Research And Design Of Multiple-mode Microstrip Filters

Filters play important roles in RF/microwave systems. With the rapid development of modernwireless communication, filters with high performance, small size and low cost are desired. Thisthesis mainly concerns on analysis and design of microwave filters based on multiple-mode principle.Meanwhile, odd-even mode method, based on transmission line theory, is appiled to analyze theresonant frequencies of multiple-mode resonator. Some novel multiple-mode resonators and couplingstructures are presented and different multiband filters with good characteristics are designed usingthese resonators.The main work in this thesis can be summarized as follows:1. A stub loaded resonator is introduced. Based on the odd-and even-mode equivalent circuits,the resonance characteristics of the resonators are investigated. By introducing source/load coupling,dual-mode bandpass filter is realized. The open stub at the central plane is used to control the evenmode resonant frequencies, whereas the odd mode ones are fixed. The filter has good selectivity andgood stopband responses.2. A novel quadruple-mode resonator is proposed based on the dual-mode resonator. Three openstubs attached to high impedance microstrip line are mainly applied to adjust the four resonantfrequencies. A broadband bandpass filter with sharp skirt and wide upper-stopband performance isproposed using the quadruple-mode resonator.3. A compact and high selectivity dual-band dual-mode microstrip bandpass filter (BPF) isproposed using the single short-circuited stub loaded stepped-impedance resonator. The resonatorutilizes the odd/even mode resonators’ fundamental resonant frequencies and second harmonic onesto generate the first and second passbands, respectively. Five transmission zeros are created toimprove the selectivity.4. A dual-band filter with independently designed bandwidth is proposed. Either of thedual-mode resonators can not only separately generate one passband but also control the passbandperformance. The filter located at GPS application and WLAN application is fabricated which canachieve compact size and good frequency selectivity.