Reflection and diffraction for lossless and lossy dielectrics in the near-far-near FDTD method

The effects of electromagnetic scattering are often tested at electromagnetic scattering ranges. These ranges are comprised of a level field with antenna arrays at one end and a target object at the other end. A variety of antennas and antenna arrays are used to determine the scattering signatures of various objects. However, analyzing these scattering ranges in the time domain requires more computer memory and computation time than is practicable. This is due to the great size of the range itself. A novel approach had been devised here that accurately models these ranges for an antenna and a target over a ground plane of arbitrary permittivity and conductivity. This approach also models diffraction effects that occur due to discontinuities in the ground plane near the scattering target. This method maintains a high level of accuracy while drastically reducing the amount of computational resources that are required to perform the calculation versus the using traditional Finite-Difference Time-Domain method. The new method is applied in general to cases where there is a significant separation between an electromagnetic source and a target scatterer.; The Finite-Difference Time-Domain (FDTD) method is a widely used numerical technique for determining the interaction of electromagnetic fields with objects of arbitrary shape and material composition. In general, it is difficult or impossible to determine the electromagnetic interactions with a closed-form solution of Maxwell's Equations. The FDTD method is relatively easy to program, but it requires a large amount of computer memory and computation time. As the problem size increases, the needed computer resources increase with it. This makes the FDTD method impractical for problems in which the source of the electromagnetic fields is a considerable distance from the object being analyzed.; The Near-Far-Near (NFN) FDTD method eliminates the intermediate space between the source and the target object. Instead of using a direct FDTD calculation, it computes the fields using a collection of plane waves. Calculating the plane waves requires considerably less computer memory and computation time than using traditional FDTD to calculate the fields. For practical problems, a ground plane is normally present in the intermediate region. This ground plane was originally calculated by simply using a perfect electric conductor (PEC). However, greater accuracy requires the introduction of a ground plane of arbitrary permittivity and conductivity. The approach presented here utilizes the original NFN-FDTD method with a PEC ground plane and modifies it so that a more accurate ground plane is used. (Abstract shortened by UMI.)...