Group velocities of a surface electromagnetic wave along an impedance two-layer medium

The propagation of a surface electromagnetic wave in a two-layer impedance medium is considered. Based on the Leontovich-Lighthill-Rytov identity theorem, the velocities of group waves in each layer of a two-layer model of a highly inductive impedance medium are established. It is found that in the atmosphere, the group velocity is slightly less than the speed of light in a vacuum and is different from the phase velocity of the wave; in the dielectric first layer, the group velocity depends on the permittivity of the medium and is also less than the speed of light; in the conducting second layer, the conducting base of the two-layer medium, the group velocity is noticeably less than the speed of light.