Research And Design Of Ultra Wideband Filters With Notched Bands

Since the Federal Communications Commission approved the 3.1 GHz~10.6 GHz band as a license-free band,UWB(ultra-wide band)wireless communication technology has attracted wide attention in academic and industrial fields due to its advantages of high-speed communication,high confidentiality and low power consumption.As a key passive device in UWB wireless communication system,the performance of UWB filter directly affects the quality of the whole communication system.In practical applications,due to the conflict between UWB standard frequency band and some commercial frequency bands,the problem of signal interference gradually highlights.Therefore,UWB filter design pursues low cost,miniaturization,high performance and steep notch bands.In view of this trend,a series of research and design of notch UWB filters are carried out based on the theory of multi-mode resonators.Firstly,the theory of multi-mode resonance is studied in details,and the characteristics of the traditional step-impedance loaded resonator are analyzed.An ultra-wideband filter is designed based on the improved step-impedance loaded resonator structure,Aiming at the interference of X-band satellite signals in UWB,a single notch UWB filter is designed by proposed open-circuit branch notch structure.The 3 dB bandwidth of the filter is 2.6-11.2 GHz,the insertion loss is less than 0.9 dB,and the phase mutation occurs at 8.11 GHz.Its attenuation reaches 24.5 dB,which realizes the steep single notch bands and lays the foundation for the subsequent multi-notch design.Then,aiming at the interference of signals such as WLAN and X-satellite in UWB,a novel dual-mode folded notch structure is designed by cascading and folding the open-circuit branch notch structure.The dual-folded notch structure is coupled with the above UWB filter structure to realize the dual-notch filter.Through further fabrication and testing,the bandwidth of the filter ranges from 2.6 to 11.2 GHz,the insertion loss is less than 1.08 dB,the phase mutation occurs at 5.61 GHz and 7.81 GHz,and the notch attenuation exceeds 15 dB.Therefore,the dual-notch filter meets the need of dual-frequency suppression in UWB communication,but the rectangular coefficient of the filter is not sharp enough,and the frequency selectivity needs further improvement.Therefore,a triangular ring branch resonator is proposed based on the step impedance loaded resonator mentioned above.By analyzing the characteristics of the resonator,an ultra-wideband filter with steep rectangular coefficients is designed.At the same time,in order to enhance the coupling strength between the filter structure and the resonant unit and make full use of the structure space of UWB filter,two notch structures of the symmetrical E-type and C-type are proposed.By coupling the two notch structures with the filter structure,a three-notch filter is realized.The filter has3.01-11.26 GHz bandwidth,less than 1.19 dB insertion loss,less than-10 dB return Loss,steep slope of upper and lower cut-off bands.Phase mutation occurs at 3.71 GHz,5.31 GHz and 8.01 GHz,and notch attenuation exceeds 20 dB,which can effectively suppress interference in ultra-wideband WiMAX,WLAN and X satellite.In conclusion,this paper systematically studies and analyses the UWB multi-notch filters.The designed multi-notch filters have the advantages of low loss,high selectivity and better notch bands,and has a good application prospect in UWB communication field.