OVERVIEW

There is a great deal of interest in scale-model testing because of the vastly reduced cost of building and testing models instead of full-scale targets. Unfortunately, electromagnetic scaling laws are material-dependent, and one must decide how to scale the various features of the test object.

If the full-scale test object is perfectly conducting (or even reasonably highly conducting), the scaling laws are simple. Given two objects of identical shape and identical electrical size, as measured in wavelengths, their RCS patterns, when normalized to the square of the wavelength, will be identical. That is to say, the normalized patterns of a set of metal objects each ten wavelengths long cannot be distinguished from one another, no matter what their physical size. The wavelength is the only meaningful yardstick.

Different criteria must be used if one hopes to scale the effects of absorbers or dielectric materials, and there is by no means a consensus. Because the properties of absorbing materials generally vary with frequency, there is little hope of finding a scaled material whose dielectric properties vary from 10 to 20 GHz, say, in the same way that those of a full-scale material vary from 1 to 2 GHz in a -scale model, for a material thickness that of the full-scale material.

It may be argued, on the other hand, that the physical thickness and the electrical properties of the absorber to be scaled are probably not as important as the effective absorption of the material at the scale frequency.