Characterization of UHF radio propagation channel in curved tunnels

We propose an imperfect waveguide model to represent empty curved tunnels. We use the field configuration in an optical dielectric guide together with the surface impedance boundary condition for the walls to simplify the complexity of derivation of the propagation modal equations. The curvature of the tunnels is assumed to be gentle. Our results show that increased propagation loss is almost linearly proportional to frequency and inversely proportional to the radius of curvature.