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

A 275- to 370-GHz SIS mixer for the APEX telescope

Christophe Risacher, Victor Y. Belitsky, Vessen Vassilev, Alexey Pavolotsky

Published Oct 8, 2004• 0 citations
Publisher

Abstract

Atacama Pathfinder EXperiment (APEX) submillimeter telescope is currently under completion on Chajnator, at an altitude of 5050 m on the Atacama Desert, in the Northern Chile. The telescope facility heterodyne receivers should have 3 bands covering 211-500 GHz. We present design of a 275-370 GHz SIS mixer to be used as a first light APEX Band 2 receiver. A novel waveguide-to-microstrip transition with integrated bias-T is used in this mixer. This structure allows coupling of the RF signal from a full height waveguide to a thin-film superconducting line via E-probe. The wide side of the probe is connected to another port via a specially shaped high impedance line that provides RF/DC isolation. This port is used to extract the IF signal and to inject a DC current that creates a local magnetic field parallel to the plane of the SIS junction to suppress the Josephson effect. The main advantage of this type of Josephson suppression circuit is its compactness as it uses the existing superconducting lines from the SIS integrated tuning circuitry. The entire structure with the probe, SIS junction with its tuning circuitry is placed on a quartz substrate. For more advanced designs, as a sideband separating or balanced mixer that we intend to have for the final version of the APEX telescope heterodyne receiver, the SIS junctions of two balanced or quadrature mixers will be at a very close distance. The standard solution of using superconducting coils to suppress Josephson effect is very difficult to implement and, therefore, this new structure should be of a great advantage.

DOI
10.1117/12.550333

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IEEE Microwave and Wireless Components Letters•Jan 1, 2008•22 citations
Atacama Pathfinder EXperiment (APEX) submillimeter telescope is currently under completion on Chajnator, at an altitude of 5050 m on the Atacama Desert, in the Northern Chile. The telescope facility heterodyne receivers should have 3 bands covering 211-500 GHz. We present design of a 275-370 GHz SIS mixer to be used as a first light APEX Band 2 receiver. A novel waveguide-to-microstrip transition with integrated bias-T is used in this mixer. This structure allows coupling of the RF signal from a full height waveguide to a thin-film superconducting line via E-probe. The wide side of the probe is connected to another port via a specially shaped high impedance line that provides RF/DC isolation. This port is used to extract the IF signal and to inject a DC current that creates a local magnetic field parallel to the plane of the SIS junction to suppress the Josephson effect. The main advantage of this type of Josephson suppression circuit is its compactness as it uses the existing superconducting lines from the SIS integrated tuning circuitry. The entire structure with the probe, SIS junction with its tuning circuitry is placed on a quartz substrate. For more advanced designs, as a sideband separating or balanced mixer that we intend to have for the final version of the APEX telescope heterodyne receiver, the SIS junctions of two balanced or quadrature mixers will be at a very close distance. The standard solution of using superconducting coils to suppress Josephson effect is very difficult to implement and, therefore, this new structure should be of a great advantage.
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.
Abstract — We present the design and the experimental results of a fixed-tuned sideband-separating superconductor-insulator-superconductor (SIS) mixer for 385- 500 GHz. The sideband separation is achieved using a quadrature scheme, where two separate DSB mixer blocks are combined with an intermediate waveguide component containing the LO waveguide distribution circuitry and RF waveguide hybrid. The intermediate waveguide piece is fabricated by using copper micromachining, which gives dimensions ’ accuracy better than 1 μm. The RF signal coming from the waveguide hybrid is coupled to the SIS junctions through an E-probe with integrated bias-T. We implemented an on-chip LO injection solution, 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 as a combination of superconducting microstrip lines and slot-lines (branches), which gives almost a lossless solution. With the fabrication accuracy better than 0.5 μm by using optical lithography, the circuitry is proven to give a good performance following the simulations expectations. I.
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].
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.
In this paper, we report about the development, fabrication, and characterization of a balanced waveguide hot electron bolometer (HEB) receiver for the Atacama Pathfinder EXperiment telescope covering the frequency band of 1.25–1.39 THz. The receiver uses a quadrature balanced scheme and two HEB mixers, fabricated from 4- to 5-nm-thick NbN film deposited on crystalline quartz substrate with an MgO buffer layer in between. We employed a novel micromachining method to produce all-metal waveguide parts at submicrometer accuracy (the main-mode waveguide dimensions are 90$\,\times\,180180180\mu{\hbox{m}}$). We present details on the mixer design and measurement results, including receiver noise performance, stability and “first-light” at the telescope site. The receiver yields a double-sideband noise temperature averaged over the RF band below 1200 K, and outstanding stability with a spectroscopic Allan time more than 200 s.
We present the final results of the development and characterization of the sideband separating superconductor-insulator-superconductor (SIS) mixer for the APEX telescope band 1 (211-275 GHz). The sideband separation is achieved by using a quadrature scheme where the radio frequency (RF) and a local oscillator (LO) power are applied to two identical double sideband SIS mixers. All mixer components, including the LO and RF distribution circuitry, are integrated into a single mixer block. To achieve a compact design we developed a superconducting Lange coupler, based on Nb thin film, which is used as an intermediate frequency hybrid. Typical single sideband noise temperature of 100 K and sideband rejection ratio of about 12 dB and are measured.