A Study On The RCS Prediction Techniques In High Frequency For Complex Target Modeled With Nurbs Surface

From cold weapon war to the mechanization war, nowadays the information war age is coming. Each war will bring about changes in world pattern. How to improve the survivability of our military equipment under the radar detection? how to find the weakness of enemy’s weapon? They are all need to be supported by the electromagnetic properties analysis platform for the complex electrically large targets.In this dissertation, the analysis platform for scattering properties of complex electrically large targets is constructed with a good interface to computer aided design software (CADS), and the radar cross section (RCS) prediction of complex targets is realized.The interface module is constructed as the base layer for the platform to exchange data with CAD/CAM software. The electromagentic models in the platform are got in two access. The existing grid models and solid models are completed by reconstruction technique with point cloud data to get the parameters of non-uniform rational B-spline (NURBS). For the models designed by NURBS, the interface between RCS prediction software and CAD/CAM software is constructed by Initial Graphics Exchange Specification (IGES), which can be used in the modeling design adjustment of electrically large complex target with the CAD software.NURBS modeling is much better than traditional modeling method, however, because of the use of iterative method, the computing speed is limited. This dissertation changes the iterative top-down solution process to directive bottom-up process, the computing consume of NURBS modeing is greatly reduced. Such method is also extended to NURBS surface tangential vector, normal vector and the solution of two-order partial derivatives. By the given examples, the method and formulas are proved to be accurate.The physical optics method (PO) is used in the dissertation to complete the direct scattering computation of NURBS modeling. Because the shape parameters of the target is described in the NURBS, the scattering should be computed based on NURBS modeling techniques. The analysis platform in the dissertation completes the physical optics integrals based on NURBS modeling by using Ludwig integral. In order to correct the PO results, the edge diffraction field based on NURBS curved edge is computed by physical theory of diffraction (PTD). In the dissertation, the shadowing problem is also discussed in electromagnetic scattering computing. The Z-buffer technology in introduced to complete the shadowing process, and a assistant buffer is proposed to improve the traditional Z-Buffer technique in NURBS modeling.Cavity structure is a threat to the survival of military targets. Cavity for military targets is electrically large cavity in the general, and is often coated by dielectric layer. The dissertation analyze the scattering from cavity with shooting and bouncing ray method (SBR). The ray tracing and aperture integration features of rectangular cavity and cylindrical cavity commonly used as the military cavity targets are discussed in detail. The RCS formulas are derived with SBR, which can be used to calculate the perfectly electrically large conducting or coated rectangular cavity. It is proved by examples that such formula has the accuracy not less than the accuracy of original SBR method. At the same time, due to the adoption of the formula form to solve, the memory requirement and time consume are both reduced greatly. The dissertation gives a group of formulas for the characteristics of a cylindrical cavity to effectively predicte the ray tracing in a cavity, which save the original SBR ray-tracing consumption and computing time. For the more common terminated non-planar rectangular and cylindrical cavity, dissertation divides the solving region into regular cavity region and terminal region which molded in NURBS. The ray tracing in regular cavity is solved by formulas proposed in paper, and the ray-tracing of ray tracing in terminal region is completed by numerical methods. For more complex cavity, NURBS is used to describe the cavity, the numerical methods are used in ray tracing, field tracking and aperture surface integral.Electromagnetic modeling and scattering computation are gathered in the final part of the dissertation to be a complete scattering analysis platform for electrically large targets. By using the principle of locality of high-frequency field, the PO scattering and cavity scattering are combined to complete the RCS prediction of electrically large complex objects. The effectiveness of proposed analysis platform is verified by the experiment datas of an aircraft.