Near-field scattering by physical theory of diffraction and shooting and bouncing rays

The problem of electromagnetic wave scattering is very important in defense applications. The research on this topic was mostly centered on far-field analysis: assume an incident plane wave, compute its scattered field due to the scatterer, and evaluate the radar cross section (RCS) of the scatterer. When the transmitting and receiving antennas are far from the scatterer, the incident wave can be approximated by a plane wave on every part of the target, the far-field analysis thus applies. However, in practical applications, there are many situations that the distance between the transmitting antenna and the scatterer is not large enough to treat the field arriving the scatterer as a plane wave. In these conditions the far-field analysis is not valid, and a near-field analysis is necessary. Most scattering papers on academic journals are related to the far-field analysis. The only near-field study that the author knows is the NcPTD code developed in DEMACO by Lee (1991). However, in this study only the physical theory of diffraction (PTD) is modified to deal with near-field scattering of convex scatterers. The method of shooting and bouncing rays (SBR), which is useful in evaluating the far-field RCS of concave targets, was not included. Also, the formulae are not explicit. This paper presents the PTD and SBR formulae for near-field scattering from a unified view.