TABLE OF CONTENTS The discussion of RAM to this point has concentrated on the reduction of specular, or mirrorlike, radar returns. As has been noted in all of the earlier chapters that discuss design guidelines, the first tool to be employed in RCSR is shaping, and the goal of shaping is to eliminate all specular returns in the primary threat sectors. Obviously, if that goal can be accomplished, specular RAM has a very small role in RCSR design, and the reduction of nonspecular returns requires the focus of our attention. However, although significant progress is being made in the application of nonspecular absorbers, the theory necessary to support a design methodology is not nearly as well understood as for the specular case.
Nonspecular returns arise from surface traveling waves, edge waves, and creeping waves. In addition, the returns from gaps and cracks and edge diffraction are also often classed as nonspecular returns. The characteristic that distinguishes most of the mechanisms of interest in nonspecular scattering is that they are due to surface currents along the direction of propagation and are therefore spatially extended effects. For this reason, the optics formalisms that apply to specular RAM design are, in general, not appropriate for nonspecular RAM design.
In this section two different areas of nonspecular RAM design are explored. The first discusses the use of magnetic or dielectric surface coatings to reduce surface currents and hence reduce traveling and creeping wave returns. The second area concerns the use of tapered...
