Thesis (MScIng)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Th.--Électronique--Toulouse--I.N.P., 1984. N°: 85.

In this dissertation, a variety of semiconductor based transmission lines are investigated. Among them are metal-insulator-semiconductor (MIS) coplanar waveguide (CPW) slow-wave structures and laser diodes. Although laser diodes are electro-optic devices, their microwave parameters are of great importance for broadband matching to their driver networks. It will be shown that, besides their optical characteristics, laser diodes can be regarded as bias-dependent lossy and dispersive slow-wave transmission lines for the driving RF/microwave signal. The analysis of this kind of transmission lines is very difficult or even impossible through a single numerical approach. Therefore, in this thesis a combination of two methods is applied, namely, the complex finite difference method (CFDM) and the frequency-domain transmission line matrix (FDTLM) method. The CFDM provides a self-consistent solution to the semiconductor equations, which determines the conductivity distribution in the semiconductor layer as a function of the bias current. The FDTLM method utilizes this information to calculate the microwave characteristics of such a multilayered, lossy transmission line. The development of the CFDM, based on information available from the literature, is described in detail. For the FDTLM method, an investigation is presented analyzing the errors of the various node representations. On the basis of this investigation, a new node, the hybrid node with shunt decomposition, is developed. This node shows better accuracy than other nodes and is particularly well suited for the analysis of lossy, semiconductor-based structures. Furthermore, by using finite differencing and averaging, the theoretical foundation of the FDTLM method is expanded and, for the first time, a direct relationship between the electromagnetic field and the voltages and currents in the hybrid node with shunt decomposition is established. On the basis of the numerical techniques developed in the first part of the thesis, mode propagation and scattering of electromagnetic field in a variety of semiconductor-based structures are investigated. Besides the microwave effects in semiconductor lasers and the slow-wave characteristics in MIS CPW structures, the second part of this thesis concentrates on the scattering of fields at discontinuities between transmission lines. This includes wire bond and flip-chip transitions between transmission lines and laser diodes as well as direct transitions, for example, between slow-wave CPW structures on doped silicon and CPW on the same but an undoped substrate. Whenever possible, these results are compared with those from other methods and measurements. However, since most of the structures and transitions considered in this thesis are investigated for the first time, the data available in the open literature is limited. From the comparison of obtained results with the available data and measurements one can safely conclude that the numerical analysis presented for all structures is a true picture of the physical reality. / Graduate

RF/microwave terrestrial point-to-point and satellite communication systems employ a large number of waveguide components operating at microwave and millimeter wave frequencies. Accurate design of these components for optimum performance of the overall system is critical. To achieve this, computationally efficient and accurate numerical methods are indispensable tools in the design and optimization of components and subsystems. Among the large variety of potentially suitable numerical methods, the mode matching method in conjunction with the generalized scattering matrix technique has been found to be one of the most reliable and straightforward techniques to design waveguide components. In the past the method has been mainly applied to eigenvalue and scattering problems in rectangular waveguides. In this thesis, the mode matching method is extended to ridge waveguide problems in circular waveguides and thus closes a gap in the literature that has existed for a long time. The thesis begins with a study of the basic principles of the mode matching method as it is known from rectangular waveguides. These principles are then applied to the analysis of the rectangular ridged and coaxial waveguide, followed by an eigenvalue analysis of ridged circular waveguide. Rather than rectangular ridges, ridges of uniform angular thickness (conically shaped) are used in the circular waveguide to avoid a mixed coordinate system which would render the mode matching method computationally very inefficient. On the other hand, conically shaped ridges are as easy to fabricate as rectangular ridges and are not detrimental to the electrical performance of the component. The thesis then continues to treat the discontinuity problem at the interface between the empty circular waveguide and ridged circular waveguide. To verify the computed scattering parameters, measurements were performed and good agreement was found. By cascading several discontinuities transformers and evanescent mode filters were designed. A fifth order filter was designed and fabricated and also here good agreement between measured and computed data was found. The final chapter in the thesis analyses the coupling between orthogonal modes in the presence of an asymmetric discontinuity. Determining the coupling factor between orthogonal modes is an integral part of the design of polarizers and dual mode filters and for conically shaped ridges, has not been published in the open literature yet. To realize various coupling coefficients, a single or double ridges must be placed at an arbitrary angle to the exciting wave. The mode matching method is extended to include also this case and various convergence tests have been performed to validate the algorithm . As a final example, the algorithm has been applied to design a circular polarizer with two ridges. Although only two-port problems are treated in this thesis, the basic framework for the mode matching method in circular waveguide has been established and can now be extended to three-port problems. This will be the subject of future work to analyze and design power dividers and orthomode transducers. / Graduate

Im vorliegenden Beitrag untersuchen wir ausgewählte Formen der Orientierung im Kulturraum anhand der Textsorten Reiseführer und Audio-Guides. Die dafür herangezogenen Texte wenden sich an deutsche und nicht-deutsche Muttersprachler. Im Zentrum der Analyse stehen auf deutsch verfasste Texte, die Aspekte des Kulturraums im deutschsprachigen Gebiet behandeln; darüber hinaus haben wir aber auch Belege mit aufgenommen, die Kulturräume anderer Länder betreffen. Im Mittelpunkt steht bei der Analyse die Frage, wie Orientierung im Kulturraum erfolgt und wie durch ein derartiges Orientierungsangebot „kulturelles Wissen“ geformt wird, insbesondere bei Adressaten, die über dieses Wissen nicht, nicht in gleichem Umfang oder aber nicht mit der gleichen Fokussierung verfügen. Wir verstehen diese exemplarische Analyse als Vorarbeit für zukünftige, größer angelegte kontrastiv orientierte Projekte.

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