SHADOW BOUNDARY CURRENTS IN THE PROBLEM OF HIGH-FREQUENCY ELECTROMAGNETIC DIFFRACTION BY A CIRCULAR IMPEDANCE CYLINDER

A correction of the physical optics approximation by accounting for th e presence of specific currents concentrated near shadow boundaries on the surface of a convex nonmetallic scatterer is analysed by consider ing a canonical problem of diffraction of a plane electromagnetic wave incident normally to the axis of an infinite circular cylinder with i mpedance boundary conditions. The analysis focuses on the development of Fock-type asymptotic representations for magnetic field tangent com ponents on the surface of the scatterer. The Fock-type representation of the surface field is uniformly valid within the penumbra region, pr oviding a continuous transition From the geometrical optics formulas o n the lit portion of the surface to the creeping waves approximation i n the deep shadow region. A new numerical procedure for evaluating Foc k-type integrals is proposed that extracts rapidly varying factors and approximates the rest, slowly varying coefficients via interpolation. This allows us to obtain accurate and simple representations for the shadow boundary currents that can be directly inserted into the radiat ion integral and effectively integrated. We show that accounting for t he shadow boundary currents considerably improves the traditional PO a nalysis of the high-frequency electromagnetic fields scattered from sm ooth and convex non-metallic obstacles, particularly near the forward scattering direction.