EM propagation in tunnels

Abstract
This paper gives a brief review of various aspects of electromagnetic (EM) wave propagation in tunnels and of radio communication in such media. First a quantitative description is given for the propagation in empty tunnels and in tunnels containing axial conductors or leaky feeders. The limitations of such simplified approaches are stressed. A review of quantitative studies of these phenomena is then presented. Engineering considerations are briefly mentioned. Attention is drawn to mode conversion techniques, which play an important role, and to the multimode operation of systems. It is concluded that the theoretical aspects of EM wave propagation in tunnels are currently well understood, although work remains to be done on wide-band and microwave communication systems