Study On Wide-Band Electromagnetic Scattering Characteristics Of Target On The Ground

With the development of detection technique in battlefield, the detection and resolution have become important development directions for target, especially concealed target on the ground. At present the wideband low frequency scattering research of target on the ground is at the developing stage and lacks the general research. Based on the scattering problem that the target is on the ground, this dissertation is to investigate the wideband low frequency electromagnetic scattering characteristics of target at three parts: simulation algorithm for dispersive media, the scattering modeling method of target on the ground and measurement method.Among the lots of electromagnetic scattering simulation methods, the finite difference time domain method (FDTD) is chosen as the primary prediction method because FDTD has advantage in wideband problems. The FDTD must be treated especially for dispersive media. Several FDTD and perfectly matched layers (PML) for dispersive media are introduced and base on them a versatile FDTD program on C language platform is developed for the wideband scattering calculation of target on the ground.Aimed at some novel time domain algorithms, the research works are carried out.The pseudo spectral time domain method (PSTD) is a kind of high order accuracy method. Theoretically the wideband scattering results can be obtained accurately when one wavelength is divided into two cells. It is verified that PSTD can simulate the scattering problem of electric large target. The reduced finite-difference time-domain method (R-FDTD) can theoretically reduce 33% memory requirement in the storage of field components. PSTD method is combined with R-FDTD and a new method R-PSTD is proposed. The R-PSTD can reduce 25% memory requirement than PSTD and improve the simulation ability for scattering problem of electric large target farther.Alternating direction implicit (ADI) FDTD method is an unconditionally stable time domain algorithm. The maximum time step size is not limited by the CFL condition, but rather by numerical errors. Compared with the conventional FDTD method, the time step size of ADI-FDTD can be much larger, so it takes less time to simulate. The 3D stability demonstration is derived and corrects these errors in literature. The ADI-FDTD is used to simulate 3D scattering problem for the first time and some pivotal techniques are obtained. Then the ADI-FDTD is extended to 2D and 3D dispersive media and detailed formulations are derived. The modified Berenger PML formulations for dispersive media ADI-FDTD are also derive similarly.For improving the accuracy of simulating the scattering of target on the ground, the taper incident wave is used instead of uniform incident wave and reduces the diffraction produced by the ground truncation edges. 2D random rough surface is applied for the first time in FDTD simulation and the method how to generate the 2D surface is proposed. When simulate the scattering of target on the ground, an efficient method introducing the incident wave is proposed. After analyses the composition of scattering of target on the ground and based on the composite exciting method, a modified composite exciting method is proposed and can save a lot of memory requirement.Using above method, the scattering of cube and cylinder on the ground are simulated. Compare with MOM results in literature agreements can be observed. Then the wideband multi-polar and multi-angle backward and bistatic scattering of several simple geometries are simulated. Aimed to complex structure target, a new meshing technique based on facet models was introduced. Using this technique, one can mesh most of the target models and need not to care about what file format they use or where they come from. One meshes and simulates the wideband multi-polar and multi-angle backward and bistatic scattering of M1A1 tank, truck and missile launcher.At last one analyses the feasibility of indoor scattering measurement and propose a scheme that can measure the scattering of target on the truncated ground indoors. Using the scheme, the backward scattering measurements are taken for several ground materials and targets at 1.8GHz-5.8GHz. The ground materials include sand, clay and concrete. The targets include PEC cube and cylinder. The simulation results are compared with the measurement results and agreements are observed when the incident wave is almost perpendicular to the ground surface. The validity of algorithm and modeling is further verified.