The folded double-ridged waveguide structure is presented and its properties used for wide-band traveling-wave tube are investigated.Expressions of dispersion characteristics,normalized phase velocity and interaction impedance of this structure are derived and numerically calculated.The calculated results using our theory agree well with those obtained by using the 3D electromagnetic simulation software HFSS.Influences of the ridge-loaded area and broad-wall dimensions on the high frequency characteristics of the novel slow-wave structure are discussed.It is shown that the folded double-ridged waveguide structure has a much wider relative passband than the folded waveguide slow-wave structure and a relative passband of 67% could be obtained,indicating that this structure can operate in broad-band frequency ranges of beam-wave interaction.The small signal gain property is investigated for ensuring the improvement of bandwidth.Meanwhile,with comparable dispersion characteristics,the transverse section dimension of this novel structure is much smaller than that of conventional one,which indicates an available way to reduce the weight of traveling-wave tube. The folded double-ridged waveguide structure is presented and its properties used for wide-band traveling-wave tubes are investigated. Expressions of dispersion characteristics, normalized phase velocity and interaction impedance of this structure are derived and numerically calculated. Calculated results using our theory agree well with those obtained by using the 3D electromagnetic simulation software HFSS. Influences of the ridge-loaded area and broad-wall dimensions on the high frequency characteristics of the novel slow-wave structures are discussed. It is shown that the folded double-ridged waveguide structure has a much wider relative passband than the folded waveguide slow-wave structure and a relative passband of 67% could be obtained, indicating that this structure can operate in broad-band frequency ranges of beam-wave interaction. The small signal gain property is investigated for ensuring the improvement of bandwidth.Meanwhile, with comparable dispersion characteristics, the tran sverse section dimension of this novel structure is much smaller than that of conventional one, which indicates an available way to reduce the weight of traveling-wave tube.