transmission line acts as an impedance matching section between the distributed junction and the waveguide feed point of the mixer mount. We have designed mixers with a simple model which predicts that the insertion loss of the matching network is less than 10 percent up to 840 GHz. Preliminary experimental results show that the resonator can work up to 800 GHz but the parameters of the coplanar inductor loaded microstrip line need to be refined to improve power coupling to the resonator.
We have designed and fabricated waveguide superconductor-insulator-superconductor (SIS) receivers at 870 GHz with NbN/AlN/NbN tunnel junctions on an MgO substrate. A waveguide probe was incorporated into the mixer chip for a waveguide-to-microstrip transition. As the tuning circuit for the SIS mixer, we designed a resonant distributed junction whose length is one wavelength and critical current density is 20 kA/cm/sup 2/. The mixing properties were calculated based on the quantum theory of mixing. The SSB mixer noise temperature should be less than 100 K and conversion gain larger than -8.0 dB in the frequency range from 840 to 920 GHz. We also observed the resonance steps of the fabricated SIS mixer. The tuning frequency was slightly higher than the designed frequency.