Lattice Modification And Antenna Design Of Yttrium Aluminum Garnet Ceramics

Microwave dielectric ceramics,as an indispensable base material in microwave devices,are widely used in filters,couplers,amplifiers,antennas and other devices.The excellent dielectric properties,good mechanical properties and high temperature stability of microwave dielectric ceramics ensure the stable performance and long lifespan of microwave devices in high-frequency and high-temperature environments.These properties provide a robust foundation for the stable operation of communication system.In this thesis,Y₃Al₅O₁₂ garnet ceramics were synthesized via solid-state reaction method.The specific results are as follows:（1）A series of Y_2.9M_0.1Al_4.9Si_0.1O₁₂(M=Ca²⁺、Sr²⁺、Ba²⁺、Mg²⁺、Co²⁺、Zn2+、Mn²⁺)ceramics were synthesized by solid-state reaction method,and all the samples were identified as the garnet phase.Anomalous increases in the dielectric constant occurred when elements with small ionic radii,such as Mg²⁺,Co²⁺,Zn²⁺and Mn²⁺,occupied the A site of garnet,which can be attributed to the rattling effect.The dielectric properties of samples were analyzed using Raman spectroscopy and complex chemical bond theory.When M=Mg²⁺,the microwave dielectric properties were:ε_r=9.74,Q×f=51,382 GHz,τ_f=-30.12 ppm/℃.（2）Y_3-xMn_xAl_5-xSi_xO₁₂（x=0.1-0.5）ceramics were synthesized by traditional solid-state reaction method,and the solid solution was formed in the ceramic samples without any secondary phase.When x=0.1-0.2,Y_3-xMn_xAl_5-xSi_xO₁₂（x=0.1-0.5）ceramics exhibited good compactness.However,at higher doping concentrations,the grain growth was found to be abnormally and the grain boundaries began to melt.In addition,the dielectric properties of Y_3-xMn_xAl_5-xSi_xO₁₂（x=0.1-0.5）ceramics were analyzed from the aspects of ion occupancy,bond valence theory,P-V-L theory and oxygen polyhedron distortion.When x=0.2,the best microwave dielectric properties of ceramic samples were:ε_r=10.89,Q×f=56,135 GHz,τ_f=-39.35 ppm/℃.The Q×f values of ceramic samples were tested at different frequencies（@11 GHz,@16 GHz,@25 GHz）,and the results showed that the samples obtained the highest Q×f value of 88,200 GHz at 25 GHz.（3）The temperature coefficient of Y_2.9Mg_0.1Al_4.9Si_0.1O₁₂ garnet ceramics was adjusted by adding Ti O₂ with a large positive temperature coefficient.When 6wt%Ti O₂ was added,the temperature coefficient was close to zero,and the dielectric properties were as follows:ε_r=10.83,Q×f=13,457GHz,τ_f=-5.8 ppm/℃.The Wifi6E/7 microstrip patch antenna was designed based on the composite ceramic sample with near-zero temperature coefficient,and the center frequency of antenna remained constant after heating at 85℃.In addition,a dielectric resonator antenna applied in 5G millimeter wave band was designed using composite ceramic sample,which showed the application potential of garnet ceramics in dielectric substrates and dielectric resonators.