Radiation linewidth of f lux-f low oscillators

The results of linewidth measurements on flux-flow oscillators (FFOs) of a new design with improved parameters are presented. Extensive measurements of the dependence of the free-running FFO linewidth on the differential resistances associated both with the bias current and the control-line current (applied magnetic field) are taken. A profile of the FFO radiation line is measured in different regimes of FFO operation and compared to the theoretical models. A Lorentzian shape of the FFO line is observed both at Fiske steps (FSs) in the resonant regime and on the flux-flow step (FFS) at high voltages. A phenomenological model of the FFO linewidth taking into account all known noise sources (both internal and external) is used to explain the FFO linewidth dependence on the experimental parameters. Finally, we discuss the feasibility of using an electronic phase-locking loop (PLL) over the entire FFO operational frequency band.