Diffraction by Canonical Metallic and Material-Coated Structures: A Review

Keller's landmark paper in 1962 formulated the Geometrical Theory of Diffraction (GTD). This was the beginning of a long process that brought the Geometrical Theory of Diffraction into practice, making it one of the most ubiquitous analysis methods in electromagnetics. This paper provides a personal historical trace of the Geometrical Theory of Diffraction: in particular, its further development in the 1970s and 1980s, and its realization into computer codes. The latter provided the first step for the analysis of complex realistic structures. The second half of the paper discusses the historical development of diffraction coefficients for impedance wedges using first- and higher-order generalized impedance boundary conditions.