Research On Modeling Algorithms Of Electromagnetic Scattering From Inhomogeneous Anisotropic Impedance Target

In recent years, the scattering by the perfectly conducting (PEC) targets coating with anisotropic dielectric has important engineering significance for various applications such as electromagnetic wave propagation, target characteristics, radar detection, electromagnetic compatibility, microwave remote sensing, electronic countermeasures and antenna radiation. The anisotropic dielectric coated on the outer surface of PEC target can not only absorb the electromagnetic energy of the incident wave, but also change the direction of the scattering waves to the uncaring radar detection direction by controling the optical axis direction of the dielectric, thus realizing the stealth of the target. As the impedance surface is widely used as an equivalent model for PEC surface coated with anisotropic dielectric medium, the PEC targets coating with anisotropic dielectric is equivalent as the anisotropic impedance target, the anisotropic dielectric is characterized by the surface impedance tensors. Because the surface impedance is relative to the incident direction and polarization of the incident wave, the surface impedances of different surface of the target are not consistent. This leads to the surface impedance of anisotropic impedance target is inhomogeneous. Moreover, the anisotropic dielectric coated on the target in practical engineering problems is generally inhomogeneous, which is equivalent to an inhomogeneous impedance surface. For instance, the ground surface composed by the rock, soil, forests can be only modeled by the inhomogeneous impedance surface. Therefore, it is essential and of great practical engineering interest to study the scattering by inhomogeneous anisotropic impedance targets.Based on the Leontovich impedance boundary condition, the research on electromagnetic scattering modeling methods for the electromagnetic scattering from inhomogeneous anisotropic impedance targets is investigated in this paper. The surface impedance tensor which is a function with position as the unknowns, constrains the tangential electric field and magnetic field on the target surface. Considering the scattering filed outside the target and ignoring the internal filed distribution, the unknows are limited on the surface of the target, and then surface electromagnetic fields integral equations can be applied to calculate the scattering field. For the two-dimensional inhomogeneous anisotropic impedance targets, the moment method (MM) is presented and the implementation of the MM is also detailed in the paper. For the three-dimensional inhomogeneous anisotropic impedance targets, the MM and the hybrid MM-physical optics (PO) are all applied for the sacttering of this type target.In additional, plane wave scattering by an infinite, three-dimensional wedge whose faces are characterized by periodic anisotropic impedances is investigated. An improved hybrid of the moment method (MM) and the physical optics (PO) corrected by the uniform geometrical theory of diffraction (UTD) is proposed to calculate the equivalent electric current on the wedge surface. The main content of this paper includes the following parts:1) The electromagnetic scattering from the two-dimensional inhomogeneous anisotropic impedance targets is studied by the MM algorithm. Using the surface current decomposition and the ray theory prediction, the connection between the simulated range profiles and the complex scattering mechanisms are established. The different order interactions give rise to different order range profiles. And the effect of the inhomogeneous anisotropic impedance on range profiles is discussed.2) The electromagnetic scattering from the three-dimensional inhomogeneous anisotropic impedance targets is studied by the MM algorithm and the MM-PO hybrid method. The computational burden may prevent the MM from being used for electrically large targets. The surface of the target is divided into an MM region and a PO region. The MM region occupies the discontinuous curvature region where the equivalent current varies fast and requires accurate modeling, while the region except the MM region is denoted as the PO region where the current varies slowly. Thus the unhnowns which requires accurate solving are reduced. Moreover, the UV decompose technology is introduced in the hybrid MM-PO method, and the computional complexity drops for both the memory requirement and the CPU time.3) The electromagnetic scattering from inhomogeneous anisotropic impedance wedges is studied. A hybrid MM-PO method combining UV technique is applied to calculate the electromagnetic scattering of a plane wave impinging on an infinite wedge with homogeneous anisotropic impedance faces. Plane wave scattering by an infinite wedge whose faces are characterized by the periodic anisotropic impedance is investigated. An improved hybrid MM-PO is developed to calculate the equivalent electric current on the wedge face. A periodic representation of the scattering face is used to prevent nonphysical edge effects in the scattering evaluation. Several universal series are derived for all elements of the interaction matrix in MM region, and the total current in PO region is the combination of the PO-current and the diffracted current.