Planar Leaky-Wave Antennas and Microwave Circuits by Practical Surface Wave Launching
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Modern communication systems have increased the need for creative antenna solutions and low-profile circuit configurations that can offer high-quality performance at a low cost. The microwave and millimeter-wave frequency ranges have shown much promise allowing for increased data transmission rates while also offering smaller and compact designs. Specific applications for these wireless systems include radar, biomedical sensors, phased arrays, and communication devices. Planar antennas and circuits are generally well adopted for these applications due to their low profile and ease of fabrication. However, classic feeding techniques for planar structures can be problematic. Losses can also be observed in these conventional feeding schemes due to unwanted surface wave (SW) excitation. This can lead to reduced antenna and circuit efficiencies, and thus, diminished system performance. It is shown in this thesis that by the use of planar SW sources, or surface-wave launchers (SWLs), innovative and efficient antennas and feed systems are possible. Theoretical analysis and experimental verification for these SWLs are initially presented. New topologies and array configurations are also examined for directive beam steering at end-fire and at broadside. Additionally, studied structures include novel surface-wave antennas (SWAs) and leaky-wave antennas (LWAs) for 3-D beam pattern control in the far-field. A comprehensive design strategy is also examined which describes the implementation of these planar antennas using SWLs. This design strategy is based on a full-wave analysis of the modes that can be supported by the planar structures which include various planar-periodic metallic strip configurations and partially reflecting surfaces (PRSs) or screens. With appropriate conditions SWs can also be bound and guided for field channeling and power routing. For instance, novel planar metallic SW lenses and guidance structures are developed. Demonstrated applications include couplers, transition sections, as well as new planar circuits for power dividing/combining. To the author's knowledge, similar techniques have not been previously studied in the literature which allow for such controlled SW propagation and radiation. This way, SWs, which are normally considered an unwanted effect are used here to advantage.