Fabrication And Application Technologies Of BaM-type Ferrite

In order to promote the development of microwave systems towards miniaturization,planarization,lightweight and integration,microstrip lines are often demonstrated as the structural form of ferrite junction circulators.However,traditional microwave ferrite circulators require additional permanent magnets to provide bias magnetic fields,which is not conducive to small and lightweight devices.The M-type hexagonal ferrite has a strong magnetocrystalline anisotropy field,which can provide a biased internal field and make the circulator work well without external magnets.It is benefit to meet the development needs of the device.Therefore,M-type hexagonal ferrites and self-biased circulators are studied and presented as follows.Firstly,Ba M ferrite materials suitable for K～Ka band self-biased circulators were prepared by a traditional oxide ceramic method.The effects of ion substitution,preparation process and shape effect on the properties of M-type barium ferrite were investigated.The results show that:（1）A slight amount of Sr²⁺substitution has little effect on the saturation magnetization（4πM_s）,which can increase the coercivity（H_c）and magnetocrystalline anisotropy field（H_a）of the material,but excessive Sr²⁺substitution will lead to the decrease of 4πM_s and 4πM_r and the increase of ferromagnetic resonance linewidth;（2）Increasing the sintering temperature can increase the grain size,bulk density and 4πM_s,but decrease the H_c.（3）The 4πM_r and remanence ratio of the ferrite substrate strongly depend on the shape effect.When the normal direction demagnetization factor N_z reaches 0.58,increasing the aspect ratio can significantly increase the remanence and remanence ratio of the substrate.When the substitution amount of Sr²⁺is 0.4 and the sintering temperature is 1045°C,the comprehensive performance of the ferrite material is better.When the aspect ratio of the ferrite substrate is 34.9%,the M_r/M_m in the normal direction is 0.74 and the 4πM_r is 2982 Gs.Secondly,on the basis of the self-developed M-type barium ferrite material,combined with the working principle of the junction circulator,the structure size of the self-biased circulator is designed and calculated.The initial model of the K～Ka band all ferrite and composite ferrite substrate self-biased circulator is established and simulated by HFSS software.Based on the initial simulation results,the size parameters of the circulator are optimized.The optimization results of the self-biased circulator with all-ferrite substrate are as follows:in the frequency range of 26.5～27.8 GHz,the insertion loss|S₂₁|is less than 1 d B,the isolation|S₁₂|and the return loss|S₁₁|are more than 20 d B,and the bandwidth is 1.3 GHz.The optimized simulation results of the self-biased circulator with composite ferrite substrate are as follows:in the frequency range of24.5～28 GHz,the insertion loss|S₂₁|is less than 1 d B,the isolation|S₁₂|and the return loss|S₁₁|are both greater than 15 d B;with the decrease of 4πM_r and the increase ofΔH,the performance of the circulator deteriorates.In order to make the circulator have better performance,the 4πM_r>2400 Gs andΔH<600 Oe of the material should be guaranteed.The ferrite substrate should have a suitable magnetic anisotropy field H_a.When the anisotropic field 15 k Oe<H_a<18 k Oe,the self-biased circulator has better performance.Finally,the ferrite microstrip circulator was prepared by semiconductor process,and the performance of the circulator was tested and analyzed.The tested measurement is as follows:In the frequency range of 23～25 GHz,the circulator has a circular effect,the insertion loss|S₂₁|is less than 3.7 d B,the bandwidth is about 2 GHz when the isolation|S₁₂|is more than 10.3 d B,and the standing wave ratio is less than 1.42,and the insertion loss has the minimum of 2.1 d B at 23.6 GHz.