Abstract
We report on research in the field of low-noise receiving systems in the sub-terahertz (THz) range, carried out in recent years, aimed at developing receivers with quantum sensitivity for implementation in space and ground-based radio telescopes. Superconductor-Insulator-Superconductor (SIS) mixers based on high-quality tunnel junctions are the key elements of the most sensitive sub-THz heterodyne receivers. Motivations and physical background for technology improvement and optimization, as well as fabrication details, are described. This article presents the results of the SIS receiver developments for the 211–275 GHz and 790–950 GHz frequency ranges with a noise temperature in the double sideband (DSB) mode of approximTELY 20 K and 200 K, respectively. These designs and achievements are implemented in the development of the receiving systems for the Russian Space Agency mission “Millimetron”, and for the ground-based APEX (Atacama Pathfinder EXperiment) telescope.
Highlights
The development of ultra-sensitive terahertz (THz) receivers is nowadays one of the most intensively and successfully explored areas of superconducting electronics [1,2].Superconducting elements offer an extremely high characteristic frequency and very strong nonlinearity
Many applications require a spectral resolution of ∆f/f~106 ; this can only be achieved with heterodyne receiving systems
A heterodyne receiver is sensitive to two input frequency bands, spaced on either side of the local oscillator (LO) frequency by the intermediate frequency (IF)—double sideband (DSB) mode
Summary
The development of ultra-sensitive terahertz (THz) receivers is nowadays one of the most intensively and successfully explored areas of superconducting electronics [1,2]. Superconducting elements offer an extremely high characteristic frequency and very strong nonlinearity This makes it possible to develop systems for receiving a THz signal with unique parameters unattainable for devices based on other principles. The mixers based on SIS tunnel junctions are the most developed input devices for heterodyne receivers at frequencies f from 0.1 to approximately 1.2 THz. The sharp nonlinearity in the tunneling current of the SIS junction is used for the mixer operation; this nonlinearity results from a single-electron tunneling process between two superconductors separated by a very thin oxide insulating layer. As an event horizon of a black hole is very compact, an extremely high angular resolution is required to observe details of these objects Such a resolution will be provided by the “Millimetron” orbit configuration in combination with ground-based telescopes [21]; the observatory will be located in the vicinity of the Lagrange point L2, at 1.5 million km from.
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