Research And Design Of Ultra-wideband Bandpass Filter Based On Mutiple Mode Resonator

Filter is a very significant frequency selection device in communication system,which can promote the effectiveness of signal transmission.Different communication systems require specific types of filters,for example,the mobile phone communication system needs narrow-band filters to obtain high-precision frequency.While no matter what kind of communication system,filter would influence rate of the information transmission.Ultra-wideband filter emerges to promote the signal transmission effectively.In this paper,a variety of novel ultra-wideband filter structures are designed by multiple-mode resonators combined with other methods such as defected ground structures and cascading methods.The main contents of this paper can be summarized as follows:1.The background and significance of ultra-wideband filter is described,and summarize main methods of designing ultra-wideband filters,including multiple mode resonator,coplanar waveguide and cascading.2.The relevant theory of filter is described,including the main performance parameters of UWB filters,the conversion process of lowpass prototype to several different filters,and the theoretical basis of even-odd mode analysis.3.Two three-mode UWB filters are designed,which are based on third-order dual-mode resonator.The first filter employs the third-order stepped impedance resonator structures,which apply short-circuit structure and open-circuit structure in terminals respectively.The filter's main shortage is its bandwidth.The second filter's design bases on the first one,namely,loading the open-circuit stub and short-circuit stub on the horizontal stepped impedance lines respectively,and the rectangular defected ground structure enhances the coupling of filter.Both of the two UWB filters have characteristics of quasi-elliptic function,which gains steep passband edge.4.Two miniaturized UWB filters based on the ring resonators are designed,the resonator used in the first filter is the deformed structure of the ?/2 stepped impedance resonator.The single mode characteristic of resonator changes into three-mode characteristic by introducing short-circuit perturbation.The second filter increases resonant modes in passband by introducing open-circuit perturbation and short-circuit perturbation in the ring resonator symmetrically.Two filters meet the requirements of bandwidth basically,and both of them have a good rejection performance in stop-band.5.Three high performance UWB filters are designed by cascading band-pass and low-pass filters.The band-pass filter is designed based on short-circuit transmission lines,which are loading on I / O feed lines,and the low-pass filter is designed by zero-feed of I / O feed lines with different resonator structures.Single band-notched characteristics and dual band-notched characteristics of UWB filters are designed for the second and third ones by loading the open-circuit stub on I / O feed lines and short-circuit perturbation structure on resonator respectively,which have a great practical value.Three UWB filters have certain bandwidth advantages,and achieve full coverage of ultra-wideband frequency band.