The Investigation Of Low Loss Hexagonal Ferrite In UHF Frequency Range For Antenna Miniaturization Design

As the key equipment of communication system,the performance of antenna is very important.With the development of terminal communication equipment towards miniaturization,thinness and high frequency,the degree of internal integration of the equipment is also getting higher and higher.As the design space of the antenna is constantly compressed,the research on antenna miniaturization is imperative.Hexagonal ferrite is one of the candidate materials for miniaturization of UHF antenna due to its double complex characteristics,high theoretical cut-off frequency,high quality factor and thermal stability.However,there is an order of magnitude difference between the magnetic loss and the dielectric loss,and the high magnetic loss will greatly affect the performance of the antenna.How to achieve low magnetic loss in a wide frequency range is still a big challenge.At the same time,the influence of magnetic parameters on antenna performance is also widely concerned by antenna engineers.Therefore,this paper focuses on these problems and designs a miniaturized UHF antenna based on the optimized electromagnetic parameters.First of all,this article takes hexagonal ferrite materials as the research object,and aims to prepare low loss materials which can work in ultra-high frequency bands.The effects of different sintering temperature,subsequent ball milling time and annealing temperature on the phase structure,microstructure morphology,static magnetic parameters and magnetic dielectric properties of the materials were investigated under the condition of iron deficiency formula and the premise of submicron particle size pre-firing material.The results show that when the chemical formula of the experimental formula is3Ba O·2Co O·10.4Fe₂O₃ and the pre-firing particle size is submicron,the temperature of the formation of Z phase can be reduced.In the ball milling process,the upper frequency of the flat segment of the magnetic permeability in the magnetic spectrum increases with the decrease of grain size.For the ferrite material sintered at 1200?,after pre-grinding for 6h,second-stage ball milling for 6h,and annealing at 750? to remove the internal stress,the upper limit frequency of the flat section of the imaginary part of the magnetic permeability in the magnetic spectrum increases to three times.At the frequency point of 1.9GHz,the magnetic loss tangent of the material decreases from 0.08 to 0.007,and between 1.9 and3GHz,the magnetic loss tangent of the material is between 0.007 and 0.12,the dielectric loss tangent is less than 0.02.Secondly,based on the measured electromagnetic parameters of the above hexagonal ferrite material,HFSS software is used to simulate the influence of magnetic dielectric parameters of different substrate materials on the radiation performance of dipole antenna.The center frequency of the control dipole antenna remains unchanged,and the length of the dipole arm decreases when the real part of the permeability is introduced into the substrate material;Moreover,under the premise of not affecting the antenna gain performance,the introduction of appropriate magnetic loss tangent into the substrate material is beneficial to expand the bandwidth of the dipole antenna.At the same time,HFSS software is used to design a multi-frequency communication frame slot mobile phone antenna.At 2.5GHz,the antenna is designed based on the electromagnetic parameters of the hexagonal ferrite material annealed at 750?,its center frequency point moves to low frequency,and the size can be reduced by 9.3%.The antenna miniaturization is realized.