Hilly site L-band antenna fade

The decrease of antenna gain from its free space value (the fade) of an L-band fan beam beacon antenna deployed in a hilly site is considered, taking into account sensor coverage at low elevation angles. It is pointed out that the two established models, flat earth and uniform roughness, do not give an adequate description of fade for a hilly site. A description is given of a method which attempts to overcome the limitations of previous approaches for assessing fade. The described method uses a terrain model that accounts for hills independent from general roughness and takes into account the diffraction of the direct field at elevations grazing the horizon.