RF propagation in tunnel environments

A review of radio propagation in subterranean tunnels is presented. Such environments are of interest for homeland security as subways are a vulnerable target, and in a military context. A theoretical analysis of the waveguide nature of tunnels is presented along with the loss mechanisms due to surrounding walls. Propagation losses associated with corners, bends and antenna coupling are also presented. Modeling techniques such as finite difference, time domain, parabolic approximations and ray tracing approximations are discussed and some numerical results for straight, curved and cornered tunnels are presented.