Abstract. Presently a Josephson Flux Flow Oscillator (FFO) appears to be the most developed superconducting on-chip local oscillator for integrated submm-wave SIS receivers.The feasibility of phase locking the FFO to an external reference oscillator at all frequencies of interest has to be proven for practical FFO implementation in radio astronomy and other spectral applications. A linewidth of a phase-locked FFO as low as 1 Hz has been measured relative to an external reference oscillator in the frequency range 270 -440 GHz on steep Fiske steps in the low damping regime. The increase of the intrinsic linewidth at higher voltages due to an abrupt increase of the internal damping considerably complicates phase locking of the FFO.Comprehensive measurements of the FFO radiation linewidth have been performed using an integrated harmonic SIS mixer. Results on FFO linewidth and spectral line profile have been compared to theory in order to optimize the FFO design. The influence of FFO parameters on radiation linewidth, particularly the effect of the differential resistances associated both with the bias current and the applied magnetic field, has been studied. Two integrated receiver concepts with phase-lock loop have been developed and experimentally tested.

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A Josephson Flux Flow Oscillator (FFO) is the most developed superconducting local oscillator for integration with an SIS mixer in a single-chip submm-wave receiver. Recently, using a new FFO design, a free-running linewidth 10 MHz has been measured in the frequency range up to 712 GHz, limited only by the gap frequency of Nb. This enabled us to phase lock the FFO in the frequency range 500-712 GHz where continuous frequency tuning is possible; resulting in an absolute FFO phase noise as low as 80 dBc at 707 GHz. Comprehensive measurements of the FFO radiation linewidth have been performed using an integrated SIS harmonic mixer. The influence of FFO parameters on radiation linewidth, particularly the effect of the differential resistances associated both with the bias current and the applied magnetic field has been studied in order to further optimize the FFO design. A new approach with a self-shielded FFO has been developed and experimentally tested.

A submillimeter spectrometer for measurements of low concentrations in gas mixtures is developed and created. The radiation source is a 260–380 GHz backward wave oscillator (BWO). The BWO frequency is stabilized by means of a reference microwave channel, incorporating a cell with a gas under test the spectral line of which is used as frequency discriminator. Fast frequency scanning in the vicinity of the spectral line is used to reduce the effects of acoustic noise and vibrations and to upgrade time resolution. The background’s signals due to interference in the measuring cell of the spectrometer are suppressed by using a original nonstationary modulation method. Theoretical analysis of that method has been carried out. A description of the design and analysis of possible applications for the spectrometer, as well as the results of some experimental studies supported by the spectrometer are provided.