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A theoretical model for calculation of the high frequency characteristics of the sine waveguide slow-wave structure (SWS) is proposed. The formulas of dispersion and interaction impedances of the hybrid modes are obtained by combining the Helmholtz equation with the appropriate boundary conditions. Using the full wave analysis method, it is proved that the periodic structures with a half-period shift followed leads to a pairwise closing of passbands characteristic of adjacent mode. The sine waveguide SWS for 0.22THz traveling wave tube (TWT) is chosen as an illustrative example to verify the validity of the theoretical model, and the calculation results of the dispersion curve and interaction impedance curve are consistent with the HFSS simulation results. In addition, the influences of dimensions of sine waveguide on the high frequency characteristics of +1st spatial harmonic wave are investigated by numerical calculation. The study indicates that the appropriate SWS parameters are helpful for improving the bandwidth and increasing output power of TWT.