Application of geometric diffraction theory to scattering from cones and disks

The ability of the geometrical theory of diffraction to predict the radar cross section (RCS) of a perfectly conducting, right circular cone as a function of viewing angle is evaluated by comparison of computed and measured values of RCS. Both vertical and horizontal polarization have been considered for cones ranging from 0.98 to 2.87 wavelengths in diameter at the base and having half angles of 4°, 15°, and 90°; the latter case corresponds to a disk. It is shown that for cones having normalized base circumference (ka) of 8 or 9 the predicted and measured RCS agree very well except when the cone is observed within about 30° of nose-on with vertical polarization, in which case large errors occur for some as yet unknown reason. For smaller cones having diameters about equal to the wavelength (ka around 3), the computed RCS is generally predicted within 5 dB, but the form of the RCS pattern is not predicted very accurately. Backscattering from the base of the cone is very nearly the same as backscattering from a disk of the same diameter for viewing angles within 60° of the normal to the base.