The Analysis Of Near-field EM Scattering From Targets By Moment Methods

Increased importance has been attached to the near-field EM scattering characteristic of targets and the near-field EM scattering characteristic of targets is a very complex physical process because it ranged over many factors. It is too difficult and complicated in contrast with the far-field.The main research work in this dissertation involves the fallowings:(1) The standards of division are classified. To describe the properties of EM scattering by objects, the concept of GRCS(Generalized Radar Cross Section) has more practical meaning especially. Three models are set up. The near-field EM scattering characteristic of conducting targets is researched. In this paper. An important principle ofelectromagnetic field theory------reciprocity principle is introduced. The RWG vectorbase functions are used to denote inductive current on the surface of conducting target. EFIE is built. The GRCS of conducting sphere, conducting plate, conducting cube are calculated respectively under the three models.(2) The dielectric targets' near-field electromagnetic scattering is researched.Another important principle of electromagnetic field theory ------equivalent theory isintroduced. Different from the conducting target, there has not only equivalent electric current but also has equivalent magnetic current on the surface of dielectric target. So now should built two equations—EFIE and MFIE to obtain the unknown current coefficients. The GRCS of dielectric sphere, dielectric plate and dielectric cube are calculated respectively.(3) Finally, the coat targets' near-field electromagnetic scattering is researched. Two cases are analyzed: conducting target with coat and dielectric target with coat. For the former, there have equivalent electric current and magnetic current on the surface of conducting object. The RWG vector base functions are used to denote equivalent electric current and magnetic current. Now three equations integral equation should to be built to obtain the unknown current coefficients;for the latter, there have equivalent electric current and magnetic cunent not only on the surface of coat but also on the surface of dielectric object. So, four equations should be built to obtain the unknown current coefficients.The method of this paper can't be used to calculate electric-big size targets, because there will be much more units in the matrix, and all these are limited by the speed and memory of computer. The MoM is to be in conjunction with other methods, such as high-frequency, to increase the speed, to extend the field of using.