Study And Application Of Fast Multipole Method In Complex Electromagnetic Environments

On research of complex and electrically large airborne and shipborne platforms, the analysis of radiation characteristics of antennas and electromagnetic compatibility (EMC) of multiple-antenna system has been a difficult issue in electromagnetic (EM) engineering area. In addition, in fields of high performance antenna design, radar stealth and anti-stealth technology research, radar system design and radar target identification and modern electric systems'EMC analysis, it is necessary to simulate the EM characteristics of some electrically large objects which are composite of complex structures. To fulfill these engineering requirements, the author selects the following as the investigating objects: the EM scattering and radiation problems of electrically large complex metallic structures and the EMC analysis of multiple-antenna system on electrically large platforms, which aims at efficiently modeling and fast computing the EM characteristics of electrically large complex structures, and finally solving some difficult engineering problems. In the process of researching, electromagnetic surface integral equation (SIE) theory is chosen as the theoretical foundation, and the multilevel fast multipole algorithm (MLFMA) based on the traditional method of moments (MoM) is utilized to accelerate the solving process and reduce the memory requirement. Two kinds of EM problems are dealt in this dissertation, one is the EM radiation and coupling problems on the structure of antennas, and the other is the radar scattering and wideband time-domain (TD) response of electrically large objects.In the research of EM radiation and coupling problems, the author sets the surface-wire structure as the main model, introduces the three types of basis functions for surface-wire structure, and discusses the MoM procedure for surface-wire model in detail. In addition, the MLFMA is employed to solve the electrically large problems with high efficiency. To improve further the solving efficiency, the solution to the near-field matrix equation is chosen as the initial guess for single frequency simulation, and the inherited iterative method is used for multiple-frequency simulation. Meanwhile, the author designs a physical-based preconditioner which only considers the most important contribution to the near field. With a simple conformation, the preconditioner can accelerate effectively the convergence rate of conjugate gradient (CG) type iterative solvers.On the problem of scattering, the author defines the scattering matrix in frequency domain (FD) according to the analysis of EM scattering characteristics. The matrix depends on the scattering geometry, the frequency, the angles of the incident plane wave and the scattering angles. To obtain the ultra-wideband (UWB) time-domain scattering characteristics, the numerical techniques based on the frequency-domain integral equations are firstly resorted to achieve the frequency-domain results, and then the results are transformed to the time domain utilizing the inverse Fourier transform, implemented as an inverse Fast Fourier Transform (IFFT). To describe the ultra-wideband time-domain response, the normalized time-domain response matrix is defined, and it depends on the angles of the incident plane wave and the scattering angles, similar to the scattering matrix aforementioned.Furthermore, considering the influence of ground and seawater in real world, the author makes a further study on the half-space MLFMA. The near interactions are evaluated via the use of the exact dyadic Green's function as in the half-space MoM; the"direct"terms of far interactions (as if the target was situated in a homogeneous medium) are evaluated via the free-space MLFMA, with only minor changes due to the lossy background; the"reflected"terms of far interactions are evaluated via the real-image method, which is clear in physical concept, and favorable in convergence and stabilization. There is only one set of real image clusters in real-image method, as opposed to multiple complex image locations required in the discrete complex-image technique (DCIT). This property reduces the overall CPU and memory requirements significantly.There are many EM scattering and radiation problems which require huge computation resources, such as the EMC analysis of airborne and shipborne multiple-antenna system. It is necessary to use parallel computation to improve computing efficiency and enlarge computing scale. Therefore, the author implements the parallel multilevel fast multipole algorithm based on OpenMP software and multi-core hardware environment. The parallel method is easy to realized, and the parallel efficiency is higher than the available codes utilizing message passing interface (MPI). What's more, the author analyses several EM scattering and radiation problems about formations of aircraft and ship with the parallel algorithms as engineering instances to back the research. Numerical results in this dissertation can be offered as valuable references for electromagnetic engineering.