Propagation characteristic of guided electromagnetic waves in a circular tunnel

Mode equations are given in a circular tunnel that contains an axial conductor or two axial conductors, and they are solved through numerical analysis method, and the main conclusions we obtain are as follows: in tunnels, when there are axial conductors, it is beneficial for EM waves to propagate; it is more favorable for EM waves if the conductivity of conductor or tunnel is bigger, tunnel radius is larger and separation distance between conductor and tunnel becomes larger; the attenuation rate of bifilar mode is smaller that of monofilar mode, when the interval between two conductors is not big, and the EM field of it concentrates between the two conductors, and almost isn't affected by surrounding media.