Study of the Slow-Wave Properties of a Rectangular Groove-Loaded Folded Waveguide for Millimeter Traveling-Wave Tubes

A novel slow-wave structure (SWS), called the rectangular groove-loaded folded waveguide SWS, is presented in this paper. Its high-frequency characteristics, which include the dispersion properties, normalized phase velocity, and the beam-wave interaction impedance, are analyzed by the field-matching method and calculated numerically. The calculation results by theory agree well with those obtained by the 3-D EM simulation software HFSS. The effects of the groove dimensions on the dispersion characteristics and interaction impedance are specifically studied. It is indicated from this investigation that the modified folded waveguide slow-wave structure with groove loading has the merit of higher interaction impedance but with narrower pass-band and sharper phase velocity dispersion compared to the conventional folded waveguide circuit. With proper groove dimensions, the higher gain and electron efficiency of a rectangular groove-loaded folded waveguide traveling wave tube could be obtained.