U-typed Ferrite Material Preparation And Its Application In Ku-band Circulator

In the modern communication field,common microwave devices such as ferrite circulators,phase shifters,and isolators are widely used in the microwave field.The ferrite circulator is an important part of the microwave circuit,which acts as intermediate coupling,separation of transmission and reception,impedance matching,and interference removal.The high-speed development of modern communication technology promotes the development of ferrite circulators to be low loss,high frequency,broadband,miniaturization and integration.The traditional circulator requires an external magnetic steel to provide a bias magnetic field,which greatly increases the volume and mass,and has become a key obstacle to device miniaturization and integration.The new self-biased circulator can maintain the circulatory performance with a low layout magnetic steel or without the magnetic steel,so as to realize the miniaturization and integration of the device.Based on this application requirement,this article focuses on the fabrication of U-typed hexagonal ferrite material and its application in the Ku-band self-biased circulator.Ni₂U ferrite materials with high remanence ratio（M_r/M_s≥0.9）,high coercivity（H_c>1500 Oe）,high and adjustable anisotropy field（H_a）,low ferromagnetic resonance linewidth（ΔH）are prepared by a traditional oxide ceramic technology and suitable for Ku band.The effects of ion(La³⁺,Al³⁺)doping and preparation process on the properties of U-typed barium ferrite materials are explored.The results show that:（1）With the increase of La³⁺substitution content（x）,the crystal grain growth rate dcreases,the crystal grain size also decreases,the density of the sintered samples increases,and the saturation magnetization（4πM_s）first increases and then decreases.It reaches the maximum when x=0.2,and the coercive force also shows a trend of increasing first and then decreasing.Finally,the optimal substitution amount of La³⁺is that x=0.1;（2）With the increase of the mass ratio of balls to material for the secondary ball milling,the particle size of the secondary grinding powder gradually decreases,the residual magnetization ratio in the c-axis direction increases,and the density of the sintered samples gradually decreases.The density first increases and then decreases,the porosity first decreases and then increases,the average grain size increases,the coercivity gradually decreases,and the saturation magnetization first increases and then decreases.When the ball-to-material ratio is 12:1,the magnetic ratio is high to 0.90;the magnetic anisotropy field decreases slightly,and the linewidth of ferromagnetic resonance continues to decrease;（3）With the increase of Al³⁺substitution（x）,the density decreases,the porosity increases,the average grain size decreases,the saturation magnetization gradually decreases,and the remanence ratio remains basically unchanged,The coercivity gradually increases and reaches the maximum value of 1488 Oe when x=0.8;The ferromagnetic resonance linewidth gradually decreases,and the magnetic anisotropy field is basically unchanged;（4）With the increase of pre-sintering and quenching temperature,the particle size of the secondary ball-milled powder decreases,the density increases,the porosity decreases,the grain size increases,the saturation magnetization 4πM_s gradually increases,and the coercivity gradually decreases.The suitable quenching temperature is 300℃;（5）As the sintering temperature increases,the grain size increases,the density of the sintered sample and the saturation magnetization first increase and then decrease,and the coercive force gradually decreases;the optimal sintering temperature is 1100℃.Based on the above-mentioned U-typed hexagonal ferrite material,the self-biased circulator is designed and studied.First,according to the principle of the junction circulator,the circulatory law and the impedance matching requirements of the microstrip line,a self-biased microstrip circulator with double Y junctions and full-ferrite substrate is designed.The HFSS software is used to simulate the initial model and optimize various parameters,and the final simulation results of the full-ferrite substrate Ku-band self-biased circulator are obtained.The simulation results show that the suitable size of the ferrite substrate is 7.8×7×0.25 mm³.In the frequency range of 15.4～16 GHz,|S₁₁|and|S₁₂|are both greater than 15 d B,and|S₂₁|is less than 2.5 d B and reaches the minimum of2 d B at 15.7 GHz.Secondly,combined with the simulation results of the ferrite substrate self-biased circulator,the initial simulation model of the composite ferrite substrate self-biased circulator is designed and calculated.The HFSS software is used to simulate the initial model and optimize the parameters of the circulator,and the final simulation results of the Ku-band composite ferrite substrate self-biased circulator are obtained.The simulation results show that the suitable size of the circulator substrate is 6.2×5.6×0.25mm³.At 16.6～17.3 GHz,both the return loss|S₁₁|and the isolation|S₁₂|are greater than15 d B,and both are greater than 20 d B at 16.9 GHz,the insertion loss is less than 2.5 d B and the maximum value is 1.85 d B.Compared with the full-ferrite substrate self-biased circulator,the insertion loss is reduced,and the volume of the circulator is reduced by36.4%.