Backscattering from Electrically Large Low-Absorption Spheres

Abstract

Backscattering from electrically large low-absorption spheres cannot be fully explained in the framework of geometrical optics. This paper studies the role of the so-called horizontal branch of poles of the spectra and shows that the residues at these poles can be interpreted as creeping waves propagating on the concave side of the spherical boundary. In contrast to the well-known creeping waves propagating on the convex side of the spherical boundary, which are associated with the vertical branch of poles and rapidly decay with growing electrical size of the sphere, these new waves are much weaker attenuated and may dominate backscattering from electrically large low-absorption spheres. Analytical formulas for the contributions from the poles of the horizontal branch are obtained, and their relation to the irregular pattern (ripple) in scattering cross sections of electrically large low-absorption spheres is suggested.