Development of a Waveguide Josephson Oscillator for SIS Mixer-Based Amplifiers

A waveguide Josephson array oscillator operating at a frequency of 100 GHz was designed and fabricated to evaluate its pumping capability as a local oscillator (LO) for our proposed SIS mixer-based amplifier, which incorporates SIS up- and down-converters. The LO power requirement was estimated by simulation to be several nanowatts when the SIS up-converter is optimized for noise temperature and conversion gain under the condition that the input port at the microwave frequencies is connected to a practical 50-Ω system. The fabricated waveguide Josephson array oscillator module has 31 Nb Josephson junctions placed at the center of a half-wavelength resonator of an Nb microstripline. The output power from the waveguide oscillator module was evaluated by connecting it to the waveguide SIS detector module in a 4-K cryostat. Photon-assisted tunneling steps were clearly observed, from which the detected power was estimated to be approximately 17 nW at 106 GHz. These results suggest that the Josephson array oscillator is capable of being used in the SIS mixer-based amplifier as the LO.