A G-Band Traveling Wave Tube Based on Mode Selection Circuit for Suppressing Backward Wave Oscillation

To suppress the backward wave oscillations in traveling wave tube (TWT) amplifiers, which are caused by the high gain of higher-order modes, mode selective folded waveguide (MSFW) is proposed as a slow wave structure (SWS). The MSFW consists of folded waveguide (FW) and mode selective circuit (MSC). Specifically, the MSC is made up of two segments of discontinuous rectangular waveguides. Consequently, the MSC can realize the suppression of the higher-order modes of the FW effectively and thus improve the performance of the FW-TWT. The simulation results show that the single-segment MSFW-TWT has a 3-dB bandwidth of 212.5–218.5 GHz, a saturated output power of more than 72 W, and a maximal gain of 39.59 dB. Meanwhile, the risk of the TWT’s backward wave oscillations is greatly reduced. As a result, the great potential of MSFW as a terahertz (THz) amplifier can be clearly seen from these results.