Study On The Microstrip Multiband And Wideband Filter

With the phenomenal development in the communication industry, wireless communication has become one of the most popular technologies in this century. And many new wireless communication systems are proposed, verified, realized and adopted, (such as GSM, WIMAX, WCDMA, WLAN, UWB and so on), which have spurred a tremendous development in microwave filter. The demand on sufficient usage of frequency spectrum and compatible of different communication system has spured and improved the multiband and wideband filter design technology. The research work presented in this dissertation focuses on the multiband and wideband filter design in wireless communication. Based on the analysis of microstrip structures, such as Defected Ground Structure(DGS), parallel stubs, Stub Loaded Resonator(SLR) and so on, many multiband and wideband fitlers working at the wireless communication band are designed, in which the comparison and co-simulation method are adopted. The author's works mainly consist of:(1) Systemically Study on the bandpass and dualband filter design based on the DGS. The resonant and coupling prorperties of the DGS resonator is analyzed. Making use it as the resonant unit, bandpass and dual-band filters with source-load coupling are designed. The dual-resonant property of the nesting DGS Open Loop Ring Resonator (OLRR) is studied and a compact dualband filter is designed and achieved on this structure. Based on the resonant property of the DGS dualmode resonator, bandpass and dualband response with unsymmetrical transmission zeros are achieved.(2) The bandpass and dualband filter design method based on the parallel inductance coupling is proposed. The parallel inductance coupling effect of the parallel shorted stub is studied and utilized to design resonator-coupled bandpass filter. Because the parallel stub is with strong coupling in the high frequency, so a dualband filter with wider second pass-band is realized by combing it with SLR, in which the co-simulation si used..(3) Some novel type of dualband and triband filters are designed, which are based on the SLR and hybrid structure. The multi resonant frequency property and coupling property of the SLR is carefully studied and used to design dualband filter with high selectivity. Based on the research on the feed structure of the Defected SIR(DSIR) and OLRR, and a common coupling structure with the property of provided independent external coupling to each resonator is realized. A dualband filter and duplexier with independent passband design are achieved on this feed structure. And a triband filter is also achieved on this coupling structure. By using the SLR and DSIR as resonant unit, the tri-band filters working at the wireless communication band are designed, in which a'T'-shaped feed structure and a novel couplings structure used between SLRs are proposed(4) Study on the co-simulation of Ultra-Wideband filter (UWB) design by the method of assembling lowpass and highpass property of components. The interdigital coupling capacitance combined with the parallel shorted stub is used to form the highpass response and the high impedance microstrip stubs are used to form lowpass response. A UWB performance is achieved with the two filters in co-simulation design method. And the transmission property of an improved Lange coupling structure and the shorted SIR stub is proposed and studied. By combing the Lange coupler structure with shorted SIR stub, a UWB filter is fastly designed based on the usage of cascaded network idea and co-simulation method.