Improved Physical Optics Computation Near the Forward Scattering Region: Application to 2-D Scenarios

The classical physical optics (PO) formulation of the scattered fields suffers from the loss of accuracy when the observation angle widely deviates from the specular direction. This is even worse in the "forward region,"; i.e., for the bistatic angles between 90 degrees and 270 degrees. The method presented in this article aims at improving the accuracy of the fields in this region by finding the currents induced on the nonilluminated part of the object, where the classical PO assumes zero currents. The proposed approach reformulates the initial problem using equivalent currents over a domain surrounding the object. The equivalent currents then act as new sources that induce electrical currents computed by the classical PO formulation. The computation of the equivalent problem is accelerated using the multipole expansion of Green's function, including appropriate singularity extraction in the very near field. This approach provides an error that is significantly lower in the forward direction than the classical PO formulation. The principles of this new approach are presented and validated for the 2-D scenarios.