Research On The Electrically Large Radiation And Scattering Problems In Electromagnetic Fields

In this paper, the electrically large electromagnetic problems as the research objects, using the parallel computation technique and the fast algorithm, some research work is done to analyze the radiation and scattering problems in the free space and multilayered media respectively.On the foundation of the Method of Moment, the parallel MoM is given in this paper at first, and the electrically large problems are analyzed primarily. To analyze the scattering and radiation problem of the surface/surface junction structure electrical large structure in free space, the method to deal with the junction is presented. For the scattering problem, using this model to simulate the targets with no thickness junction plane instead of thin plane, the number of unknowns and the memory could be reduced greatly. For the antenna problem of probes excited, the wire/surface model can be equivalent to the surface/surface model using the thin strip structure to simulate probes or dipoles. The uniform basis function can be used in this model and no need to introduce a special basis function to the junction. So it is more suitable for the MLFMA analysis. For increasing the solution speed of radiation problem using multilevel fast multipole algorithm, a novel pre-corrected method is presented in this paper. It generated a small impedance matrix in the local region near the feed point and evaluates the local surface current, which could approximately describe the characteristic near the excited point. The difference between unknown and the local current approaches the zero vector more than unknown current itself. So it needs less iteration using the difference as the unknown vector to get the solution.For the problems in multilayered media, the Green's functions of the electrical dipole and magnetic dipole lying in the multilayered media are given and calculated by the two level approximations discrete complex image method. So the Green's functions can be written as the closed forms. Using them in MoM, we analyzed the planar microstrip circuits at first and extract the network parameters of the circuits. Together with network analysis method, the microstrip circuits with via grounding structures are analyzed. Replacing the via grounding structures and substituting the edge ports for them, the original circuits could be equivalent to the generalized multiport models with only planar structure. Basing on the planar microstrip circuits, the enclosed microstrip structure is analyzed and the package effects are removed by modifying the impedance matrix by the images theory. And then using the parallel MoM in multilayered media, the large scale microstrip patch array antenna is analyzed. As a special case of the multilayered media, the electromagnetic scattering characteristic from the 3D conducting object above the random ocean-like rough surfaces is also evaluated. The water sea could be regarded as the half low space medium and the sea rough surfaces could be regarded as the dielectric surfaces above the sea. The scattering characteristic of this model is calculated by establishing the integral equation of the combined conducting/dielectric objects and solving the matrix equation with the iteration method.