Fast field back-propagation using a multilevel non-uniform grid algorithm in oblate spheroidal coordinates

The Rayleigh-Sommerfeld (RS) back-propagation method is accelerated by a modified version of the multilevel nonuniform grid algorithm (MLNG). The algorithm utilizes oblate spheroidal grids to be effective in terms of the number of sampling points that are required for correct reconstruction of the fields measured on quasi-planar surfaces. The method is demonstrated on the example of a parabolic reflector with a surface distortion. A good agreement between the results of the direct RS integration and the proposed method is achieved.