Research And Degin Of Microstrip Multi-mode Ultra-wideband Filters With Notch Band

Ultra-wideband(UWB)filter is one of the important components of UWB communication system and it will affect the overall performance of the communication system.Microwave communication systems require that the filter should not only have high frequency selectivity,but also realize miniaturization.Meanwhile,some of the narrowband signals still exist in the UWB frequency range of 3.1 to 10.6 GHz.Therefore,it is also important to remove the narrowband signals and solve the problem of signal interference.The multi-mode resonator(MMR)technology could generate multiple resonant frequencies by only one resonator,which becomes an effective method to design UWB filter.In this thesis,a series of research and design of the UWB filter are carried out based on MMR theories.Firstly,a T-shaped loaded MMR is proposed in this thesis.An UWB filter is designed based on the T-shaped loaded MMR.The filter has a compact structure with high selectivity.The 3dB passband of the filter range from 3.0 to 10.8 GHz,and the insertion loss is less than 0.5 dB.Two kinds of notch structures are proposed in order to suppress the interference of narrowband signals in UWB passband.The first one is U-shaped embedded open stub.This structure has the advantages of simplicity and flexibility.A notch band centered at 8.0 GHz is achieved by etching the U-shaped embedded open stub on the UWB filter.The notch band suppresses the interference of the satellite communication signal in UWB passband.The second notch structure is square open-loop resonator.Only one resonator is used to generate dual resonant frequencies.Dual notch bands centered at 5.8 GHz and 8.0 GHz are achieved by coupling the square open-loop resonant to the UWB filter.The dual notches suppress the wireless local area network(WLAN)signal and satellite communication signal in the UWB passband respectively.Then,a structure of folded-loop resonator is proposed in this thesis.According to the analysis of the resonant characteristics,a wide band-stop UWB filter is designed based on the folded-loop resonator.The filter has a compact structure with good band-stop characteristics.The passband of the filter range from 3.0 to 10.8 GHz and the insertion loss is less than 0.6 dB.The stopband of the filter is less than-15.5 dB attenuation up to23.0 GHz.The improved band-stop characteristic overcomes the shortcomings of poorout-of-band performance of multi-mode resonant technology.In order to achieve better notch band characteristic,two types of notch structures are used.One is “W” shaped short stub loaded resonator(SSLR)and the other is complementary split rings resonator(CSRR).Dual notch bands centered at 5.8 GHz and 8.0 GHz are achieved by coupling two notch structures to the filter.Dual notch bands are independent and adjustable,and both of the lowest point are less than-26.0 dB.Finally,the designed filters are all fabricated and tested.Measured results are in sound agreement with simulation results,verified the effectiveness of the theory and design.The results show that the designed UWB filter has the advantages of compact structure,high selectivity,and good performance of notch bands.The filters meet the UWB design requirements and have a certain practical value and application prospects.