چكيده به لاتين
Due to the increasing of the various application of terahertz technology, the interest in using these waveguides is getting more and more popular due to their favorable propagation properties. Therefore, the analytical and accurate analysis of these structures is very important. For this purpose, the structure under study is considered to be two infinite uniform cylinders in z direction that their axes are positioned at a distance d from each other. In this thesis, given the dispersive modes (TM and TE modes) in the symmetric two-wire
waveguide; first, the Helmholtz equation is written in the bipolar coordinate system (BCS). After approximately solving the Helmholtz equation in this coordinate system, the characteristic equation obtained for the dispersive modes (TE, TM) had infinite results. Then, an optimal result has been achieved to maximize the difference between the roots of characteristic equation (In other words for maximizing the bandwidth), using the PSO algorithm. Also, the problem of the asymmetric two-wire waveguide is presented. The modal analysis of the structure is done using an analytical method. In this thesis, the solution of the TE and TM modes is done by potential formulation and an analytical expression is proposed for the electromagnetic fields and the cutoff wave numbers, the Items that there are not in any of previous works. In this study, for the first time a Bipolar Coordinate System has been used to formulate the two-wire waveguide problem and a direct method has been presented for solving the Helmholtz equation. The values of the cutoff wave numbers are calculated for the first few modes of TE and TM. Being fast, accurate and simple in implementation introduce the present method as an appropriate technique for analyzing the two-wire transmission line structures. Also In this study, the BCS is used for the first time to formulate the eccentric circular metallic waveguide problem and a direct method is presented for solving the Helmholtz equation. The values of the cutoff wave numbers for the first few modes are calculated and benchmarked. The precise correspondence of the values obtained with the previous studies and computer simulations, with the high speed and simplicity in implementation, introduces the present method as an appropriate option for analyzing eccentric circular cylindrical structures.
