Propagating modes on a buried leaky coaxial cable

Characteristics of the discrete propagating modes on a buried leaky coaxial cable are investigated in this report. Provided the transfer inductance of the braid is small, three distinct propagating modes for most of the cable depths were found. The first mode has a field structure closely associated with the TEM-mode of a coaxial line and referred to as a bifilar mode because of its almost equal but opposite current on the two conductors. The second mode has a field structure located mainly outside the cable in the earth region and is referred to as a monofilar mode. The third mode which exists only for certain cable depths has a field more spread out over the air-earth interface and is referred to as a surface-attached mode. Unlike the case of an elevated wire, no degeneracy of modes is observed for parameters of practical interest.