Hybrid Methods For Analysis Of Electromagnetic Scattering And Its Related Problems

Evaluation of electromagnetic scattering by complex objects may be of interest in many military and civil areas. In this dissertation, several kinds of hybrid techniques that combine some high-frequency techniques with low-frequency methods are proposed to deal with this problem. Main efforts are put on the computation of scattering by electrically large bodies with small cracks and cavities on their surfaces. Besides, some related problems such as scattering from cavities and slits in a conducting plane are also investigated. The hybrid techniques in this paper provide efficient and accurate means for the analysis of scattering problems that can be effectively treated neither by a high- frequency technique nor by a low-frequency method alone. The author抯 main contributions are as follows: 1. The generalized network formulation is employed to the analysis of scattering by complex objects for the first time. Based on this, several hybrid methods including LPO-MoM, IPO-BIM and IIPO-FDTD are developed. The high-frequency asymptotic method and the low-frequency numerical method are combined in such a manner that 1) it permits the two kinds of methods to be used separately and ii) it includes all significant interactions. General programs based on the hybrid techniques are developed and the coupling effects for a complex object on its scattering properties are investigated. These couplings include those between different parts of the large body itself, the large body and the small cavities and different parts of the small cavities. This work provides a basis for the optimization of the RCS of the complex targets. 2. The electromagnetic scattering by arbitrary cavities in a conducting plane is investigated by using the generalized network formulation and the connection scheme. Some examples including those containing complex terminations are presented, demonstrating the accuracy, efficiency, and capability of the technique. One significant advantage of this technique lays in the fact that the cavity can be split into sections using the connection scheme. The network representations of some common sections can be precomputed and stored for later use. So the scheme is well suited to serve as a computer-aided design tool for cavity scattering problems. 3. A new technique for extracting the admittance matrix of a crack or a cavity from its equivalent aperture magnetic currents is proposed. For a crack or a cavity with complex geometry, it seems feasible to use the FDTD method to compute its admittance matrix directly. However, this results in a slow-convergent and unstable solution due to 1/~~ the multiple reflections inside the cavity. In this dissertation, we first compute the equivalent aperture currents of the cavity under various excitations with the aperture opened and then the generalized network representation of the crack is obtained by using equation transformations. Thus the drawback of the former method is efficiently overcome. 4. A new technique that combines the generalized network formulation along with the boundary integral method and the connection algorithm is proposed to analyze the electromagnetic coupling through a complex three-dimensional slot in a conducting plane. This technique, in particular the usage of connection algorithm, can not only efficiently handle arbitrary slots regardless of their geometry and material properties but also greatly...