EM propagation in tunnels

Various aspects of electromagnetic wave propagation in tunnels and of radio communication in such media are reviewed. A quantitative description is given for propagation in empty tunnels and in tunnels containing axial conductors or leaky feeders. The limitations of such simplified approaches are stressed. Quantitative studies of these phenomena are then reviewed. Engineering considerations are briefly mentioned. Attention is drawn to mode conversion techniques 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 wideband and microwave communication systems.>