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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

LO path built-in SIS mixer for further improvement of noise performance

Kecheng Xiao, Hideo Ogawa, Akira Mizuno, Yasuo Fukui

Published Jul 3, 2000• 1 citation
Publisher

Abstract

In millimeter and submillimeter wave band, radio telescopes' observing efficiency and weak signal detecting capability have been greatly raised in the past tens of years, due to the application of the SIS mixers as their receiver front-ends. However general local power injection methods for a heterodyne receiver usually result in additional insertion loss which degrades sensitivity of SIS receivers. Based on the extremely small local power requirements of SIS quantum mixing, we developed a novel LO path built-in SIS mixer, in which an additional waveguide was built for LO power injection. Without any of traditional external LO diplexers (e.g., crossguide- couplers or beamsplitters), LO power is provided to SIS junctions through the LO waveguide and the junction chip which connects both LO- and signal waveguides. There is no RF signal lost due to coupling LO power since LO- and RF signal take different paths before arriving at junctions, resulting in a compact, stable and lower loss SIS receiver system. Experiments at 110- and 230 GHz bands show that there is no any problem to couple sufficient pumping power to SIS junctions from general LO sources for present LPB mixer, and the receiver sensitivities have a further improvement of about 10 K compared to our previous beamsplitter LO power coupling receiver system. We expect this LPB SIS mixer can be also applied into submillimeter wave band.

DOI
10.1117/12.390453

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In millimeter and submillimeter wave band, radio telescopes' observing efficiency and weak signal detecting capability have been greatly raised in the past tens of years, due to the application of the SIS mixers as their receiver front-ends. However general local power injection methods for a heterodyne receiver usually result in additional insertion loss which degrades sensitivity of SIS receivers. Based on the extremely small local power requirements of SIS quantum mixing, we developed a novel LO path built-in SIS mixer, in which an additional waveguide was built for LO power injection. Without any of traditional external LO diplexers (e.g., crossguide- couplers or beamsplitters), LO power is provided to SIS junctions through the LO waveguide and the junction chip which connects both LO- and signal waveguides. There is no RF signal lost due to coupling LO power since LO- and RF signal take different paths before arriving at junctions, resulting in a compact, stable and lower loss SIS receiver system. Experiments at 110- and 230 GHz bands show that there is no any problem to couple sufficient pumping power to SIS junctions from general LO sources for present LPB mixer, and the receiver sensitivities have a further improvement of about 10 K compared to our previous beamsplitter LO power coupling receiver system. We expect this LPB SIS mixer can be also applied into submillimeter wave band.
We have successfully demonstrated low-noise and wideband SIS mixers for the 275-500-GHz radio-frequency (RF) band, aiming to cover Atacama Large Millimeter/submillimeter Array band 7 (275-373 GHz) and band 8 (385-500 GHz) simultaneously. The waveguide SIS mixers integrate a multisection impedance transformer with a parallel-connected-twin-junction or single-junction circuits based on Nb/AlN/Nb trilayers with a critical current density of 31 kA/cm2. In order to achieve the targeted broadband performance, we designed an asymmetric one-side waveguide probe placed across a reduced height waveguide with dimensions 100 μm × 580 μm. The shape of the waveguide probe was optimized to have nearly constant impedance at around 35 Ω in the desired RF range. For evaluation of the receiver performance, we have established a dual-band noise temperature measurement system. The system implements a broadband corrugated horn antenna and a 15-dB RF/local oscillator (LO) waveguide coupler based on WR-2.3 (290 μm × 580 μm) waveguide size. The target bandwidth is too wide for typical LO sources at these high frequencies, and, therefore, we applied a dual-band LO injection system utilizing two different LO sources and an LO diplexer. The IF chain uses a cryogenic isolator and a low-noise amplifier with a typical noise temperature of 2.1 K over the 4-8-GHz range. The measured double sideband receiver noise temperature is two to three times the quantum noise at all LO frequencies for both the twin-junction and the single-junction circuits.
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.
Abstract We developed a low-noise, compact, balanced superconductor–insulator–superconductor (SIS) mixer, operating in the 787–950 GHz radio frequency range. A waveguide mixer block was designed to integrate all the key components, such as a radio frequency (RF) 90° hybrid coupler, two identical SIS mixer chips, bias-tees, and an intermediate frequency power-combiner. The RF waveguide 90° hybrid coupler consists of branch lines with wide slots optimized by numerical simulation, for ease of fabrication. The balanced mixer was installed into a cartridge type receiver, originally developed for the Atacama Large Millimeter/submillimeter Array Band 10 (787–950 GHz). The receiver demonstrated double sideband noise temperatures of approximately 200 K for most of the band, without any correction for loss in front of the receiver. The local oscillator noise rejection ratio was estimated to be more than 15 dB within the measured frequency range.
Heterodyne mixers based on superconducting SIS (superconductor-insulator-superconductor) tunnel junctions have been demonstrated to be the most sensitive coherent detectors at millimeter and submillimeter wavelengths. In fact, conventional superconducting SIS mixers with Nb/AlOx/Nb junction and Nb/SiO2/Nb tuning circuit have shown good performances with the noise temperature reaching as low as three times the quantum limit below 0.7THz, which is the gap frequency of Nb-based SIS junctions. However, due to the large loss in Nb thin-film superconducting microstrip lines, the noise performance of Nb SIS mixers deteriorates significantly above 0.7THz. With a gap frequency double that of Nb-based SIS junctions, NbN-based SIS junctions are of particular interest for the development of heterodyne mixers in the terahertz region. Considering the bandwidth and output power of local-oscillator (LO) signal sources are quite limited around 1THz, we firstly develop a waveguide NbN-based SIS mixer at 0.5THz. Three types of SIS junctions, i.e., long junction, parallel-connected tunnel junction (PCTJ) and distributed junction array (DJ) are investigated. They are all comprised of NbN-AlN-NbN tri-layer fabricated on an MgO substrate and have the same current density (Jc) of 10kA/cm2. In this paper, we describe their design, fabrication and preliminary experimental results.
The Atacama Pathfinder EXperiment (APEX) is a 12 m antenna operating at the Atacama Desert on the Chilean Andes at about 5000 m altitude. APEX would be equipped with a suit of single-pixel heterodyne receivers covering 211 - 1500 GHz frequency range. We present here a design of a sideband-separating superconductor-insulator-superconductor (SIS) mixer for the APEX, receiver Band 3, operating in 385 - 500 GHz band. The receiver uses quadrature scheme with the RF signal passing via a 90-degree waveguide 3 dB hybrid and the LO is divided by a waveguide E-plane Y-junction. The outputs of the waveguide hybrid are coupled to the mixer SIS junctions through an E-probe with integrated bias-T. For the LO coupler, conventional branch waveguide couplers are difficult to manufacture at this high frequency with required accuracy as the branch waveguides become extremely narrow. In order to solve this problem, we propose an on-chip LO injection, where the LO coupler is integrated onto the mixer chip and fabricated together with the SIS junction and the tuning circuitry. The on-chip LO coupler is made of superconducting lines, which gives almost a lossless solution and provides fabrication accuracy better than 0.5 μm by using optical lithography only. Furthermore, the mixer design includes a novel component, an ellipse termination for the idle LO port, made of thin-film resistive material with sheet resistance equal to the transmission line characteristic impedance, which gives very broadband performance using extremely compact area.
We present the design and first experimental results of a 385-500 GHz fixed-tuned double sideband (DSB) receiver based on a superconductor-insulator-superconductor (SIS) junction mixer with on-chip LO injection circuitry. At high frequency, branch waveguide couplers are difficult to manufacture with required accuracy as the branches (slots) become extremely narrow. In order to solve this problem, we propose a coupler integrated onto the mixer chip and fabricated together with the SIS junction and the tuning circuitry. The on-chip LO directional coupler is made of superconducting lines with slot lines in the ground plane. Thus, the coupler is integrated into conventional SIS junction fabrication steps, benefiting from the processing accuracy better than 0.5 μm by using optical lithography only. Furthermore, the mixer design includes a novel component, an ellipse termination for the idle LO port, made of thin-film resistive material. This termination gives very broadband performance using a compact area. Moreover, it is very tolerant to the sheet resistivity of the film, geometry and does not require any physical grounding [1]. The mixer is to be used at the Atacama Pathfinder EXperiment (APEX) telescope in Chile [2].