Transmission line analysis for the electromagnetic wave propagation characteristics in tunnels

摘要

The tunnel environment is so complex that the study on the characteristics of electromagnetic waves propagation in a tunnel is very difficult. Based on the equivalent transmission line method, which combines electromagnetic field and circuit theory, the wave-guiding characteristics in a tunnel are easily analyzed. As examples, the transmission line model of horizontal polarization and vertical polarization electromagnetic waves in rectangular tunnel are built. Furthermore, numerical analysis is performed. The results indicate that a tunnel radio signal consists of a summation of many propagation modes. The electric field strength decreases with the increase of the propagation distance, and the higher frequency, the lower loss. The receiving signal of the center tunnel is the strongest. In a rectangular tunnel, the height has a great effect upon the propagation characteristics of the vertical polarization wave modes, and the width has the same effect upon the horizontal polarization wave modes. Moreover, the relative dielectric constant of wall rock exerts little influence.