The Application Of The Multilevel Characteristic Basis Function And Its Improved Technology In Electromagnetic Scattering Problems

The analysis of electromagnetic scattering characteristics problem from targets has an important influence on the design of the radar system,research of target stealth and anti-stealth technology and research of target recognition based on radar echo signal.The data of electromagnetic scattering characteristics from targets can be obtained by measurement.However,the measurement requires expensive measurement equipment,the ideal measurement environment,and need to spend a lot of manpower,material and financial resources.It also requires a longer test cycle.In contrast,it is more convenient and lower cost to analyze electromagnetic scattering problems by using the theoretical modeling and numerical simulation.Therefore,how to analyze the electrically large scattering problems accurately and efficiently has always been a hot topic in computational electromagnetics.In this context,closely around the two key issues of improving the calculation precision and efficiency,the research on the application of the multilevel characteristic basis function method(MLCBFM)which based on method of moment(MoM)and the improved technology in electromagnetic scattering problems have been studied.The research in this dissertation has been mainly divided into two parts.From the point of view the two questions about computational efficiency and accuracy,the research on the MLCBFM and the improved technology has been studied in the first part.The second part is extending the application of the CBFM,the reconstructed CBFM has been applied to the analysis of electromagnetic scattering characteristics over multi incident angles from conducting targets.In the first part,for the electrically large scattering problems,it is unfortunate that the number of unknowns per block increased in order to keep low number of blocks.It directly makes the characteristic basis functions(CBFs)generation procedure increasingly expensive in time and storage consumption.To mitigate this problem,a multilevel version to the CBFM called the MLCBFM has been presented first.Meanwhile,the adaptive cross approximation(ACA)algorithm is used for two levels CBFs efficient generation and reduced matrix fast calculation.Numerical results are given to demonstrate the accuracy,efficiency and the reduction of memory requirement of this method.Afterwards,a fast and accurate hybrid approach based on the MLCBFM is presented.In the hybrid method,a modified fast dipole method(MFDM)is proposed to improve the accuracy and efficiency of the conventional fast dipole method(FDM).Then,the MFDM is combined with the adaptive cross approximation(ACA)algorithm and the equivalent dipole method(EDM)to enhance the efficiency of the MLCBFM.In the proposed hybrid method,the use of MFDM makes the construction of secondary characteristic basis functions(SCBFs)and reduced matrix of the MLCBFM more accurate and efficient.The impedance matrices representing the interactions of the middle-field pairs are efficiently compressed by using the ACA in order to enable the hybrid method to further reduce the time and the memory significantly when the criterion for the far-field pairs becomes stricter to obtain relatively high accurate solutions.The numerical results of have demonstrated that the MFDM is capable of effectively reducing the CPU time and the relative errors.It has also shown that the proposed hybrid method has reduced the CPU time and the memory requirement when the same criterion for the far-field pairs is chosen.In the second part,a merged characteristic basis function method(MCBFM)is proposed to analyze the electromagnetic scattering characteristic from conducting targets.First,an improved primary CBFs(PCBFs)is newly defined.The mutual interaction of surrounding blocks is taken into account in the PCBFs.Discarding the first order secondary CBFs,then the high order CBFs are used to enhance the accuracy of the previous results.Because the interaction of surrounding blocks is fully considered in each CBF,the high precise results can be obtained with requiring only a small number of incident plane waves by using the MCBFM.The numerical results have demonstrated that the improvement of accuracy and the efficiency are both achieved by the proposed method.A summary and analysis of the improvement of the MLCBFM has been made in the end of the dissertation.And the future research work has also been prospected.