| Summary: | 博士 === 國立臺灣大學 === 電信工程學研究所 === 96 === This dissertation is focused on the development of microwave filters with wide bandwidth, compact size, sharp selectivity, broad rejection band, and easy design procedure, since the wideband systems have received much attention and most reported works on filters are principally concentrated on narrow bandwidth design. To facilitate the wideband filter design, the dual-metal-plane configurations are adopted for the proposed filters.
Firstly, the new coplanar waveguide (CPW) dual-mode filters are proposed based on the dual-metal-plane structure. In this work, to avoid bond wires, the elevated metal patches connected to CPW ground by metal vias are adopted as the air-bridge and also used as the shunt-capacitance perturbations. Besides, to achieve the large couplings required by the feeding scheme, the microstrip-to-CPW transitions are applied. By making good utilization of dual-metal-plane configurations, two dual-mode filters with 3-dB fractional bandwidth of 20.85 % and 31 % are designed and measured.
Secondly, the microstrip bandpass filters using new coupling scheme for achieving a large coupling are presented. By designing the connecting position associated with an admittance-inverter which connects two λ/4 stepped-impedance resonators, one may achieve the coupling of two resonators with a large amount. Moreover, including the conventional magnetic coupling structure can increase the design flexibility. In this study, three demonstrated microstrip four-pole filters with their bandwidth larger than 30 % are carefully designed and implemented to verify the proposed concept.
Thirdly, wideband bandpass filters based on both microstrip and CPW λ/4 resonators are fabricated. With the dual-plane layout capability and the cross coupling path, the tight coupling and two transmission zeros near the passband are effortlessly realized. Moreover, by designing the spiral-shaped inductors to form the miniaturized resonators, the filter may further be made compact. These fabricated filters possess not only good frequency selectivity but also compact sizes.
Finally, in order to satisfy the ultra-wideband (UWB) criteria, novel bandpass filters with their bandwidth larger than 100 % are proposed using both microstrip and CPW structures. Based on the lumped-element highpass filter prototype, the microstrip-to-CPW transition structures are used to implement series capacitors; while the short-circuited stub structures are employed to realize the shunt inductors. Being adopting the quasi-lumped elements in the filter design, the proposed UWB filters have the sizes more compact than most of published UWB filters. Another technology using a split-mode resonator is also presented for developing the UWB filters. The split-mode resonator is formed by introducing a CPW short-circuited stub into two λ/4 CPW stepped-impedance resonators. By this approach, the fabricated four-pole UWB filter has good performance and compact size as well. In addition, to suppress the unwanted radio signals around 5.8 GHz, the proposed five-pole and four-pole UWB filters with notch-band structures included are also introduced.
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