Preparation And Properties Of High Q Microwave Dielectric Ceramics For Microstrip Filter

In recent years,with the rapid deployment of the fifth generation of mobile communication technology（5G）,the massive data transmission brought by new application scenarios such as virtual reality,autonomous driving and telemedicine will inevitably lead to a multiplication of power consumption.Taking 5G base station as an example,the introduction of Massive MIMO technology makes the energy consumption of 5G base station reach three times that of the 4G base station.How to reduce the power consumption of the microwave system becomes the primary problem of 5G development.High-quality factor（Q-value）microwave dielectric ceramics are the basis of low-power microwave devices.The comprehensive improvement of the dielectric properties of microwave dielectric ceramics is the key to solving 5G power consumption problems.Based on MgTiO₃,high-performance microwave dielectric ceramic materials with suitable dielectric constant and high Q value were prepared by doping and compounding.Based on the MgTiO₃ ceramic substrate,a C-band（4～8GHz）low-loss ceramic-based microstrip line filter applied to 5G networks was developed,which has important theoretical and application value.The main research contents and results are as follows:Firstly,to improve the quality factor of MgTiO₃ ceramics,MgF₂ was used as a dopant,the liquid phase was produced by low-melting fluoride to promote the densification process of ceramics,and the crystal phase composition of ceramics was improved by excessive Mg doping.On this basis,the following analysis was carried out:（1）the mechanism of the influence of the R-P phase structure on the quality factor was explored;（2）based on the characterization of bulk density and the trend of leakage current,the relationship between microstructure and dielectric properties of microwave dielectric ceramics was established.Finally,the MgTiO₃-3wt%MgF₂ ceramics with the following microwave dielectric properties:ε_r=18.09,Qf=262,900GHz（@8.98GHz）,τ_f=-41.5×10^-6/℃were developed,which is expected to meet the needs of low-loss applications demand of 5G microwave communication,but the temperature coefficient of resonance frequency needs further improvement.Furthermore,to adjust the temperature coefficient of the negative resonance frequency of MgTiO₃ ceramics to near zero,the(Ca_0.8Sr_0.2)Ti O₃ system with a positive resonance frequency temperature coefficient was used for recombination.Based on the phase composition and microstructure analysis of the composite system,the intrinsic correlation between microwave dielectric properties and phase composition of the composite ceramics was established.Finally,3wt%MgF₂ doped 0.95MgTiO₃-0.05(Ca_0.8Sr_0.2)Ti O₃ ceramics with the following microwave dielectric properties:ε_r=19.99,Qf=90,100GHz（@8.72GHz）,τ_f=-2.9×10^-6/℃were developed,meeting the application requirements of low-loss microstrip filter substrate.Finally,a 4th-order C-band parallel-coupled microstrip line filter with a center frequency of 6.1 GHz was developed based on MgTiO₃-3wt%MgF₂ ceramic substrate.Based on the Agilent ADS software system,the influence of various performance parameters of the substrate on the S parameter of the filter was analyzed.The final test results are as follows:filter center frequency f₀=6.1GHz,relative bandwidth FBW is about 6.5%,in-band insertion loss|S₂₁|is less than 3d B,optimal value is 1.18d B,in-band return loss|S₁₁|is greater than 15d B,at 5.4GHz the|S₂₁|value is greater than 30d B,and it is greater than 20d B at 6.8GHz,which provides a new device option for the 5G network C-band microwave system implementation,and has important application value.