Low Permittivity And Low Loss Microwave Dieletric Materials And Their Research On Antenna Application

With the rapid development of 5G communication system,antenna as the eyes of wireless communication system,its miniaturization,integration,high frequency,low loss,low cost requirements are increasingly urgent,and the dielectric antenna based on low temperature co-fired ceramic（LTCC）technology is the only way to solve the above urgent needs.However,low temperature co-sintered microwave dielectric materials with ultra-low loss,LTCC microstrip patch antenna theory and design model,and antenna temperature stability are the technical bottlenecks that are still to be solved in this field at home and abroad.This dissertation mainly aims at the medium frequency band of 5G（3.3 GHz-3.6GHz and 4.8 GHz-5.0 GHz）dielectric antenna technology requirements,and resesches the formulation and process of antenna basic dielectric materials,aiming to develop low dielectric constant,ultra-low loss and meet the requirements of low temperature co-firing technology antenna dielectric microwave ceramic materials,and expand its application frequency.At the same time,according to the development of ultra-low loss LTCC material,the performance of dielectric antenna,solve the temperature stability problem of antenna,and realize the dual-band application requirements of dielectric antenna in 5G intermediate frequency spectrumIn this dissertation,silicate system ceramics Zn₂Si O₄ and CaMgSi₂O₆ with low dielectric constant and low loss were chosen as research objects.First,based on the good dielectric properties of Zn₂Si O₄dielectric ceramics,a Zn-deficient formula was used to obtain pure-phase Zn₂Si O₄ dielectric ceramics with excellent dielectric properties sintered at 1300°C:ε_r=6.451,Q×f=102807 GHz,τ_f=-32.05 ppm/°C.P-V-L complex chemical bond theory was used to guide doping,and A/B ion regulation was carried out,and mechanism of the microwave dielectric properties of Zn_1.8Si O_3.8 ceramics was studied.Zn_1.8Si_0.92Ge_0.08O_3.8 ceramics can be densified when sintered at 1275°C,by replacing Si⁴⁺with Ge⁴⁺to control the structure and dielectric properties of the materials,and the average grain size could reach 9.44μm.At this time,the dielectric properties wereε_r=6.659,Q×f=73110 GHz,τ_f=-34.12 ppm/°C.The sintering temperature of Cu_xZn_1.8-xSi O_3.8 ceramics could be significantly reduced by adding Cu O and replacing Zn²⁺with Cu²⁺,so that densification and sintering could be realized at 1010°C,which met the sintering temperature requirement of low temperature co-firing ceramic technology（sintering temperature was lower than the co-firing temperature of Cu electrode 1083.4°C）.The dielectric properties of Cu_0.1Zn_1.7Si O_3.8 were as follows:ε_r=6.700,Q×f=54128GHz,τ_f=-25.22 ppm/°C.Secondly,the ion substitution modification and low temperature sintering of CaMgSi₂O₆ dielectric ceramics were studied.The effect of(Cu_1/2Zn_1/2)²⁺composite ion content on CaMg_1-x(Cu_1/2Zn_1/2)_xSi₂O₆ ceramics was studied.During the change of x from0 to 0.025,the second phase Ca₂MgSi₂O₇ in the ceramic gradually decreased,and the pure phase CaMgSi₂O₆ dielectric ceramic was obtained at x=0.02.In terms of grain size,an appropriate amount of(Cu_1/2Zn_1/2)²⁺ions promoted the growth of grains.When the sintering temperature was 1200°C,the grain growth of CaMg_0.98(Cu_1/2Zn_1/2)_0.02Si₂O₆ceramics was uniform,and the average grain size was 1.96μm.The substitution of(Cu_1/2Zn_1/2)²⁺ions also changed the atomic packing ratio of the ceramics,and the maximum Q×f value was 45107 GHz at the maximum atomic packing ratio.The distortion trend of[MgO₆]octahedron after ion substitution was consistent with that of the temperature stability coefficient,ε_r=7.997,τ_f=-42.52 ppm/°C.Aiming at low temperature sintering,CaMg_0.9-xLi_0.2Mn_xSi₂O₆ dielectric ceramics were prepared by using Li⁺doping and adjusting the amount of Mn²⁺substitution.With the change of x from 0 to 0.15,the temperature stability coefficient first moved to the positive direction and then to the negative direction.Under the co-adjustment of Li⁺and Mn²⁺,CaMg_0.84Li_0.2Mn_0.06Si₂O₆ dielectric ceramics could be sintered at low temperature without the addition of glass phase.The densification sintering temperature was 925°C,and the relative density reached 95.47%.The Raman vibration peak of 666cm^-1 had the smallest width at half maximum（FWHM）,the largest atomic occupancy,and the smallest internal loss of the material.At this time,the dielectric properties of the dielectric ceramic are:ε_r=7.799,Q×f=36207 GHz,τ_f=-35.58 ppm/°C.At the same time,the dielectric properties of CaMg_0.9-xLi_0.2Mn_xSi₂O₆ dielectric ceramics were tested in the terahertz frequency band（0.4-1.2 THz）.The dielectric constant of ceramics was in the range of5.4-6.32,and the dielectric loss was in the range of 0.05-0.125.Thirdly,in order to adjust the temperature stability of the LTCC dielectric antenna,the method of multiphase composite dielectric ceramic was used for neutralization to prepare dielectric antenna materials with suitable dielectric constant,low dielectric loss,and met the technical requirements of LTCC.Firstly,MgO dielectric ceramics with ultra-low loss as one of the composite phases were studied.The low temperature sintering of MgO-xwt%Li F microwave dielectric ceramics was achieved by adding sintering aid Li F.As x changes from 2 to 10,the ceramic grains grew gradually,but when x>6,the grains began to grow abnormally.When 4wt%Li F was added,the grain arrangement was uniform and compact.According to the P-V-L chemical bond theory,the lattice energy was maximum and the intrinsic loss was minimum at this time.When sintered at 950°C,the dielectric properties of MgO-4wt%Li F dielectric ceramics wereε_r=9.664,Q×f=120288 GHz,τ_f=-20.66 ppm/°C.In the terahertz band test,its loss factor was between 0.0056 and 0.00866,which brought the possibility for the application of the next generation of more high frequency communication dielectric materials.Secondly,ultra-low loss MgO-4wt%Li F,CaMg_0.84Li_0.2Mn_0.06Si₂O₆ prepared in Chapter 3 and Ca Ti O₃with a maximum positive temperature stability coefficient were used to prepared three-phase composite ceramics[80wt%MgO（-4wt%Li F）-20wt%CaMg_0.84Li_0.2Mn_0.06Si₂O₆]+xwt%Ca Ti O₃.Only three-phase components were detected in XRD,and multi-phase grains could be seen in SEM.The grain morphology was closely arranged when 2 wt%-5 wt%Ca Ti O₃was added.The theoretical dielectric properties calculated by the multi-phase mixing rule were consistent with the measured dielectric properties,and excellent dielectric properties were obtained at 950°C sintering:ε_r=9.923,Q×f=45230 GHz,τ_f=-2.50 ppm/°C.Finally,based on the dielectric properties of[80wt%MgO（-4wt%Li F）-20wt%CaMg_0.84Li_0.2Mn_0.06Si₂O₆]+4wt%Ca Ti O₃ dielectric ceramics,a U-slot microstrip patch antenna applied to 5G medium frequency spectrum band was designed and simulated by CST software.Its operation bandwidth was:3.3 GHz-3.45 GHz and 4.86 GHz-4.93 GHz.At the operating frequency of 3.4 GHz,the return loss S₁₁=-14.72 d B,the V_SWR=1.45,the gain=9.12 d Bi,and the radiant efficiencyη=98.37%.At the operating frequency of4.9 GHz,the return loss S₁₁=-24.84 d B,the V_SWR=1.12,the gain=7.712 d Bi,and the radiant efficiencyη=90.66%.The application of the material under the requirements of5G dielectric antenna was verified.