Propagation properties of dielectric-lined hollow cylindrical metallic waveguides for THz waves

For the rigorous analysis of the propagation properties of dielectric-lined hollow cylindrical metallic waveguides operating in the THz range of frequencies, the characteristic equation for propagation constants is derived from the electromagnetic field equations and the boundary conditions of the dielectric-lined waveguides. The propagation constant of the dominant hybrid HE11 mode can be obtained by solving the characteristic equation with the improved Muller method. The classical relaxation-effect model for the conductivity is adopted to describe the frequency dispersive behavior of normal metals for the metallic waveguide wall. For a 1.8 mm bore diameter silver waveguide with the inner surface coated with a 17 m-thick layer of polystyrene(PS) film, the transmission losses of HE11 mode can be reduced to the level below 1 dB/m at 1.5~3.0 THz, and the dispersion is relatively small for HE11 mode. In addition, with the PS film thickness increasing, the transmission losses of HE11 mode increase first and then decrease for a 2.2 mm bore diameter silver waveguide at 2.5 THz, and the minimum loss can be achieved by adopting the optimum dielectric layer thickness.