VHF ELECTROMAGNETIC WAVE PROPAGATION.

Some of the conventional approximations used in modelling the propagation of electromagnetic waves at short wavelengths are no longer valid for communications systems operating at meter wavelengths. Moreover, specific effects appear at very high frequencies which must be taken into account. This paper first deals with the various influences of the ground on VHF propagation, both from a theoretical point of view by means of a numerical model based on classical theories, and from an experimental point of view by means of actual measurements and comparison with theory. It is concerned with the application of such models to the estimation of the performances of an air surveillance VHF radar. Finally, it is shown that such radars are sensitive to certain spurious echoes which are specific to these frequencies, an interesting example of which is specular reflections on high-altitude ionized meteor trails. 14 refs.