Abstract:Because of the huge ohmic losses of the fundamental mode waveguide in terahertz wave, over-mode transmission line is often adopted to reduce the transmission loss. Nevertheless, the waveguide mode would be changed by using over-mode transmission line. How to ensure the stability of the mode is an important issue. By using simulation and experimental methods, the stability of the circular waveguide at 220 GHz is researched. The results show that prolonging taper waveguide properly can inhibit the mode change and maintain single mode.