Investigation of Superconducting Quasiparticle Mixers for Astronomical Receivers

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Receivers based upon the superconductor-insulator-superconductor (SIS) quasiparticle tunnel junction mixer have now surpassed conventional Schottky-diode receivers in sensitivity, and are having an immediate impact on millimeter-wavelength astronomy. Even so, much further research is needed before this technology can reach its full potential. Therefore, an extensive experimental study of SIS junctions as millimeter-and submillimeter-wave detectors will be undertaken better analytical and intuitive understanding of SIS mixers and related phenomena, relying on the quantum theory of mixing, with special attention to noise phenomena, optimum mixer design parameters, tuning structures, will be sort, as will the appropriate capacitance for SIS junctions. Investigation of less widely accepted detection schemes, such as SIN mixers, subharmonic pumping, and SIS direct detection will be Experimentally studied. The Nb/AlO/Nb juctions made in laboratory, which have extraordinarily low leakage currents, will be utilized in this work. These junctions will be made available to the radio astronomy community for SIS receiver devleopment. This investigation should greatly contribute to the design and ultimate sensitivity of practical SIS receivers; and may lead to the development of other detectors for millimeter and submillimeter wavelength astronomy.