Ray and Caustic Asymptotics for Edge Diffracted Waves

Abstract

The asymptotics for edge-diffracted waves can be presented in another form that reveals their ray structure. Ray asymptotics were postulated in the geometrical theory of diffraction (GTD). GTD can be interpreted as the ray asymptotic form of physical theory of diffraction (PTD) for total diffracted field. In contrast to PTD, GTD is not applicable in regions where the field does not have a ray structure and where the actual diffraction phenomena happen. The ray asymptotics are not valid at caustics, where they predict an infinitely large field intensity. Caustic asymptotics are presented for both acoustic and electromagnetic waves. These asymptotics have the same structure and differ only in the coefficients. This chapter discusses the relationships between PTD and GTD. PTD is a source-based technique and GTD belongs to ray-type theory.