Terrain effects on antenna radiation patterns

A numerical method for calculating the scattering and diffraction at an antenna site to be used in a sky-wave communication link is derived. The method of physical optics is used to treat the scattering by the terrain surrounding the antenna site. The terrain is represented by a Gaussian transformation and, as an intermediate step, the reflection points on the terrain are found. The method is compared with the approach based on the numerical solution of an integral equation and good agreement is obtained. It appears that the method will be applicable over the HF range for the majority of terrain encountered in practice.