Research On Novel Planar Bandpass Filter And Mixed Q Value Technique

In recent years, wireless communication systems have not gone through a revolutionary breakthrough. The development direction of more and more microwave components is improving the performance, reducing the size, utilizing the spectrum more efficiently to achieve higher date rates and lower S/N ratio. As the most important frequency selection component which decides the operating frequency of a system, the importance of the bandpass filter is obvious. Different systems have different demands of size, operating frequency and performance, which result in flexible designing of the filter. This dissertation mainly focuses on the recent engineering requirements of bandpass filters(BPF), doing research on the wideband and UWB technology, multi-band technology based on planar substrate and Mix-Q value technology on cavity filters. The main contents of this dissertation are shown as follows:Firstly, a deep research on the synthesis method of traditional tubular filter is given, and the suspended stripline(SSL) is used to achieve wideband and ultra-wideband filter response. This part shows an intensive study on the synthesis method of traditional tubular filter and the electromagnetic performance of the SSL, indicating the imponderable advantages of SSL in microwave components design. Then, the traditional synthesis method is improved to obtain the initial approximate values of the lumped elements in an ultra-wideband circuit schematic. The high-low impedance line is used to realize the ultra-wideband circuit schematic equivalently, and Q3 d software is employed in calculating the plate capacitor between two low impedance lines, which offers more efficient and accurate filter design procedure. Besides, the nonresonating node is employed with the improved tubular filter equvilent circuit firstly, which results in two independently controllable transmission zeros appeared at high and low-end stopband. At last, a novel technology called ―different height of cavity(DHC)‖ is proposed to reduce the dimension of a SSL BPF while it has lower operating frequency. Good agreement between the simulated and measured results of the three filters is observed, which proves the validity of the techniques.Secondly, the novel microstrip multi-band BPF is studied. The purpose of the multi-band BPF is introduced with the common design method in this part firstly. The frequency response characteristics of both step-impedance resonator(SIR) and stub-loaded resonator(SLR) are studied, and the symmetrical SIR and short-stub loaded resonator are both used to realize a dual-band response respecitively with the independently controllable passband. Then, a novel tri-band BPF based on two open-stub loaded SIR is proposed. This filter has symmetrical topology and meets both good performance and high demand of miniaturization. Besides, how to realize multi-band response with only one SLR is studied. At last, by introducing coupling between two loaded open-stubs, tri-band response is realized using only one SLR. The measured result of the tri-band BPF exhibits a reasonable agreement with simulated result, and this filter achieves three inpendently controable passbands with compact size, the circuit occupies only 0.106λg?0.064λg, where λg is the guided wavelength at lower passband center frequency.Thirdly, the application and simulated tuning skill of mix-Q technique are studied in depth with the coupling structure between different resonators which possess unequal Q-value. This part mainly introduces the application and significance of the mix-Q value technique, and shows the key points when designing a mix-Q value filter. Then, how to find out the most cricital cavity which affects the passband edge performance most is studied, suggestions about how to design a mix-Q value filter are summarised. Besides, the Y-matrix tuning method and Co-simulation technique are introduced with different resonators in filters designs. At last, based on electric field orientation of a dielectric resonator(DR) operating in TE01?-mode, a novel coupling method which could easily change the coupling nature between DR and combline resonator(CR) or between two DRs is presented. The positions of the transmission zeros in the filter’s response would be changed along with the coupling nature between two resonators. Two CT and CQ-based bandpass filters are simulated, frabricated and measured. Measured results confirmed the predicted performance, showing the availability of the proposed method.Finally, a summary of the whole dissertation is given with the prospects of future work.