Sir Dual-band Filter

In recent years,with the high development and the need of wireless communications,the dual-band portable telephones and WLAN(wireless local area network)are quite popular,and the dual-band filters become the key components in the front of these communications systems.Using the method of Stepped-Impedance-Resonator to realize dual-passband filters is researched in this dissertation,comparing to the traditional methods that combination filters, the synthesis of zeros and poles and so on,they have advantages of compact structure and convenient design,and the second resonant frequency of the designed dual-band filter can be controlled by the impedance ratio R_z and the length of the resonator.The structure and characteristic of Stepped-Impedance-Resonators are presented in this paper,with an emphasis on the half-wavelength Stepped-Impedance-Resonators,the advantages of the SIR and the principle to realize dual-band are researched too.And four dual-passband filters with controllable bandwidths are proposed for WLAN(IEEE-802.11a/b/g)using half-wavelength resonators.First,a modified hairpin structure of dual-passband filter is designed,compare to the typical hairpin filters,although the size of the proposed filter is reduced,yet can not avoid the disadvantage of this structure that can not both be matched within two pass-bands of dual-passband filters.Then three different structure dual-passband filters without needing any external impedance-matching block at the input and output using SIR are proposed in this dissertation,these filters appear very compact and satisfy the miniaturized design.Two filters are processed and measured according to their theory design models.The good agreement between electromagnetic simulation and test results shows the validity of the theory analysis and the design process.