Multilevel Physical Optics Algorithm for Near Field Scattering

An algorithm for the fast computation of the physical optics (PO) integral describing single bounce back scattering in near-field scenarios is presented. The algorithm is based on a multilevel computation of partial contributions to the PO integral by hierarchically ordered subdomains. Phase- and amplitude-compensation of the partial contributions allows for their coarse sampling over non-uniform spherical grids. The solution is obtained by gradual aggregation of such partial contributions via interpolation on progressively denser grids. The computational complexity is further reduced by representation of small subdomains´ contributions via their far-field patterns and transition to the near-field representations only at a higher level. Speed-up, accuracy, and error controllability are demonstrated.