Design and Experiment of Modified Folded Waveguide Slow Wave Structure for 60-W G-Band Traveling Wave Tube

A modified folded waveguide (MFWG) slow wave structure (SWS), where the beam-tunnel wall in the conventional folded waveguide (CFWG) is partially removed, has been proposed for THz traveling wave tubes (TWTs). Compared with the CFWG, MFWG provides a wider operating bandwidth, lower circuit loss, and stronger longitudinal electric field, indicating higher interaction efficiency with significant bandwidth. Meanwhile, MFWG has stronger heat dissipation performance indicating high duty cycle and even continuous wave capability. Given these aforementioned advantages, the analysis, design, fabrication, assembly, and hot test of the MFWG-SWS were carried out for a TWT at G-band. With beam parameters of 22.4 kV and 58 mA, this TWT produces a maximum of 62.5W, around 217 GHz, corresponding to a saturation gain of 40.2dB. The measured 50 W power bandwidth exceeds 3 GHz. More importantly, the tube can work up to 40% duty cycle. The above experiments indicate excellent performance of the MFWG for application in THz TWTs.