Study On Synthesis And Design Of Microwave Multiband Filter

Recently, the rapid development in wireless communication has created a largedemand of filters with multi-band response in the modern wireless communication, suchas the wireless code-division multiple-access(WCDMA), wireless local areanetworks(WLANs) and so on. In multi-band communication systems, multi-band filterscan reduce the volume and mass of the circuit, make the system simple and decrease themanufacture cost. Therefore, it is significant to investigate the theory on designingmulti-band microwave filters.Based on the analysis of synthesis method and structure for multi-band microwavefilters, such as, defected ground structure split ring resonator(DGS SRR), foldeddefected structure split ring resonator(FDS SRR)， resonators with stub loaded and soon. Some multi-band filters working at the wireless communication band are designed.The main contributions of this paper are how to achieve the miniaturization and highout-of-band suppression of multi-band filters. The author’s work mainly consists of:1. Systematically study on the frequency transformation for dual-band filters, basedon which the frequency transformation for triple-band filter is presented. Both of theequivalent circuits are constructed。The coupling coefficients and external qualityfactors for analytical equations are derived. Based on the proposed synthesis theory,several examples of theoretical filter equivalent circuits and examples of theoreticalfrequency responses are also presented.2. Systematically study on the resonators with open stub, short stub, SIR stubloaded, respectively. Several novel types of dual-band and triple-band filters aredesigned based on the stub loaded resonator. The multi-resonance frequencies of theresonator with stub loaded are carefully studied and used to design multi-band filterswith high selectivity. The high out-of-band suppression filtering responses of themulti-band filters using stub-loaded resonators are achieved by introducing transmissionzeros with0-degree feed structure and dual parallel coupling feedline.3. Based on frequency transformation method, the theoretical design of multi-bandfilter is then realized by a group of multi-band resonators as the building block of thefilter. High out-of-band suppression filtering responses are achieved by cross-couplingand resonators with the different lengths open stubs loaded. A novel dual-moderesonator is used to replace the building block consisting of two common resonators.Due to the decrease in number of resonators, the size can be reduced by half. Thefrequency transformation method can reduce the complexity of simulation and avoid the blindness of design, when the dual-mode resonator is used to realize dual-band filter.4. Systematically study on the split ring resonator(SRR), which includingmicrostrip split ring resonator and defected ground structure split ring resonator(DGSSRR). Controllable-length split ring resonator(CLSRR) and folded defected groundstructure split ring resonator(FDGS SRR) are presented. The analysis on the resonantand coupling properties of the two resonators has been done. The coupling intensitybetween resonators with different position is analyzed. The coupling properties betweenresonators are firstly studied with the detail of position. Based on the analysis, themulti-band filters are designed by CLSRR and FDGS SRR.5. Respecting FDGS SRR, folded defected structure split ring resonator(FDSSRR) etched on the top surface of microstrip is presented. Based on the analysis of FDSSRR, the analytical equivalent-circuit models are proposed for the isolated and coupledFDS SRR. A substrate integrated waveguide(SIW) with FDS SRRs etched on thewaveguide surface is investigated. The application of this waveguide and FDS SRRcombination technique to the design of miniaturized SIW bandpass filters is improvedby half-mode theory. The method of filter design is verified. These proposed filtersexhibit high selectivity and compact size due to the employment of the FDS SRR.