A THz Backward-Wave Oscillator Based on a Double-Grating Rectangular Waveguide

A double-grating rectangular waveguide system with a round beam channel is proposed as the slow-wave interaction structure of a terahertz (THz) backward-wave oscillator (BWO). Applying the latest microfabrication techniques, the interaction structure is fully realizable and easily assembled. The basic design principle including the beam-wave dispersion relation, interaction impedance, and the system configuration is presented. A detailed sensitivity analysis of this THz BWO circuit is carried out to investigate the structure errors caused by fabrication and brazing. Both upstream and downstream ends are loaded with step tapers to improve the voltage standing wave ratio. The downstream reflection is absorbed by a linear attenuator. The round electron beam is generated by a pierce gun with compression ratio of 15. A 3-D particle-in-cell simulation demonstrates a broad electronic tunable bandwidth, a 3-dB bandwidth exceeding 28 GHz with highest output power 16 W, and interaction efficiency 3.57%.