Research On Algorithms And Characteristics Simulation Of Electromagnetic Scattering From Complex Target

As one of the key techniques in radar counterwork, the radar cross section (RCS) reduction is of great significance in military fields. Coating the outer surface of conducting target with radar absorbing thin-layer dielectric, can not only weaken the electromagnetic energy scattering from the target, but also redistribute the scattering electromagnetic waves to the uncaring direction, which has become a pursued goal in electromagnetic stealth field for complex target. The research on the electromagnetic scattering of conducting target coated with thin-layer dielectric, as a topic of great value in computational electromagnetics, has a wide range of applications in the fields of radar detection, electromagnetic wave propagation, as well as high-frequency antenna design, and become of great concern in the field of radar anti-stealth, which has broad application prospects in electronic countermeasures. Conducting object coated with thin-layer dielectric is equivalent to impedance surfaces with no thickness using impedance boundary condition, with the relationship between tangential electric field and magnetic field vectors given by a surface impedance dyadic. The external electromagnetic field scattered from the thin-layer dielectric coating object can be calculated with no need to investigate the distribution of the internal field, which can avoid some difficult problems such as the derivation and calculation of the Green’s function for the composite target. Furthermore, the unknowns can be greatly limited to the outer surface of the coated conductor, and then surface electromagnetic fields integral formulas can be used to efficiently explore the electromagnetic scattering, thus simplifying the procedure of analysis and numerical solving for electromagnetic scattering from complex structures.The research on electromagnetic scattering algorithms and characteristics simulation for thin-layer dielectric coating object of different electrical size, based on the impedance boundary condition is performed in this paper. For the case of small electrical size, method of moments(MoM) is presented respectively for the electromagnetic scattering from two-dimensional anisotropic inhomogeneous impedance cylinder of arbitrary section shape and three-dimensional arbitrary conducting object coated with dielectric. Exact integration to calculate the interaction between surface triangular facets is needed in three-dimensional MoM solution, which may result in low efficiency. Multi-layer UV decomposition technique is adopted to reduce the computer memory requirements and computation time by reducing the complexity of the matrix-vector multiplication in iterative solution, in order to effectively improve the computational efficiency and broaden its range of application; For the case of large electrical size, the total electromagnetic scattering is divided into the dominant contribution of surface scattering and the secondary contribution of edge diffraction. The double-bounce physical optics (PO) algorithm is applied to obtain the surface scattering contribution. With the help of uniform geometrical theory of diffraction (UTD) solution by impedance wedge with arbitrary exterior wedge angle at arbitrary skew incidence, the incremental length diffraction coefficients (ILDC) or equivalent edge current (EEC) for finite edge can be derived, in order to improve the physical optics field with fringe wave contribution, to implement the high-frequency estimation of electromagnetic scattering from electrically large conducting object coated with dielectric; For the case of dielectric coating conducting target of medium electrical size, a MoM-PO hybrid method is presented for the electromagnetic scattering. In addition, the electromagnetic scattering and radar image of ground/maritime targets are performed based on the proposed various algorithms, which may provide theoretical guidance and database support, to improve the theoretical research for target characteristics and radar systems. The main content of this paper includes the following parts:1) The electromagnetic scattering from electrically small conducting object coated with dielectric is studied by the MoM algorithm, respectively for the scattering from two-dimensional anisotropic inhomogeneous impedance cylinder of arbitrary section shape and three-dimensional arbitrary conducting object coated with dielectric. Multi-layer UV decomposition technique is adopted to accelerate the MoM algorithm for conducting object coated with dielectric.2) The electromagnetic scattering from electrically large conducting object coated with dielectric is studied by the high frequency algorithm, including the double-bounce PO method for impedance surface, as well as the ILDC for finite impedance edge.3) The electromagnetic scattering from electrically medium conducting object coated with dielectric is studied by the MoM-PO hybrid method. The discontinuous, geometrically complicated parts or the part with a rapid change in curvature, such as edges or corners will be grouped into the MoM-region generally, while the left continuous, smooth parts will be grouped into the PO-region. Then the total scattering fields can be equivalent to the radiation of electric or magnetic current in the MoM-and the PO-region.4) The high frequency scattering characteristic and radar image of ground/maritime targets are studied. The electromagnetic simulation of composite scattering from targets and the land/sea environment are performed by the PO-EEC algorithm, in order to obtain the RCS, high resolution range profiles (HRRP) and2-D spotlight synthetic aperture radar (SAR) image.