Bandwidth of a Leaky Coaxial Cable in a Circular Tunnel

Using the idealized model of a leaky coaxial cable in a circular tunnel to represent a leaky-feeder communication channel, we examine both pulse transmission and the bandwidth limitations of the channel. The phase and group velocities of the bifilar mode are found to be nearly independent of frequency between 1 MHz and 100 MHz, and the channel bandwidth is found to be quite large. The effect of mode excitation is also examined by treating the mutual impedance between a pair of short electric dipoles as the transfer function and the channel bandwidth is still large.