A Groove-Loaded Folded Waveguide Slow Wave Structure With Vertical Beam Tunnel for Power Enhancement in Sheet Beam Sub-THz TWTs

To enhance the output power and beam–wave interaction efficiency of sheet beam (SB) traveling wave tubes (SB-TWTs) operating in the subterahertz frequency range, this study proposes a novel groove-loaded folded waveguide (GLFW) slow wave structure (SWS) with a vertical beam tunnel. GLFW-SWS overcomes size limitations associated with operating frequency, thereby allowing for a broader lateral dimension of the beam tunnel. It effectively expands the width of the beam tunnel while minimizing reflection. Compared with the traditional folded waveguide (FW) SWS, the average interaction impedance in the interaction region is increased by 50%. In the subterahertz frequency range (218–220.5 GHz), the utilization of GLFW-SWS leads to a great improvement in the output power level of the TWT. Combined with a phase velocity tapering optimization method, at cathode voltages and current of 25 kV and 0.4 A (focused current density of 341 A/cm2), respectively, output power exceeding 1.01 kW can be achieved at 219.6 GHz. The interaction efficiency is over 10.1%. The transmission and dispersion characteristics are experimentally verified. This development offers a promising solution for subterahertz sources in next-generation communication.