Integrated tuning elements for millimeter and sub-millimeter SIS mixers

The authors present two different designs of integrated tuning elements for superconducting tunnel junction mixers. The structures consist of a self-complementary log-periodic antenna, superconductor-insulator-superconductor (SIS) tunnel junction, and a broadband superconducting tuning circuit placed between the center of the antenna and the SIS junction. The designs allow good coupling to relatively large-area (7 mu m/sup 2/) junctions. The best design has a 3-dB bandwidth of 102 GHz at the central frequency of 98 GHz, and 75 GHz at the central frequency of 492 GHz. Microwave scale-model measurements show excellent agreement with simulation results. Devices are being fabricated in niobium technology.<>