A millimeter wave relativistic backward wave oscillator operating in TM03 mode with low guiding magnetic field

Abstract

A V-band overmoded relativistic backward wave oscillator (RBWO) guided by low magnetic field and operating on a TM03 mode is presented to increase both the power handling capacity and the wave-beam interaction conversion efficiency. Trapezoidal slow wave structures (SWSs) with shallow corrugations and long periods are adopted to make the group velocity of TM03 mode at the intersection point close to zero. The coupling impedance and diffraction Q-factor of the RBWO increase, while the starting current decreases owing to the reduction of the group velocity of TM03 mode. In addition, the TM03 mode dominates over the other modes in the startup of the oscillation. Via numerical simulation, the generation of the microwave pulse with an output power of 425 MW and a conversion efficiency of 32% are achieved at 60.5 GHz with an external magnetic field of 1.25 T. This RBWO can provide greater power handling capacity when operating on the TM03 mode than on the TM01 mode.