Researches On Hybrid Methods For Electromagnetic Scattering By Cavity

The problem of calculating and reducing electromagnetic scattering by concave structures, such as jet inlet and exit of airplane, not only play an essential role in modern computational electromagnetic, but also are of special interest in certain military and defense application, because they usually cause strong radar echo and can be easily found. Different from closed structures, one part of the concave is usually exposed in the scattering field from the other part, so higher scattering is inevitable and cause the analysis more perplex. In this dissertation, different arithmetic is put forward to analyze such structures, and the main contents are as follows:1. The electromagnetic scattering mechanism of concave structure is studied systematically, and aiming at the problem when low-frequency numerical methods applied for electric large cave structure, a hybrid subsection method and wavelet analysis are proposed to reduce the operations.2. Ray-modal character is applied to reduce the large amount of modes in electric large waveguide, the computer operations are greatly reduced with keeping the solution precision.3. Hybrid modal method is proposed for analyzing open-ended cavities which ban be built up by jointing together subsections either be uniform waveguide or non-uniform sections, so that the general modal method became more flexible and widely used.4. Hybrid modal/Generalized Scattering Matrix(GSM) is applied to deal with the obstacle in the bottom of cavity. The characters of GSM are fully explored to dispose the multilevel obstacles, which are more alike the practical objects.5. Hybrid Iterative Physical Optics/Generalized Reciprocity Theorem (GRT) is proposed. In this method, Subsection avoids the large matrix and improved the shadowing judgment in the Iterative physical optics; Iteration improves the accuracy of high frequency method when they areuse to concave structure. GRT is introduced for two purposes: reduce the iteration and combining other methods.6. Spectral method is proposed to analyze cavity. The plane wave spectrum and physical optics are combined to analyze the EM wave propagation in arbitrary cavity. This method holds true for any source and arbitrary structure.