TABLE OF CONTENTS Eugene F.Knott
Having examined some general considerations attending the measurement of radar scattering characteristics, we now consider outdoor test ranges in particular. Although we would prefer the convenience, economy, and security of measuring test objects indoors, most targets are simply too big for us to do so. For example, a target as small as 5 ft should be measured at a range of not less than 500 ft for a test frequency of 10 GHz if we are to satisfy the farfield criterion. Because such distances outstrip the capabilities of even the largest indoor chamber, we are often forced to measure even relatively small test bodies outdoors.
The single most pervasive electromagnetic feature of the outdoor range is the ground itself. We may manage to eliminate or sharply reduce unwanted reflections from the walls of indoor test chambers, but there is little we can do about the reflections from the ground on outdoor ranges. Although the operators of some outdoor ranges have attempted to overcome the effects of this ground plane, the most effective course of action appears to be to accommodate it. The ground-plane effect forces us to maintain a rather rigorous relationship between target height, antenna height, operating wavelength, and range to the target; and in many cases we deliberately pave the range to render its behavior more predictable.
When we manage to accommodate the operating requirements of the ground-plane range, we will discover an enhancement of the sensitivity of our instrumentation system. The theoretical...
