A THz High-Order Mode Operation BWO Based on a Composite Structure

A 660 GHz high-order mode operation backward wave oscillator (BWO) is proposed based on a novel composite structure. The fundamental mode oscillation can be suppressed by inserting another slow wave structure (SWS) with a forbidden band close to the competition frequency, destroying the excitation condition and increasing the insertion loss for the competition frequency, therefore, cutting off the signal loop. The cold test demonstrates that the composite structure can increase the insertion loss for the fundamental mode over a frequency band. Driven by a 10 mA ideal beam in the particle-in-cell (PIC) simulation, the composite structure BWO operates stably in high-order mode, with a tuning frequency range of 651.5 GHz to 665.1 GHz as the operating voltage varies from 18 kV to 20 kV, achieving an output power of over 450 mW. This validates the effectiveness of the method in suppressing fundamental mode oscillation.