Preparation Of M-type Ferrite Material And Its Application In X-Band Self-biased Circulator

As a passive device with one-way signal transmission,circulators are widely used in various radar systems.Traditional circulators require external magnetic steel to provide a bias magnetic field,which is not conducive to the development of small and lightweight radar systems.M-type hexagonal ferrite has high coercivity,high remanence ratio and high anisotropy,which can provide a self-bias field for the operation of the circulator,and completely get rid of the constraints of external magnetic steel.However,for X-band applications such as long-range detection radar and urban weather warning,the high-anisotropic M-type hexagonal ferrite can no longer meet the frequency requirements of the device.It is extremely urgent to develop the preparation of M-type ferrite materials and its application in X-band self-biased circulators.First,the solid-phase sintering method was used to prepare M-type hexagonal ferrite,and the influence of the main formula and additives on the performance of M-type ferrite was explored.The research results show that:appropriate amount of Cu²⁺substitution can promote the sintering and densification of BaM ferrite.As the amount of Cu substitution increases,the M_r/M_s of the material first decreases and then increases,while H_c and H_agradually decrease.And at the same time,for an appropriate amount of iron deficiency it is beneficial to enhance the sintering activity of BaM ferrite,improve the M_r/M_s,and reduce?H.The EPMA analysis shows that the introduction of Cu O in the main formula and additives respectively can form a Cu²⁺concentration gradient in the grain and between the grain boundaries,which hinders the domain wall displacement and then increases H_c.Cu O additives can promote liquid phase sintering.With the increase of Cu O doping,M_r/M_s and H_a are basically unchanged,and H_c and?H gradually decrease.The appropriate amount of CaCO₃ additives can significantly improve the compactness and M_r/M_s of BaM ferrites,and H_c and?H of the material all gradually decrease with the increase of CaCO₃ doping amount.Secondly,based on the above-mentioned optimized main formula and additives,the influence of key preparation technologies on the performance of M-type ferrite was explored.The research results show that the appropriate pre-sintering temperature can promote the densification and uniform growth of grains,and increase the M_r/M_s and H_cof the material.As compared with the planetary ball mill,the roller ball mill and the horizontal high-energy ball mill have higher ball milling efficiency.The uniformity of the grinding powder is better.The H_c of the material gradually increases with the increase of the planetary ball milling time,first increases and then decreases with the increase of the drum-type ball milling time,and gradually decreases with the increase of the horizontal high-energy ball milling time.The suitable sintering temperature can contribute to the improvement of M_r/M_s and decrease of?H,but the H_c gradually decreases with the increase of the sintering temperature.When the pre-sintering temperature is 1000?,roller type ball milling is adopted,the ball milling time is 20 h,and the sintering temperature is 920?,the overall performance of the material is better.The H_c is 841 Oe,M_r/M_s is 0.84,4?M_s is 3.55 k Gs,H_a is 13.58 k Oe,and?H is 315 Oe.Finally,based on the self-developed M-type ferrite material,the structure of the X-band self-biased circulator was optimized and simulated.The structural parameters of the optimized X-band self-biased circulator are:h=0.26 mm,R=1.63 mm,w₁=0.96 mm,l₁=1.98 mm,w₂=0.19 mm,l₂=1.59 mm,w₃=0.46 mm,l₃=2.00 mm,w_y=0.2 mm,and l_y=2.16 mm.Meanwhile,the return loss and isolation of the X-band self-biased circulator in 8.95?9.15 GHz are both greater than 15 dB,and the insertion loss is less than 1.88 dB.