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Journal of Physics Conference Series

An SIS-based sideband-separating heterodyne mixer optimized for the 600 to 720 GHz band

Fausto Patricio Mena, J. Kooi, Andrey M. Baryshev, C. F. J. Lodewijk, Ronald Hesper, W. Wild, T. M. Klapwijk

Published Feb 1, 2008• 3 citations

Abstract

The Atacama Large Millimeter Array (ALMA) is the largest radio astronomical enterprise ever proposed. When completed, each of its 64 constituting radio-telescopes will be able to hold 10 heterodyne receivers covering the spectroscopic windows allowed by the atmospheric transmission at the construction site, the altiplanos of the northern Chilean Andes. In contrast to the sideband-separating (2SB) receivers being developed at low frequencies, double-side-band (DSB) receivers are being developed for the highest two spectroscopic windows (bands 9 and 10). Despite of the well known advantages of 2SB mixers over their DSB counterparts, they have not been implemented at the highest-frequency bands as the involved dimensions for some of the radio frequency components are prohibitory small. However, the current state-of-the-art micromachining technology has proved that the structures necessary for this development are attainable. Here we report the design, modeling, realization, and characterization of a 2SB mixer for band 9 of ALMA (600 to 720 GHz). At the heart of the mixer, two superconductor-insulator-superconductor (SIS) junctions are used as mixing elements. The constructed instrument presents an excellent performance as shown by two important figures of merit: noise temperature of the system and side band ratio, both of them within ALMA specifications.

DOI: 10.1088/1742-6596/97/1/012331

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Abstract We have designed and mass-produced low-noise sideband separating superconductor–insulator–superconductor (SIS) mixers for the Atacama Large Millimeter/submillimeter Array (ALMA) band 4 over the frequency range of 125–163 GHz. An integrated design was adopted for the band 4 sideband separating (2SB) mixer block because of the advantages it offers in terms of compactness, reduced testing time and lower cost. The mixer chip was designed to be robust for handling errors to avoid performance degradation caused by generation of the higher order mode in the mixer chip slot. Detailed analyses revealed its robustness and ability to ensure mass production of the 2SB mixers. Using the robust mixer design in addition to well-established waveguide technologies, all of the 2SB mixers met ALMA specifications for noise temperature and image rejection ratio.

We have developed a Sideband Separating (2SB) Mixer based on superconductor-insulator-superconductor (SIS) junctions for frequency range 790-950 GHz. In the first test this mixer demonstrated the noise temperature from 450 to 900 K and the image rejection ratio above 15dB in 95% of the band. The SIS mixers used here have DSB noise temperature form 220 to 400 K. These results show that RF waveguide hybrid structure for such a high frequencies can be manufactured with losses level below 0.8 dB. It makes attractive possible ALMA upgrade of Band 10 receivers to 2SB option, because the sensitivity for spectral lines observations can be improved by about 30% by using 2SB mixers instead of DSB ones.

We present the design and preliminary experimental results of superconductor-insulator-superconductor (SIS) mixers for Atacama large millimeter array (ALMA) band 10 (780-950GHz) receivers. To achieve wide frequency coverage as well as low noise temperature, we integrated high current density (10 kA/cm2) and small-sized (one micrometer in diameter) Nb/AlOx/Nb SIS junctions with a tuning microstrip line using NbTiN ground plane and Al wiring layers. High quality NbTiN films with Tc reaching 14.5 K and Al films with residual resistivity ratio as large as 15 have been achieved. To minimize the waveguide transmission loss and facilitate the fabrication of mixer block, a full height waveguide was adopted. The waveguide probe was optimized to achieve low input impedance in the frequency range of 780-950 GHz while adopting a backshort cavity of zero depth. Preliminary RF testing with a Nb/Al microstrip tuning circuit demonstrated a DSB receiver noise temperature about 400 K at 832.5 GHz, which promises the accommodation of receiver performance in ALMA specification with low loss NbTiN/Al microstrip lines.

A total of 73 dual polarization superconductor-insulator-superconductor (SIS) receivers for the Atacama Large Millimeter/submillimeter Array (ALMA) have been successfully produced to observe astronomical signals in the 787-950 GHz frequency band. The receivers use two double sideband (DSB) waveguide mixers with Nb/AlOx/Nb tunnel junctions and NbTiN/SiO2/Al microstrip tuning circuits on quartz substrate. The best achieved DSB receiver noise temperature is 125 K, corresponding to about 3 hf/kBfor 4 K operation.