Analysis of Complex Microwave Structures Using Suitable Computational Electromagnetic Techniques

This thesis is concerned with the application of computational electromagnetics in the area of microwave engineering. Within the framework of this thesis, three-dimensional computational electromagnetic tools have been used for the modeling, characterization, and analysis of several microwave components. State-of-the art commercial electromagnetic simulation tools based on the finite integration technique and a non-commercial code based on the generalized multipole technique-mode matching technique hybrid method have been used for the computations. The commercial simulation tools have been applied to two real life complex applications, whereas the non-commercial code has been used for characterization of radiating apertures. In this context, some numerical techniques based on matrix decompositions to identify the redundant multipoles have been proposed to improve the generalized multipole technique-mode matching technique hybrid method. The first application is concerned with the third generation synchrotron radiation facility, PETRA III. Several components (the button type beam position monitors at two sections of the beam pipe, the longitudinal feedback cavity) of PETRA III have been extensively analyzed in terms of wakes, impedances, various loss and kick parameters and modal analysis. The effect of the ‘nose cones’ on the characteristics of the longitudinal feedback cavity, occurrence of trapped modes near the beam position monitor button have also been investigated in this context. The second application involves the modeling and analysis of an ultrawideband antenna for microwave communication. The complex shape of the antenna has been modeled and analyzed to identify the crucial parameters influencing the antenna characteristics. Based on this analysis and studies of the antenna, it can be adapted for several applications. An optimized version of the antenna has been presented along with the corresponding measurements. The third application is concerned with the characterization of radiating apertures using a hybrid method involving generalized multipole technique and mode matching technique. One of the crucial issues in this method is the multipole distribution along the antenna. Improperly placed multipoles, or presence of redundant multipoles, cause severe numerical instability leading to inaccurate results. Two algorithms to identify the redundant multipoles have been proposed and applied in the case of horn antennas with elliptical apertures. These algorithms are based on two well-known matrix decomposition methods. The effectiveness of both approaches have been validated by comparison of the actual boundary conditions with the computed ones. Additionally, comparisons between the far-field patterns obtained from a commercial finite integration technique software and the proposed hybrid method have also been presented.