A uniform GTD treatment of surface diffraction by impedance and coated cylinders

In the context of the uniform geometrical theory of diffraction (UTD), computation of the scattered fields near the shadow boundary of a smooth convex surface requires values for the Pekeris-integral function p*(/spl xi/,q). While in a small number of cases such as the case of perfect conductivity (q=0 and q/spl rarr//spl infin/), tabulated values of the function are available; in the general case, these values must be obtained by some numerical method. A procedure for approximating p*(/spl xi/,q) by residue-series means is introduced. In contrast with traditional residue-series representations, the new procedure requires only a limited knowledge of pole locations even in the shadow boundary transition region and thereby extends the regime of practical applicability of residue-series methods beyond the deep shadow. It is demonstrated that the new procedure can be combined with an earlier residue-series representation derived by Hussar and Albus (1991), and with geometrical optics, to provide a computationally efficient procedure for computing fields scattered by an impedance or coated cylinder.