was fortunate to come across a paper written by the Russian
physicist P. Ufimtsev
, the details of which are:
P.Y. Ufimtsev, "Approximate computation of the diffraction of plane electromagnetic waves at certain metal bodies (I and II)", Sov. Phys. Tech., vol 27, pp 1708-1718, Aug 1957.
This paper detailed a technique which allowed engineers to calculate the non-uniform diffracted (scattered) electric fields from edge shaped discontinuities on conducting radar targets. This technique was combined with the well-known EM scattering approximation known as Physical Optics (PO) into a technique now called the Physical Theory of Diffraction (PTD). This brought a much greater level of accuracy and fidelity into computer-based radar cross section (RCS) modeling which had not been previously available.
It is notable that the Soviet technical community did not see much use for the paper and it was American engineers that saw its potential use.
The PTD was instrumental in the design of the shape of the F117. Using computer simulation to design an aircraft shape which minimizes the RCS is much more economically feasible than making 20 different planes just to measure the RCS.
It is worth noting that the greatest portion of the incident radar energy is NOT absorbed by the F117, but rather scattered in directions other than the direction the incident energy originated. The F117 also has a greater RCS at non nose-on aspects, so it is incorrect to suggest that the F117 has a tiny RCS over all viewing angles. The engine intakes of the F117 are covered not only to reduce the IR signature, but to eliminate the very high multiple-bounce cavity radar returns seen in engine inlets.