OVERVIEW

After describing the typical configuration of the ground-plane range in this chapter, we discuss the main feature influencing its design and operation: the ground itself. We resort to idealizations of the ground plane using omnidirectional antennas at first, but then we become a bit more realistic by investigating the effects of directive antennas and imperfectly conducting soils. At the end of the chapter we analyze two methods of defeating the ground plane, both of which have been abandoned in practice, even though the analysis suggests that one may be reasonably effective.

We deal with the ground plane because it is unavoidable. In the presence of the ground, the target is illuminated by two distinct fields, one of them arriving directly from the transmitting antenna and the other via a reflection off the ground. Scattered energy reaches the receiver by means of the same two paths, and in most cases the result is an enhancement of the received signal over that that might be received in the absence of the ground plane. That enhancement is influenced by the reflection characteristics of the ground and the radiation patterns of the antennas. But because the incident field is no longer as uniform as it would be without the ground plane, four parameters must be played against each other to optimize target illumination: frequency, range, antenna height, and target height.

Because frequency is hardly ever held fixed in modern RCS measurements, and because the vertical location of the peak in the multipath interference...