Improved Characteristic Basis Function Method And Its Applications In Electromagnetic Scattering Problem

The electromagnetic scattering of target is the information source of radar detection, geological surveying, and remote sensing. Analysis of electromagnetic scattering characteristics of these applications is the main basis for the design, operation, especially important in the characteristics analysis, identification of military objectives. The military objectives are usually some of the electrically large or complex targets. So how to obtain an accurate and efficient method for analyzing electromagnetic scattering problems is becoming a hot topic in computional electromagnetics. In this dissertation, we focused on the characteristic basis function method, which is one branch of method of moments, to reduce the memory requirements, enhance the computational efficiency in accelerating the characteristic basis function method and analyzing the wideband electromagnetic characteristics. The research of the characteristic basis function method in this dissertation divided into two parts, the first part is the improvement of the characteristic basis function method and acceleration technology. The second part is to expand the application of the characteristic basis function method to analysis of the wideband characteristics of targets.In the first part, the fast dipole method was presented to accelerate the matrix-vector products in the construction of characteristic basis functions and the calculation of the reduced matrix. The fast dipole method transforms the matrix-vector products of the far groups into aggregation-translation-disaggregation form naturally, so it can cut down the computational complexity and memory requirement. And then, an improved fast dipole method combined with the characteristic basis function method was presented to improve the computation accuracy and the efficiency of the conventional method. At last, we focus on the singular value decomposition-characteristic basis function method (SVD-CBFM), which should be set adequate plane waves in each sub-block to construct characteristic basis functions, thus increasing the number of characteristic basis functions and causing higher time consumption in singular value decomposition. An improved SVD-CBFM is presented. This approach reduces the number of plane waves and fully considers the mutual coupling effects among sub-blocks to obtain the secondary level characteristic basis function. Therefore, the total number of characteristic basis functions and the time required by singular value decomposition are significantly reduced. And also, the adaptive cross approximation algorithm is also used to accelerate the matrix-vector products in the construction of secondary level characteristic basis functions and vector-matrix-vector products in the calculation of the reduced matrix.In the second part, the characteristic basis function method applied into the analysis of the wideband electromagnetic scattering of the target was studied. Because the traditional ultra-wideband characteristic basis function method has the poor accuracy at the lower frequency points, so an improved ultra-wideband characteristic basis functions named general characteristic basis functions was presented. The general characteristic basis functions fully considers the mutual coupling effects among sub-blocks to obtain the secondary level characteristic basis functions, so it can improve the accuracy at the lower frequency points because the general characteristic basis functions contain more information of the current. Finally, a combination of general characteristic basis function method and model based parameter estimation technology was presented to reduce the frequency points, which only needs a small number of sampling points to fit the entire broadband RCS curve, so it can improve the computational efficiency.