Investigation On Gyromagnet And High Squareness Ferrite Applicated At Ku-band Frequency

With the development of electronic communication technology,passive phased array radar is widely used for long-range detection and identification.Ferrite phase shifter switch is a key component in passive phased array radar system.Therefore,it is of great significance to improve the performance of microwave ferrite phase shifter switch and reduce the size of the device.The performance of a ferrite phase shifter switch is closed related to the ferrite material,so the performance of the ferrite material plays an important role for the phase shifter and even the entire phased array radar.For high-power ferrite switch materials,how to develop high-performance ferrite materials is still a key topic nowadays.According to the performance requirements of high-power ferrite phase shifter switches in Ku-band phased array radar,the research in this paper was carried out basing on the lithium ferrite via a tratiditional oxide ceramic process.Effects of the formulas,additives and sintering process on Li-based ferrites were investigated in detail.The LiTiZn ferrite applied in phase shifter switches was fabricated,which possesses suitable saturation magnetization,high squareness ratio,high Curie temperature,low coercivity and low loss.Formulation system research based on Li_0.5Mn_0.08Fe_2.42O_4-δferrite was investigated.Firstly,Ti⁴⁺ion substituted Li-based ferrite was fabricated.The results show that Ti⁴⁺substitution can effectively promote the solid-state reaction in sintering process,increase the grain size,and reduce the porosity.At the same time,Ti⁴⁺ions are apt to enter the B site of ferrite,so saturation magnetization（4πM_s）reduces.In addition,K₁value of the samples decreases at the same time,which is benefit for decreasing coercive force（H_c）and ferromagnetic resonance linewidth（ΔH）.But the non-magnetic Ti⁴⁺ion reduces the Curie temperature（T_c）and squareness ratio（B_r/B_m）.Because the H_c andΔH of Ti⁴⁺ion substituted lithium ferrite samples are still high,Ti⁴⁺and Mg²⁺ion substitution was carried out then considering that both Ti⁴⁺and Mg²⁺ions are easily to enter the B site of the ferrite and may reduce the 4πM_s,H_c andΔH of the material.So a joint TiMg substitution investigation was carried out.Compared with that of the Ti-substituted Li-based ferrite samples,T_c of the sample is relatively higher,but its microstructure uniformity is poorer and H_c is higher accordingly.In order to effectively reduce the coercivity H_c of the material,Zn²⁺ion substitution was investigated based on the Ti-substituted lithium ferrite.The results show that Zn²⁺ion substitution promotes grain growth,increases saturation magnetization 4πM_s,reduces coercivity H_c and ferrimagnetic resonance linewidthΔH.Meanwhile,Curie temperature T_c,anisotropy constant K₁,and squareness ratio B_r/B_m reduce accordingly.B_r/B_m keeps at 0.91 when Zn²⁺ion substitution quantity z≤0.1.Based on the law of approaching saturation,ferromagnetic resonance linewidth of the Zn-substituted ferrite samples was separated.It can be seen that when the amount of Zn²⁺ion substitution z≤0.1,anisotropic linewidthΔH_a is dominant,andΔH_a occupies 70%in ferromagnetic resonance linewidthΔH when z=0.05.At this time,increasing the Zn²⁺ion substitution amount can effectively reduce the K₁ value,thereby ferromagnetic resonance linewidth is decreased.When the amount of Zn²⁺ion substitution z≥0.15,the pore linewidthΔH_p is dominant.But as the amount of Zn²⁺ion substitution increases,the Curie temperature drops significantly.To meet the demand of high Curie temperature,the appropriate amount of Zn²⁺ion substitution is0.05.In addition,in order to further reduce the material ferromagnetic resonance linewidth and dielectric loss,an iron deficiency formula study was conducted.The results show that iron deficiency generates ion vacancies in LiTiZn ferrite,which is beneficial to promote sintering and make the microstructure to be uniform and dense,so porosity reduces.When the iron deficiency is 4wt%and 5wt%,the dielectric loss（tanδ_ε）of the sample reaches the order of 10^-4.Finally,in order to further reduce the saturation magnetization and ferromagnetic resonance linewidth,meanwhile ensruing high Curie temperature.the Ti⁴⁺ion substitution quantiy was adjusted in trace on the basis of the formula with the iron deficiency amount of 4wt%.In terms of additive research,the amount of Bi₂O₃ additive was studied.The results show that the proper addition of Bi₂O₃ promotes the solid-state reaction in sintering process,reduces the porosity,and increases the grain size.When 0.4wt%Bi₂O₃ was adopted,the H_c andΔH of the sample reache the minimum.In terms of sintering process,the sintering temperature and holding time were studied.The results show that the sample has the lowest porosity and coercivity sintered at 1000℃.When sintered at1050℃,the grains grow so fast that the pores remain in the grains without being expelled timely resulting from the high sintering temperature.At this time,the Li volatilization phenomenon in Li ferrite gets worse,so the porosity increases accordingly.Prolonging the holding time can also promote the solid-state reaction.When the holding time is 2h,the porosity and ferromagnetic resonance linewidth are the lowest.However,the grains are too big and nonuniform if the holding time is too long（more than 3h）.Therefore,the suitable sintering condition is sintering at 1000℃for 2h.Through systematic researches,a high-performance ferrite material was fabricated.The properties of the sample are as follows:4πM_s=2620 Gs,H_c=114 A/m,B_r/B_m=0.91,T_c=480℃,ΔH=318 Oe,ΔH_k=3.28 Oe,ε′=15.71,tanδ_ε=5.6×10^-4.