INCREMENTAL LENGTH DIFFRACTION COEFFICIENTS FOR THE SHADOW BOUNDARY OF A CONVEX CYLINDER

Incremental length diffraction coefficients (ILDC's) are obtained for the shadow boundaries of perfectly electrically conducting (PEC) conve x cylinders of general cross section. A two-step procedure is used. Fi rst, the nonuniform (NU) current in the vicinity of the shadow boundar y is approximated using Fock functions, The product of the approximate d current and the free-space Green's function is then integrated on a differential strip of the cylinder surface transverse to the shadow bo undary to obtain the ILDC's, This integration is performed in closed f orm by employing quadratic polynomial approximations for the amplitude and unwrapped phase of the integrand, Examples are given of both the current approximations and the integration procedure. Finally, as an e xample, the scattered far field of a PEC sphere is obtained by adding the integral of the NU ILDC's of a circular cylinder along the shadow boundary of the sphere to the physical optics (PO) far field of the sp here. This correction to the PO field is shown to significantly improv e upon the accuracy of the PO far-field approximation to the total sca ttered field of the sphere.