Rational functions and other techniques for RF and microwave modeling

This thesis contributes several techniques for electromagnetic-based computer-aided modeling of microwave components exploiting rational functions, space mapping, Finite Difference Time-Domain (FDTD) method etc. First, enhanced adaptive sampling algorithms, both in single and multi-dimensions, are proposed. The algorithms are based on rational interpolation, which leads to more accurate high-frequency models as compared to other existing interpolants, e.g. spline. Starting with a minimal number of support points, i.e. electromagnetic data, and with lowest-order rational functions, the algorithms systematically produce models, which meet user-specified accuracies. In each stage of these algorithms new support points are adaptively selected based on model errors. The advantages of the proposed algorithms are shown through practical RF and microwave examples. Second, a new space-mapping based CAD methodology for modeling temperature characteristics of combline resonators is proposed. With the aid of two commercial simulation tools, namely Ansoft's HFSS and Agilent's ADS, this methodology gener ates accurate temperature models of combline resonators. The method is generic i.e. it is capable of generating corresponding models for a variety of resonator structures including the mushroom and straight. The model generated using space mapping is suitable for compensation methods where the type of material to be used has yet to be determined. Third, a FDTD based technique, integrated with rational functions has been developed to generate fast and accurate temperature models for combline resonators. Through examples, it has been shown that a FDTD algorithm with 2D uniform-grid distribution is fully capable of modeling temperature behavior of combline resonators. The advantage of this work over other numerical solutions in terms of computational complicity and required simulation time is illustrated. This technique can be applied to compensation methods requiring geometry optimization