Evaluation of the Surface Field Scattered by an Impedance Polygonal Cylinder

Abstract

We have developed a method of evaluation of the surface fields sctattered by an impedance polygonal cylinder when a plane wave is normally incident to the axis of the cylinder. The physical optics (PO) currents are corrected by adding the transtion currents near each edge, which are determined by solving the canonical impedance wedge problem. The uniform asymptotic solutions for the surface fields of the impedance wedge are derived for an arbitrary incident angle, including those for the glancing incidence. It is found that these approximate expressions are very accurate even when an observation point is very close to the edge. When the observation point is far from the edge, surface fields are found to decrease according to (krho)-( 3 / 2 ) and (krho)-( 1 / 2 ) for nonglancing and glancing incidence, respectively. The surface fields may be used to evaluate the near and far fields scattered by a polygonal cylinder with surface impedance through the PO radiation integral. Using the concept of the equivalent current method (ECM), we show how to evaluate the multiply diffracted field. Some numerical results are presented which illustrate the validities of the various asymptotic solutions and the field patterns in the near and far regions.