Analysis of the high-frequency characteristics of a sine waveguide

Abstract

Based on the double-periodic characteristics of a sine waveguide, the dispersion equation, interaction impedance, and transmission losses of slow-wave structures are derived. The dispersion equation indicates that the waves propagating in the sine waveguide should belong to two mode types, which can exist independently rather than as “pseudo-modes.” The dispersion equation, interaction impedance, and transmission losses are obtained using a theoretical model. A 220 GHz traveling wave tube (TWT) is used as an illustrative example to verify the validity of the analytical model. The calculated results show that the dispersion curve is in good agreement with that given by the Ansys high-frequency simulation software over the entire frequency range and that the theoretical numerical calculation time is less than 2% of that of the Ansys software package. In addition, the results demonstrate that the interaction impedance of the symmetric φ0 + π mode is much higher than that of the asymmetric φ0 mode. Therefore, the symmetric φ0 + π mode should be used for propagation in sine waveguide traveling-wave tubes. Moreover, when the conductivity is set at 1.6 × 107 S/m, the loss of the sine waveguide is ∼1.15 dB/cm for 220 GHz. The equivalent conductivity of the metal can be used appropriately in the design of the mm-wave and the THz TWT.