Fast computation of double bounce contributions to physical optics integrals in the near field

A multilevel algorithm for the fast computation of double bounce (DB) contributions to near field (NF) scattering physical optics (PO) integrals is presented. The algorithm aims at accelerating the computation of the mono-static DB contribution for multiple excitations, i.e., for sources set within a wide range of locations with respect to the scatterer, and over a range of frequencies. The DB-NF fast PO algorithm is an extension of its far field predecessor (A. Boag and E. Michielssen, IEEE Trans. Antennas Propag., 52, 205–212, 2004) and it complements our fast NF algorithm for computing the single bounce PO contribution (A. Gendelman, Y. Brick, and A. Boag, IEEE Trans. Antennas Propag., 62, 4325–4335, 2014).