Design Of Planar Dual-band And Wide-band Bandpass Filters Based On Multi-mode Resonators

Portable and miniaturized is one of the trends of wireless communication systems development.Because of the nonrenewable of spectrum resources and situation of coexistence of multiple communication modes,single band communication systems with narrow bandwidth is harder and harder to meet the requirement of modern communication.Due to the advances of simple structure,easy to be fabricated and low cost,and features of convenient,high efficiency and flexible in compact multiband and wide-band filter design,multi-mode filter has been become a hot issue in modern communication systems research.In this paper,stubs loaded resonator is being in-depth researched firstly,then a four modes short stubs loaded resonator using nested structure is proposed,miniaturized of the resonator is realized by the nested structure and fold the microstrip,and co-planar wave guide feeding structure is employed to design practical external ports,and a compact dual-band bandpass filter with independent control of frequencies and bandwidth is achieved according to the distribution of the odd-and even-mode frequencies.In the section of wide-band filter design,two compact wide band bandpass filer with features of free control of resonant frequencies and bandwidth based on a same resonator is presented.In order to enhance the coupling strength of ports,one of the filter is introduce defected ground structure to enhance port coupling and realize wide bandwidth,and the other one is apply co-planar wave guide ports to obtain tight coupling,moreover,one coupling path is added to control the transmission zero and achieve better selectivity.Finally,a novel structure tri-mode defected ground structure resonator is proposed,and the resonant characteristic is analyzed to find means to control the resonant frequencies.This resonator is applied to design wide-band bandpass filter in the end.