THEORETICAL AND EXPERIMENTAL APPROACH OF THE PROPAGATION OF HIGH-FREQUENCY WAVES IN ROAD TUNNELS

Characterization of high frequency electromagnetic wave propagation in tunnels has important applications in the field of mobile communicati on. In long tunnels, the amplitude of the electric field radiated by a retransmitting antenna can be easily calculated from a ray theory. Ho wever, for short tunnels, one of the most critical points is either th e radiation towards free space of a mobile station emitting in the tun nel or, on the contrary, the penetration of an external wave inside th e tunnel. This coupling between the inside and the outside is treated through the uniform theory of diffraction. By comparing theoretical an d experimental results, it is shown that this theory leads to adequate prediction of the field variation and allows us to point out the infl uence of parameters, such as the position of the mobile in the tunnel and the influence of the angle of incidence, on the entrance plane of an incomeing external wave.