Investigation On BaM Ferrite And The Application In Quasi-planar Circulator

The microwave ferrite circulators,which are made by utilizing the gyromagnetic properties of the microwave ferrite material,are basic and indispensable devices in microwave radio frequency systems.The bias magnetic field of the traditional circulator with soft ferrite as the substrate needs to be provided by the permanent magnet,which is not conducive to the miniaturization of millimeter wave systems.M-type hexagonal ferrite materials can use their own anisotropic field to construct the required bias magnetic field for circulators,which can realize the self-bias of circulators,and have great significance for the development of planarization and lightweight of circulators.Firstly,the traditional oxide ceramics method was used to prepare BaM hexagonal ferrite suitable for Ka-band quasi-planarized circulators,and the effects of iron deficiency,preparation processes and additives on the performance of M-type barium ferrites were investigated.The results show that:?1?Moderate iron deficiency promotes grain growth,increases the material's 4?M_s and 4?M_r,and reduces the ferromagnetic resonance linewidth of the material,while excessive iron deficiency decreases the material's 4?M_s and 4?M_r,and increases the ferromagnetic resonance linewidth of the material.?2?The average grain size of the sintered body decreases first and then increases with the increase of calcination temperature,and the orientation first increases and then decreases with the increase of secondary ball milling time.For BaM ferrite materials for Ka-band quasi-planar circulators,the suitable calcination temperature and secondary ball milling time are 1100?and 18 h,respectively.?3?With the increase of SiO₂ doping constent,the average grain size first decreases and then increases,the coercive force first increases and then decreases,4?M_s and 4?M_r decrease.?4?As the sintering temperature T_H increases,the degree of densification of the sintered sample gradually increases,the average grain size,4?M_s and 4?M_r gradually increase,and the coercive force gradually decreases,?H gradually decreases.?5?With increasing the forming magnetic field from 1 T to 1.4 T,the performance of Ba_0.8La_0.2Fe_11.8-xCu_0.2O_19-?ferrite was slightly improved.Secondly,based on the self-developed M-type barium ferrite material,combined with the simulation size of a full-ferrite substrate quasi-planarized circulator under ideal magnetic parameters,a full-ferrite substrate quasi-planarized circulator model is established under actual magnetic parameters.The optimized results show that,within35.5³6.3 GHz,S₁₂ and S₁₁ are both less than-20 dB,and the S₂₁ greater than-2.7 dB,standing wave ratio?VSWR?less than 1.22,bandwidth is 0.8 GHz,size is 3.5*2.86*0.2mm³.According to simulation results,the Ka-band full-ferrite substrate quasi-planarization circulator were fabricated via lithographic process and thin-film deposition technology.The measurement results show that the center frequency of the Ka-band full-ferrite substrate quasi-planar circulator is 32.8 GHz,the insertion loss is15.8 dB,and the isolation is 39.9 dB.Finally,based on the self-developed M-type barium ferrite material,a simulation model of a Ka-band composite substrate quasi-planarized circulator is established and optimized.The results show that when the length of the small Y junction is small,the width of the small Y junction effect on the working frequency of the circulator is small.Adjusting the length of the small Y junction can adjust the working frequency of the circulator.With the decrease of the coupling angle,the return loss and isolation are increased,and the circularity is improved.When L₂=0.97 mm,W₂=0.25 mm,L₃=0.44mm,W₃=0.2 mm,y_L=0.65 mm,the circulator's impedance matches well.Compared with the simulation results of a full-ferrite substrate quasi-planar circulator,the energy loss of the composite substrate quasi-planar circulator is 16.2%lower.As the residual magnetization increases,the S₁₁ gradually increases,the S₂₁ and S₁₂ gradually decreases,and the circular effect deteriorates,the residual magnetization range of the circulator with better circular effect is 2850³750 Gs.