Study on two kinds of novel 220 GHz folded-waveguide traveling-wave tube

Two kinds of novel 220 GHz folded-waveguide (FWG) slow-wave structure (SWS) with different electron-beam tunnels are presented for producing a high power and considerable bandwidth. These structures, which have the potential to have a better performance than the conventional FWG SWS, are suitable for circle-beam electron guns and sheet-beam electron guns, respectively. In this study, the electromagnetic characteristics and nonlinear interaction between the electron beam and the electromagnetic field of the two kinds of novel FWG are investigated on the basis of simulation results. The influence of the beam tunnel with respect to its transverse shape and size on the circuit performance is investigated in detail. With different beam tunnels, the two novel FWGs exhibit similar radio-frequency characteristics and signal gain. Particle-in-cell simulation results reveal that the novel tubes exhibit a gain greater than 32 dB and a bandwidth of 10% with a 16.5 kV and 150 mA electron beam and a 90 mW peak input power. Compared with the conventional FWG SWS, the novel FWGs have 32% higher output power under optimized conditions.