Design Of Circulator With Filtering Characteristics

As important components of RF front-end system,circulator and filter play an irreplaceable role in wireless communication system.Firstly,thesis studies the material parameters of ferrite,external magnetic field bias,ring conditions,various structural forms of ferrite ring and impedance matching methods,and then studies the frequency characteristics of lumped parameter filter,step impedance resonator filter,microstrip hairpin resonator and the generation mechanism of out of band suppression points,which provides a theoretical basis for the design of filter ring.The research contents of this subject mainly include:The integrated design of X-band filter circulator is completed.By analyzing the working magnetic field of the traditional ferrite circulator,the hairpin resonator is selected as the basic filter structure,and the second-order hairpin filter is specially bent to replace the traditional central junction.The central junction is connected with the external port by electromagnetic hybrid coupling,and the input-output matching is completed by twoorder quarter wavelength impedance converter.The filter circulator is between 7.95-8.43 GHz,the in passband isolation is greater than 20 d B,and the out of band suppression is greater than 16 d B at 7.5GHz and 9GHz.The design of cascaded X-band nonreciprocal filter based on circulator is completed.Firstly,a ferrite circulator working in X-band is designed based on microstrip line structure.The whole circulator adopts a single Y-junction structure,and a quarter wavelength impedance converter is used between the central junction and each standard microstrip port to complete impedance matching.At the same time,a bandpass filter working in the frequency band of 8.3-8.8GHz is designed by using the suspended bandline structure.The filter adopts the design of 4-order quarter wavelength step impedance resonator,adds notch structure at the input and output port to strengthen its out of band suppression,and uses stepped impedance line to complete input-output matching.Finally,the circulator and filter are simulated in cascade.The final simulation results show that the circuit structure has good frequency characteristics in the frequency band of 8.3-8.8GHz.The stripline circulator and reconfigurable lumped parameter filter are cascaded to complete the design of reconfigurable nonreciprocal filter based on circulator.Firstly,based on the stripline structure,an UWB double Y-junction circulator operating at 0.8-2.3GHz is designed.The transition structure from stripline to microstrip line and the miniaturization design of double Y-junction central junction are designed to realize the ultra wideband matching of ferrite circulator.Then,the reconfigurable nonreciprocal filter is designed by cascading.The final simulation results show that the reconstruction of arbitrary center frequency and bandwidth is realized in the range of 0.8-2.2GHz.