The Research Of Microwave Planar Multi-band Filter

The emerging wireless communication technology makes original limited spectrum more crowded.The multi-band device has been proposed and always attracted many scholar's attention.Meanwhile,microwave circuits in modern communication systems are more complex,and the intensity of device and modules is constantly increasing.Therefore,traditional device structure and modules are facing the challenge of transformation and upgrade.As one of key device in multi-band transceiver,multi-band filter directly affects the quality of whole communication system because of its frequency selectivity.Microwave planar multi-band filter can simultaneously extract desired signals and suppress the spurious interference.In addition,it can be integrated with planar circuit and greatly reduce the size and cost of communication system.By adjusting the impedance ratio and the electric length,stepped impedance resonator(SIR)can control the resonant frequency,what's more,it can be integrated with 1/4 wavelength resonator(QWR),defected ground structure(DGS),shorted circuited stub loaded resonator(SSLR)and open circuited stub loaded resonator(OSLR)to provide a broad stage for filter synthesis and design.In this thesis,the application of SIR in multi band filter is investigated because of its highlight resonance characteristic.At first,the input admittance and resonance characteristic of dual-section SIR are deduced and analyzed in the thesis,the input admittance is expressed by polynomial multiplication;and the input admittance and resonance characteristic of tri-section SIR and tri-section loaded with open stub is researched as well as general chebyshev filtering function and theory about quasi-bandpass section.Meanwhile,the application research in microwave planar multi-band filter is investigated.Then dual-band bandpass filter is designed to achieve high out of band isolation according to tri-section loaded with open stub.Further research is investigated that wide stopband with dual-band bandpass filter can be achieved by adjusting the impendence ration and improving the feed network when DGS is etched on ground plane.Then,tri-band bandpass filter is designed based on general chebyshev filtering function in this thesis.Half wavelength SIR and QWR are employed to form dual transversal cross-coupled path.As a result,eight transmission zeros(TZs)can be realized with excellent selectivity and high out of band rejection.Meanwhile,DGS is introduced as an efficient way to micro-adjust the coupling coefficients without changing top layout of proposed filter.Finally,the theory of quasibandpass section is investigated to design dual-band quasi-bandpass filter,which is consisted of NRN(non-resonating nodes)and reconfigurable resonator.The reconfigurable resonator is loaded in NRN,then the cascaded quasi-bandpass section is coupled instead of traditional coupling between resonator to improve tuned range of frequency.As a result,center frequency and band of dual-band reconfigurable filter can be controlled by change the capacitor values,and out of band rejection is above 60 dB,even 78 dB in some special cases.EM Simulator is employed to design filter in the thesis,then filter is fabricated by standard PCB technology and measured by HP8510 B network analyzer.The rationality and feasibility of method proposed in the thesis is proved by good agreement between measured and simulated results.