5.1 OVERVIEW

We have seen in Chapters 3 and 4 how scattering solutions may be affected in the Rayleigh and resonant regions, and in this chapter we will discuss high-frequency RCS prediction techniques. It must be emphasized at the outset that the term high frequency refers not so much to the actual frequency of the incident wave as to the size of the target when compared to the incident wavelength. In the highfrequency range, the scattering obstacle should be at least five wavelengths in size, although reasonably accurate results may be obtained for some bodies even smaller than this.

The high-frequency region is of great practical importance, as may be seen from a consideration of typical threat radars and targets. Threat radars range from low-frequency systems used for surveillance to the higher frequencies used for fire control and command-guided surface-to-air missile systems. Long-range surveillance radars use frequencies down to the VHF region or lower because the signals propagate well beyond the visible horizon. The wavelengths can be as long as about 10m, hence airborne targets are not likely to be more than two or three wavelengths in size. This is the edge of the high-frequency RCS region, and high-frequency prediction techniques may not be useful for such targets. However, the wavelengths of radars operating in the UHF bands are on the order of a meter or shorter, hence most airborne target will be at least 10 wavelengths long. At fire control radar wavelengths, the targets may be hundreds...