Calculated transmission loss for a leaky feeder communication system in a circular tunnel

The transmission loss for a leaky coaxial cable communication system in a circular tunnel is calculated for an idealized model. The transmitting and receiving antennas are electric dipoles that may be located anywhere within the tunnel. For typical cable parameters, the optimum frequency is found to be in the range from 2 to 10 MHz. Calculations reveal that the use of a sparse braid and a high velocity cable will strongly improve the cable-dipole coupling with only a small penalty of a higher attenuation rate.