Fresnel zones for ground-based antennas

The ordinary Fresnel zone concept is modified to include the influence of finite ground conductivity. This is important for ground-based antennas because the influence on the radiation pattern of irregularities near the antenna is determined by the amplitude and phase of the groundwave. A new definition of Fresnel zones which takes into account the phase shift of groundwave propagation is given and it is shown that these new zones are zones of greatest influence, at least when discontinuities of the electrical parameters of the ground are considered. Numerical results for the first Fresnel zone are given, and it is shown that the zone is much smaller for a finite conductivity than for an infinity conductivity, especially for small angles of elevation.