Far-field scattering with fast hybrid integral equation based-ray optical method

In this paper, the hybrid finite element - boundary integral - multilevel fast multipole method - uniform geometrical theory of diffraction (FEBI-MLFMM-UTD) technique is extended in order to efficiently overcome the drawbacks of ray optical methods in predicting scattered far-fields. This is obtained using planar near-field scanning techniques for dealing with ray optical terms of the scattered field. Particularly, scattered ray optical fields are first computed in a scanning plane in the near-field region of the involved objects. These computations are accelerated by MLFMM. After that, the near-fields are transformed into far-fields using standard plane wave spectrum expansions. Direct contributions to the scattered field are computed directly in the far-field using conventional fast techniques, so that no evanescent waves are present in the scanning plane. Angular far-field limits are caused by scan plane truncation and aliasing due to less sampling rates than the Nyquist rate. Full angular coverage is achieved by combining solutions for multiple scanning planes.