A Novel Slow-wave Structure — Coupled Double Folded Waveguide Operating at High-order TM20 Mode for Terahertz TWT

A slow-wave structure named coupled double folded waveguide (CDFW) is proposed for traveling wave tube operating at terahertz region. Its electromagnetic characteristics and beam-wave interactions are presented in this paper. This structure, evolved from a single folded double ridge groove waveguide (DRGW) by intersecting the groove along its transverse direction, can operate at high-order TM20 resulting in increased horizontal dimension. Furthermore, this novel CDFW can interact with two pencil beams and have high beam-wave coupling impedance, which is beneficial to output high power at terahertz band. The proposed CDFW, when applying a dynamic velocity taper technique, can produce an output power of 210 W at 340 GHz with a 3-dB bandwidth of 13 GHz, and it is 80 W higher than a folded DRGW with a single beam at the same condition, when the beam voltage and beam current are 27.98 keV and 0.25 A, respectively.