Superconductor-Insulator-Superconductor (SIS) mixers are currently the most widely used detectors in astronomical observations in the terahertz band. To meet the demands of future large-aperture terahertz radio telescopes for multipixel applications, this work focused on the integration technology of a 660 GHz 1×4 one-dimensional linear array SIS mixers. The SIS mixers based on Nb/AlN/NbN twin tunnel junctions. We developed the uniform distribution of local oscillator power by using an integrated waveguide and multi-path local oscillator power distribution network. We also integrated the passive frequency doubler and tripler at low temperature, and integrated four low-noise amplifiers with the mixer in the same block, resulting in a more compact structure. As a result, we successfully realized the simultaneous operation of four mixers in a cryogenic Dewar. This paper will provide a detailed description of the relevant design and testing results.
The Leighton Chajnantor Telescope (LCT) project, sponsored by Shanghai Normal University in collaboration with Caltech and the University of Concepción, is seeking to relocate the Caltech Submillimeter Observatory (CSO)[1] from Mauna Kea, Hawaii to Llano de Chajnantor Observatory on the Chajnantor Plateau in Chile. The LCT will be equipped with a new 345-GHz band heterodyne array receiver of 3×3 beams and quantum-limited sensitivity. Based on superconducting Nb/Al-AlOx/Nb tunnel junction (SIS) mixers, we have developed a compact 1×3 array as one unit of the new heterodyne array receiver. Detailed design and measurement results will be presented.
Superconductor–insulator–superconductor (SIS) mixers remain the choice of heterodyne mixers for single-dish telescopes and interferometers at millimeter and submillimeter wavelengths. Compared with conventional Nb/AlOx/Nb superconducting tunnel junctions, Nb/AlN/NbN ones have larger gap voltage and may reach critical-current density beyond 10kA/cm2, which are both of particularly interest in developing broadband SIS mixers. Here we report on the design and measurement of an SIS mixer based on Nb/AlN/NbN parallel connected twin junctions (PCTJ) incorporating NbTiN/SiO2/Al microstrip circuit. The junctions have a gap voltage of 3.18mV and a critical-current density of 15kA/cm2. The measured receiver noise temperature reach 5hν/kB among 200-260GHz band, and the mixer’s fractional bandwidth is about 40% centered at 230GHz.
Besides the sensitivity nearly approaching the quantum limit, the intermediate-frequency (IF) bandwidth is of particular interesting for Superconductor-insulator-superconductor (SIS) mixers for radio astronomy research. In this paper, we are going to present the characteristic of IF bandwidth of two type of NbN SIS mixers, Long distributed junctions and Parallel-connected twin junctions. Firstly, the relative mixer gain are measured with different IF load impedance (25Ω, 50Ω, 75Ω) for both two SIS mixers. And also the mixers gain with different IF load impedance is simulated to get the optimum IF load impedance over a relative large IF bandwidth (2-15GHz). Finally, an IF matching circuit is designed and measured associating with SIS mixers, the measurement results show that the mixers gain are flatter over a large IF bandwidth than with 50Ω IF load impedance.
Superconductor-insulator-superconductor (SIS) mixers, with nearly quantum-limited sensitivity, have been playing an important role in Terahertz astronomy. For practical THz SIS receivers, however, the measured noise temperatures are sometimes higher than the expected value. The extra noise is mainly due to considerable RF noise contribution from the receiver components such as beam splitter, Dewar window, and infrared filter. In this paper, we mainly present the simulation and measurement results of the three components with different materials and thicknesses. Their noise contributions are also analyzed.
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