Abstract
We designed and tested a quasi-optical SIS mixer that incorporates a substrate lens for the 100 GHz band. The mixer uses a planar self-complementary log-periodic antenna with an integrated tuning circuit. The antenna has a frequency independent impedance of around over several octaves. The tuning circuit consists of two SIS junctions connected in parallel through a superconducting stripline inductor for tuning out the junction capacitances and a impedance transformer for matching the junction resistance to the antenna impedance. The SIS junctions are and have an area of and a current density of . The IF output from the mixer is brought out in a balanced way at each edge of the antenna, and is coupled to a cooled low-noise amplifier through a balun transformer by using a hybrid coupler. A double-sideband receiver noise temperature less than 130 K was measured from 85 to 110 GHz. The best noise temperature was 90 K at 101 GHz, which is the same as for waveguide receivers.
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