Computer Aided Design of Wide-Band Microwave Components

Title of dissertation: Computer Aided Design of Wide-Band Microwave Components Mohamed Fahmi, Doctor of Philosophy, 2007 Dissertation directed by: Professor Kawthar A. Zaki Department of Electrical and Computer Engineering In recent years there was a notable developmental leap in communications systems operating at microwave frequencies. Such development was necessary to support a wide variety of emerging applications. Microwave communications systems can be found in many services such as satellite television and radar systems for civilian and military uses. Examples of such systems may include direct broadcast satellite (DBS) television, personal communications systems (PCSs), wireless local area networks (WLANs), global positioning systems (GPSs) as well as the 3G cellular services, which were designed for access to the Internet and to provide wide bandwidth applications. In the dissertation, the goal is to demonstrate the challenges and to propose solutions that enable the successful design and realization of very wide band microwave components, in particular, microwave directional couplers and lters. Such components are essential for development of modern communications and radar system operating at microwave frequencies. Directional couplers are an essential part in microwave systems. They are commonly used for dividing or combining signals. For example they are used in the generation of the desired power division in beam-forming networks for spacecraft antennas. In other applications, they are used for power monitoring. In the dissertation, a comprehensive treatment of wide-band ridge waveguide directional couplers is included. Analysis and design of di¤erent con gurations and arrangement of couplers realized in ridge waveguides are discussed. A new detailed systematic design procedure for ridge waveguide couplers in the two most used con gurations E-plane and H-plane is proposed. The procedure is based on extracting equivalent circuit parameters of a building block from full electromagnetic wave simulation, and then assembling multiple units to realize higher order couplers. Filters are also an integral part of any communication system. They separate communication channels operating at di¤erent frequencies thus eliminating interference between di¤erent channels. In the dissertation, design issues of wideband ridge waveguide elliptic function lters realized in Low Temperature Co- red Ceramics (LTCC) are discussed. Ridge waveguide lters have excellent characteristics such as wide stop-band and compact size. An excellent approach in manufacturing RF/microwave systems is the integration of components into multilayer substrates using LTCC which facilitates the design of microwave modules in the same package thus increasing reliability and reducing size. A new scheme to achieve the strong couplings, a crucial requirement for the realization of wide band elliptic lters is proposed in the dissertation. As an example, rigorous mode matching method is successfully used in the analysis and design of a challenging wide-band ridge waveguide lter realized in LTCC technology. Another interesting realization of couplers is the realization in strip-line transmission lines. In the dissertation, new proposed multi-section multi-layer LTCC stripline couplers are designed and analyzed. The proposed design enables the designer to achieve precise performance otherwise restricted by limitations posed by available technologies. The realization of wideband performance is made possible by such proposed design. Computer Aided Design of Wide-Band Microwave Components