ON THE SOLUTION OF A CLASS OF LARGE-BODY SCATTERING PROBLEMS VIA THE EXTRAPOLATION OF FDTD SOLUTIONS

The objective of this paper is to apply an extrapolation technique in conjunction with the FDTD method to solve scattering problems involvin g a class of large three-dimensional metallic objects in a numerically efficient manner. The extrapolation technique is based on the observa tion that, for sufficiently high frequencies, the field variation near the surface of the scatterer exhibits a certain simple frequency depe ndence and that the knowledge of this behavior can be used to evaluate the induced current at frequencies where the body size is too large t o be tractable via direct methods. The solution process begins with an application of the FDTD to obtain the field distribution on a surface enclosing the scatterer over a wide band of frequencies. The computed results in the upper end of the spectrum, where the body size is at l east moderately large, are retained and these field solutions are proc essed by using the generalized pencil of function (GPOF) method to ext ract the constituent traveling wave components, that usually number on ly 2 or 3. Finally, the functional frequency dependences of the travel ing wave components are extracted and used to derive the extrapolated solutions at higher frequencies. It is demonstrated that the above ext rapolation procedure can be applied to a class of three-dimensional sc atterers, even at the grazing incidence and in the shadow region, wher e the asymptotic methods are known to suffer from accuracy problems. A n important observation regarding the extrapolation technique is that, In contrast to the direct methods, e.g., the FDTD - and MoM, the extr apolation technique is not constrained, in principle, by any CPU time and memory limitations at high frequencies.