Enhancement of rectangular tunnel waveguide model

Abstract

The ray theory is applied to locate the break point to distinguish propagation regions for line-of-sight topographies in rectangular tunnels. It is found that path loss in tunnels differs greatly in the regions prior to and after the break point. Nevertheless at least two waveguide modes are needed to accurately model tunnel natural propagation. In addition, the errors in the formulas to calculate the losses due to roughness and tilt of the tunnel walls are corrected. As a result, the propagation loss prediction of the rectangular tunnel waveguide model is significantly enhanced.