Microwave Amplification in SIS junctions with internal LO pump

S. V. Shitov, V. P. Koshelets, Andrey B. Ermakov +4 more

Experimental details of a unique superconducting imaging array receiver are discussed. Each pixel contains an internally pumped receiver chip mounted on the back of the elliptical microwave lens. Each chip comprises a quasi-optical SIS mixer integrated with a superconducting flux-flow oscillator (FFO) both fabricated from the same Nb/AlO/sub x//Nb trilayer on a silicon substrate. Properties of the integrated lens antenna were studied using an externally pumped reference SIS mixer which showed antenna sidelobes below /spl sim/17 dB and a receiver double side band noise temperature, T/sub RX/(DSB), below 100 K within the frequency range 460-500 GHz that is close to the quantum noise. For the imaging array T/sub RX/(DSB)=150 K has been measured at 500 GHz using the internal flux-flow oscillator as a local oscillator (LO). A balanced SIS mixer was tested showing T/sub RX/(DSB)<100 K within the range of 480-510 GHz using the internal LO. A computer system was developed to control simultaneously the dc bias of the SIS mixer and the frequency and power provided by FFO. The system also performs automatic optimization of the receiver noise temperature.

David Abergel

A.S. Clorfeine

Yoshinori Uzawa, Akira Kawakami, Takafumi Kojima +6 more

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-W 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.

Donald G. McDonald

A. D. Smith, R. A. Batchelor, William R. McGrath +4 more

We have demonstrated quasi particle harmonic mixing of a 36 GHz signal with an 18 GHz local oscillator in tin SIS junctions. Harmonic mixers can have important advantages at high microwave frequencies where insufficient LO power is available.