Design of Q Band Folded Waveguide Slow Wave Structures with Phase Velocity Taper Near Cutoff Region

A design of Q band folded waveguide(FWG) slow wave structure(SWS) with phase velocity taper is introduced in this paper. The novel design of slow wave structure is expanded from a conventional folded waveguide SWS. The SWS is designed to suppress oscillation and broaden bandwidth. Distinguished from the existing phase velocity tapering SWS, part of operating frequency is lower than the cutoff frequency of one section. The simulation results show that the output power is about 158W in a frequency range of 44-52GHz, with a 19-kV, 140-mA electron beam. The maximum output power and gain is up to 320W and 44dB, respectively. The electronic efficiency is over 6%.