Novel Planar Microstrip and Dielectric Resonator Filters
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Microwave filters possessing various forms are essential components in radar, satellite, and mobile communication systems. Increased demands for low-loss, miniature filters that can be mass produced at low cost have provided a significant challenge reinforcing the need for improving or even replacing the conventional microwave filters. In recent years, the concept of Photonic/Electromagnetic Bandgap (PBG/EBG) structures has attracted the attention of the microwave engineering community. The main feature of PBG/EBG structures is the existence of a bandgap in the frequency spectrum of a propagating photonic/electromagnetic wave. The motivation for adopting EBG structures stems from their capability to eliminate unwanted wave propagations in various microwave devices. This thesis investigates and proposes novel planar microstrip filters employing EBG structures in the form of slots etched on the ground plane. Such filters are not only compact, but also can improve the RF performance in both the passband and the stopband. This proposed concept is further extended to implement low-loss tunable lowpass filters, both digital and analogue, by integrating tuning elements directly into the slots. Transmission line circuit models are developed to design the proposed microstrip filters and tunable lowpass filters. To verify the concept and the validity of the developed circuit models, theoretical and experimental results are presented and carefully compared. Currently, dielectric resonator (DR) filters have been widely employed in wireless and satellite communication systems. Over the past two decades, tremendous progress has been made to reduce the size, and enhance the in-band and out-of-band performance of DR filters. However, the current approaches for implementing DR filters are relatively expensive and hardly amenable to mass production. Cost reduction remains a key limiting factor that needs to be addressed now. A new configuration of DR filters is presented in this thesis. The novel concept simplifies the assembly, integration, and alignment of DR filters, significantly reducing production time and costs. Not only is the design of the proposed multi-pole DR filters and diplexers examined, but also the fabrication technique. The experimental measurement results confirm the validity of the theoretical designs of the new filters, which makes this concept very attractive for further applications in both wireless and satellite communication.