Resonant Cherenkov radiation in Josephson flux flow oscillators with integrated meander-shaped transmission line

Abstract

A novel Cherenkov flux flow oscillator (CFFO) is considered. The system consists of a long Josephson junction with an overlaying meander-shaped stripline. The traveling wave in the line is exited at each intersection point by the chain of fluxons moving along the junction. At certain resonance frequencies the radiation delivered to the stripline from all intersections points interfere constructively and the generated power reaches its maximum value. To first order the resonance condition is given by the distance between the fluxons, and is independent of the system boundaries. So one can change the resonance frequency by varying the external magnetic field. This is radically different from oscillators relying on conventional internal junction resonances such as the Fiske resonance, and allows for design of a powerful CFFO which can be electronically tuned. The existence of resonant interactions with both forward and backward waves is shown, and the analogy to the Cherenkov synchronism is demonstrated. Numerical simulations confirm the analytical predictions and allow us to investigate the strongly nonlinear case. The proposed CFFO is ideally suited for realization in HTSC technology.