Cordierite-based Ceramics With Ultra-low Dielectric Constant And Application Of 5G Prototype Antenna

With the rapid development of the 5th generation mobile networks（5G）and the Internet of Things technology,the demand and performance requirements for electronic information materials are also increasing.Microwave dielectric ceramics are widely applied in mobile base stations,satellite communications,military radar,GPS,bluetooth technology and other fields.Microwave dielectric ceramics with low dielectric constant,high Q value and stable temperature coefficient are important to future 5G technology.In this paper,ultra-low dielectric constant cordierite(Mg₂Al₄Si₅O₁₈)based microwave ceramics were synthesized via the solid-state reaction method.The detailed results are as follows:（1）Microwave dielectric properties of Mg_2-x(Li_0.5Ga_0.5)_xAl₄Si₅O₁₈（x=0-0.1）ceramics.Mg_2-x(Li_0.5Ga_0.5)_xAl₄Si₅O₁₈（x=0-0.1）ceramics were synthesized by the solid-state reaction.All the samples were identified as the cordierite solid solution.The relative permittivity of ceramics is mainly related to the ionicity,ionic polarizability,density and other factors,among which the ionicity of Mg-O bond has a greater effect than that of Al-O bond and Si-O bond.The lattice energy of the Si-O bond in the crystal structure is much greater than that of Mg-O bond and Al-O bond,the lattice energy of the Si-O bond,packing fraction and the symmetry of[Si₄Al₂O₆]ring have important contributions to the Q×f value.Theτ_f value of ceramics is mainly related to the bond energy,coefficient of thermal expansion and the distortion of[Mg O₆]octahedron.The bond energy of Al-O bond has the greatest impact on the temperature stability of the ceramics.When x=0.02,the microwave dielectric properties are:=4.72,Q×f=42,170GHz,τ_f=-29ppm/℃.（2）The microwave dielectric properties of Mg_1.8R_0.2Al₄Si₅O₁₈（R=Ca,Sr,Ba,Mn,Co,Ni,Cu,Zn）ceramics were systematically studied in this experiment.The relationship among the divalent element ionic properties,chemical bonds and crystal structures was investigated.The experimental results indicate that the relative dielectric constants of all components are between 4 and 6,which relate to the ionic polarizability of element R and the ionicity of chemical bonds.When R=Mn,Co,Ni,Cu,Zn,the values of Q×f andτ_f are better than those of R=Ca,Sr,Ba.The maximum value of Q×f is 61,880 when R=Ni,and the correspondingandτ_f value are 4.53and-32ppm/℃,respectively.（3）Temperature coefficient control,spectral study and 5G antenna integration for cordierite ceramics.In this experiment,theτ_f value of cordierite was adjusted by adding different mass fraction of Ti O₂.When x=5.5wt%,theτ_fvalue of ceramic was adjusted to-2.8 ppm/℃,and the correspondingand Q×f value are 5.24 and33,400GHz,respectively.Combined with the Kramers-Kronig（K-K）formula,the theoretical dielectric constant and dielectric loss of Mg₂Al₄Si₅O₁₈-x wt%Ti O₂（x=0,1.5,5.5）ceramics at microwave frequency band and terahertz frequency band were calculated by using the infrared beam line of the Hefei National Synchrotron Radiation Laboratory.The free space method was used to collect the dielectric constant and dielectric loss of Mg₂Al₄Si₅O₁₈-x wt%Ti O₂（x=0,1.5,5.5）ceramics in the terahertz frequency band.The simulated results are consistent with the measured results when x=5.5.Finally,the 5G patch antennas were designed and fabricated using Mg₂Al₄Si₅O₁₈-5.5wt%Ti O₂ ceramics with near zeroτ_f value as substrate.The measured center frequency was 5.86GHz,and the efficiency and gain are 76.3%and4.92d Bi,respectively.