Dual-Band Operation of Relativistic BWO With Linearly Polarized Gaussian Output

We demonstrate the dual-band operation of a relativistic backward wave oscillator (RBWO) whose output is a linearly polarized TE11-mode. The RBWO consists of two cylindrical sections with sinusoidal corrugations where the downstream section is axisymmetric and the upstream section has combined left- and right-single-fold spiral corrugations. We show that generation of 10 GHz is realized when the axisymmetric section operates as a BWO with the operating TM01-mode and the combined spiral section operates as a Bragg reflector that converts the backward TM01-mode to a linearly polarized forward TE11-mode. For the same electron beam parameters, generation of 7 GHz is realized when the combined spiral section operates as a BWO with the operating TE11-mode. We also present the possibility to change the duration of generation at each frequency within a microwave pulse by changing the electron beam current. In addition, one can change the output frequency by changing the values of the guide magnetic field near the region of cyclotron absorption.