Demonstration of a Double Flat-Roofed Sine Waveguide Slow Wave Structure With Low Loss for 220-GHz Traveling-Wave Tube

A double flat-roofed sine waveguide (DFRSWG) slow wave structure (SWS) with low loss for 220-GHz traveling-wave tube (TWT) has been demonstrated in this letter. Through the simulation method, it is inferred that this structure has a large coupling impedance and excellent transmission properties. Besides, the experimental results demonstrate that the transmission loss of the circuit is only 0.62–0.75 dB/cm and the return loss is more than 19.3 dB in the frequency band of 210–250 GHz. Eventually, a two-section DFRSWG interaction circuit is designed to achieve stable device performance. Based on the particle-in-cell (PIC) simulation results, it can be predicted that the DFRSWG TWT can generate the maximum output power of 235 W at 220 GHz, which corresponds to a gain of 36.72 dB and an electronic efficiency of 6.06%.