Radio Wave Propagation in Tunnels

TL;DRAbstract

This report examines the radio propagation model for narrow and long tunnels. Modal analysis is used to model the path gain in 2-D and 3-D rectangular tunnels and the coupling loss of L, T and cross tunnels. Modal attenuation is determined by the wavelength lamda and given tunnel dimension through the factor square lamda /cubic w where w is the width of tunnel, by the mode number and dielectric constant of the walls. In oversized tunnels, many nodes ma) propagate, however higher modes have high attenuation constant so that a few lower modes are dominant at long distances from the transmitter. The antenna polarization giving the least path loss in 3-D tunnels, is found by comparing attenuation constants of both vertical and horizontal polarization. For the propagation into branches off the main tunnel, mode coupling at the discontinuities is obtained by hybrid ray-mode conversion. By accounting for the mode diffraction at each comer, we compute the coupling loss into cross junctions, th

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