Razvoj i primena kompaktnog žičanog TLM modela za efikasnije projektovanje i analizu mikrotalasnih struktura cilindrične geometrije

Abstract

This thesis describes a development of the compact wire model and its implementation into the numerical TLM (Transmission Line-Matrix) method based on the cylindrical coordinate system for the purpose of modelling of cylindrical microwave structures containing wire elements. Presented approach overcomes possible uncertainty related to modelling of curved boundaries when the rectangular grid based TLM method is applied and limitations of the rectangular mesh particularly emphasized in the cylindrical structures containing wire elements and lossy loads. Consequently, a smaller number of TLM nodes is required contributing significant reductions in a memory storage and computer run-time in TLM simulations. Software implementation of the compact wire model into the cylindrical grid based TLM method resulted in the self-written code 3DTLMcyl_cw, which characteristics and possibilities are described in detail. Due to the cylindrical grid structure and an empirical nature of the compact model, its implementation has to take into account a change of wire parameters with a variable cross-section of the TLM nodes through which a radially placed wire conductor passes. For that purpose, an additional algorithm handling the connecting procedure for wire segments belonging to the TLM nodes with different cross-sections is developed. The corresponding non-commercial software based on the integral cylindrical TLM method is found to be a versatile tool which is ideally suited to the modelling of structures of cylindrical geometry. This is demonstrated on a number of examples which are divided in two categories: cylindrical cavity resonators as closed structures and microstrip circular patch antennas representing open problems. In the former case, a particular emphasis is placed on the possibility of modelling of radially placed probes with greater radius than the corresponding rectangular TLM mesh allows for. Also, a significant advantage of the developed solver is accentuated through the modeling of a coaxially placed dielectric used as a load of cylindrical cavity resonators. The latter category refers to the possibility of modelling of wire elements that are used as coaxial feeds, enabling prediction of the feed position in order to optimize the antenna’s performance. Besides accurate modeling of a circular radiating patch, it is shown that description of annular rings or narrow ring slots using the cylindrical mesh is straightforward compared to the rectangular grid based TLM method. In most examples considered in this thesis, numerical data are verified by comparison with measured results obtained from fabricated experimental models of cylindrical cavity resonators and circular patch antennas.