Transmission characteristics of 0.14 THz terahertz waves in metal overmoded waveguides

Abstract

The transmission characteristics of cylinder and rectangular metal overmoded waveguides frequently used in 0.14 THz frequency band are numerically studied in this paper. At first, skin depths and losses of overmoded cylinder waveguides for different waveguide materials and terahertz wave modes are theoretically calculated and validated by electromagnetic finite difference time domain (FDTD) method. Loss as high as 5 dB/m is obtained for stainless steel and TM01 mode, and it increases with mode orders and decreases with waveguide radius. Also the mode conversion is observed in the straight overmoded cylinder waveguide with finite conductivity. Then transmission characteristics of overmoded rectangular metal waveguide including bend waveguides, straight waveguides, and transition waveguides are researched. The significant mode conversions in the overmoded E and H bend waveguides are found even ignoring the effect of finite conductivity. Only a few of the TE10 mode within frequency band of 0.13-0.16 THz is successfully transported through the standard bend waveguides in Ka band. The transmission characteristics of overmoded straight rectangle waveguide are almost the same as the cylinder one’s. Non-cutoff modes for the two waveguides connected by transition waveguide can transfer through it without losses, while the rest modes can’t.