A superconducting phase-locked local oscillator for a submillimetre integratedreceiver

Abstract

Comprehensive measurements of the flux flow oscillator (FFO) radiation linewidthare performed using an integrated harmonic SIS mixer; the FFO linewidth andspectral line profile are compared to a theory. An essential dependence of the FFOlinewidth on frequency is found; a possible explanation is proposed. The results of thenumerical solution of the perturbed sine–Gordon equation qualitatively confirm thisassumption. To optimize the FFO design, the influence of the FFO parameters on theradiation linewidth is studied. A novel FFO design at a moderate current density hasresulted in a free-running FFO linewidth of about 10 MHz in the flux flow regimeup to 712 GHz, limited only by the gap frequency of Nb. This relatively narrowfree-running linewidth (along with implementation of a wide-band phase locking loopsystem) allows continuous phase locking of the FFO in the wide frequency range of500–710 GHz. These results are the basis for the development of a 550–650 GHz integratedreceiver for the terahertz limb sounder (TELIS) intended for atmosphere study andscheduled to fly on a balloon in 2005. We report here also on the design of the secondgeneration of the phase-locked superconducting integrated receiver chip for TELIS.