Theory and experiment of a mobile radio communication in tunnels by means of a leaky braided coaxial cable

To realize a radio wave communication along mine galleries a few kilometers long without repeater, we show that it is possible to use a leaky braided coaxial cable, with an inductive coupling to the tranceivers. By using the transmission line theory, we determine the optimal electrical and geometrical constants of the cable. A communication 2 km long has been demonstrated for a total transmission loss along the line of about 70 dB. We also account for the possibility in which the cable is situated close to the wall along a short distance and we show that the increase in attenuation of the monofilar mode does not have a great influence on the performance of the cable. The theoretical approach is confirmed by experimental data for a number of specific cases.