Research On Fast Algorithms For Wide-angle And Broadband Electromagnetic Characteristics Of Complex Targets

In the electromagnetic compatibility(EMC)analysis,the stealth and anti-stealth design and the array antenna optimization etc.,wide-angle(multi-incident angle)and broadband electromagnetic(EM)scatterings of complex target are of great engineering significance.Compared with the Method of Moment(Mo M),the integral equation(IE)based multilevel fast multipole algorithm(MLFMA)shows higher computational efficiency in calculating the accurate EM scattering of electrically large metallic target at a single incident angle or single frequency.However,when calculating the wide-angle and broadband EM scatterings point by point,MLFMA will require a large amount of computational time.Especially,when analyzing the broadband EM scattering of complex dielectric-metallic object,MLFMA is difficult to obtain EM scattering solutions in a wide frequency band due to the bad matrix condition number,the local high-unknown density and the low-frequency breakdown.In view of the low-frequency breakdown limitation and the low point-wise computational efficinency of MLFMA,several important research works are proposed in this dissertation.(1)For the EM scattering of electrically large and multi-scale metallic target,the low-order surface integral equation(LOSIE)based multilevel accelerated Cartesian expansion(MLACE)method is stdudied and implemented.And then,by combining the MLACE and MLFMA,a hybrid fast algorithm(MLACE-MLFMA)is presented,which shows better performance in calculating wideband EM scattering.Moreover,the highorder surface hierarchical vector basis function(HVBF)based MLACE-MLFMA is studied,which could obtain a more wideband EM scattering point by point only by changing the order of HVBF rather than replicable meshing.(2)For the EM simulation of hybrid inhomogeneous dielectric-metallic complex object,the low-order volume surface integral equation(LOVSIE)based MLFMA,MLACE and MLACE-MLFMA are stdudied and implemented.In addition,the high-order volume and surface HVBF based MLACE-MLFMA is also presented in this thesis.The higher-order MLACE-MLFMA can still calculate the EM scattering in a broader frequency band point by point only by changing the order of HVBF rather than replicable meshing.Compared with the low-order MLACE-MLFMA,high-order MLACE-MLFMA can largely reduce the memory cost.(3)Based on the low-order SIE-MLACE-MLFMA,a novel accurate and fast reduced basis method(MLACE-MLFMA-RBM)is proposed.In the MLAE-MLFMARBM,the increasing number of samplings will not deteriorate the interpolation accuracy.On the contrary,the more samples,the higher the interpolation accuracy.And,in the whole interpolation process,there is no need to store the Taylor expansion order related impedance matrices,which can significantly reduce the memory cost.Moreover,in order to determine a relatively complete orthogonal subspace for MLACE-MLACERBM,a novel adaptive sampling algorithm(ASM)is also proposed.(4)Based on the low-order VSIE-MLACE-MLFMA,a novel accurate and fast VSIE-RBM interpolation method is proposed.Meanwhile,by combining the VSIERBM and a novel adaptive segmented strategy(ASS),an adaptive segmented interpolation method(VSIE-ASRBM)is also presented.Compared with VSIE-RBM,VSIE-ASRBM has higher broadband interpolation efficiency.In addition,based on the high-order VSIE-MLACE-MLFMA,a novel HOVSIE-RBM is proposed.Compared with VSIE-RBM and VSIE-ASRBM,HOVSIE-RBM further reduces the interpolation memory consumption,and obtains a higher wideband interpolation efficiency.(5)By combining the MLACE-MLFMA and a simple overlapping domain decomposition method(SODDM),a high-order hierarchical vector basis function(HVBF)based novel fast simple domain decomposition method,i.e.SODDM-HOVSIE,is presented.SODDM-HOVSIE could effectively improve the iterative convergence of the high-order VSIE-MLACE-MLFMA,further reduce the memory cost,and be a good candidate for calculating RBM samples of complex targets.