Design Of Magnesium Silicate Based Microwave Dielectric Ceramics And Antenna For 5G Communication

People cannot live without communication technology.Today,the fifth generation（5G）wireless communication technology has become a hot research topic because of its high data transfer rate,low delay and large-scale connection.Microwave dielectric ceramics are the key materials to achieve high performance 5G equipment.For electronic devices used in 5G,ceramics are required to have low dielectric constant,low dielectric loss and near-zero temperature coefficient of resonant frequency.For the above requirements,magnesium silicate（MgSiO₃）,also known as enstatite,is considered to be a material with good application prospects due to its abundant raw materials,low cost,environmentally friendly,non-toxic,low dielectric constant and low dielectric loss,but it has multiple crystal structures and is prone to phase transformation,and there are issues such as high sintering temperature and difficulty in achieving density.To solve these problems,X-ray diffraction（XRD）and Scanning Electron Microscope（SEM）were used to discuss the synthesis conditions and the influence of Cu ion doping on the phase and microwave dielectric properties of MgSiO₃ ceramics,and the MgSiO₃-based 5G microstrip patch antenna was prepared,the details are as follows:（1）The influences of preparation conditions such as calcining temperature,calcining duration,non-stoichiometric and raw material particle size on the phase and microwave dielectric properties of MgSiO₃ ceramics were investigated.It was found that for the samples which use Mg O（150nm）and SiO₂（2μm）as raw materials,SiO₂,Mg₂SiO₄ and MgSiO₃（protoenstatite）appeared in the phase under different calcining temperatures（1250℃～1325℃）and calcining duration（5h～20h）.In the appropriate range,increasing the calcining duration can obtain the sample with higher content of MgSiO₃ than increasing the calcining temperature.The optimal calcining condition is 1300℃/10h,and theε_r of MgSiO₃ ceramics prepared under such conditions is 6.2,Q×f is 45300GHz andτ_f is-52.2ppm/℃.On this basis,non-stoichiometry has little effect on inhibiting the generation of the second phase,and the shift of non-stoichiometric points will lead to the increase of the second phase,and the increase of the content of the second phase will lead to the decline of microwave dielectric properties.Therefore,it is very important to keep the stoichiometric ratio of MgSiO₃preparation.Finally,Mg O（40nm）and SiO₂（15nm）with smaller particle size were used as raw materials.MgSiO₃ products containing a small amount of second phase can be obtained under the calcining condition of 1250℃/3h,and the sintered samples have better microwave dielectric properties:ε_r=6.6,Q×f=65800GHz,τ_f=-50.1ppm/℃.It is proved that for the MgSiO₃ system,the contact area between the materials with small particle size is larger,the diffusion distance is shorter,which can improve the completion of the reaction,reduce the existence of the second phase,and is conducive to the acquisition of excellent microwave dielectric properties of the ceramics finally.（2）Mg_1-xCu_xSiO₃（0≤x≤0.25）ceramics were synthesized by replacing Mg ions in MgSiO₃with Cu ions.When 0≤x≤0.15,the XRD diffraction peak shifts to the left with the increase of Cu doping amount,which is because Cu ion replaces Mg ion with smaller radius,leading to the increase of interplanar spacing.When x increases from 0.15 to 0.20,the XRD diffraction peak shifts to the right,and the crystal space group chang from pbcn to pbca through material matching and structural refinement.The interplanar spacing became smaller,resulting in rightward shift of diffraction peaks.When x>0.2,Cu ions continue to replace Mg ions and the space group remains pbca,the diffraction peak shifts to the left.It is also found that copper ion doping can inhibit the phase transition of the ceramics at room temperature.XRD analysis of MgSiO₃ and Mg_0.95Cu_0.05SiO₃ samples before and after 1 year of placement show that MgSiO₃ samples had phase transition,while Mg_0.95Cu_0.05SiO₃ samples has no phase transition,which indicates that Cu ion substitution can inhibit the phase transition of MgSiO₃ for a long time.Theε_r of doped ceramics increases with the increase of doping amount,and the distortion degree of[Mg（2）O6]octahedron shows an opposite trend.The Q×f is mainly affected by non-intrinsic loss,and liquid phase and cracks appear in the process of ceramic preparation,which seriously increases the dielectric loss of the sample.In addition,it is found that CuO can reduce the sintering temperature of ceramics from1400℃to 1125℃～1325℃and broaden the sintering interval from 50℃to 100℃.The best microwave dielectric properties of the Cu-substituted ceramics were obtained by sintering Mg_0.95Cu_0.05SiO₃ at 1325℃for 5h,and the microwave dielectric properties areε_r=6.2,Q×f=93600GHz,τf=-33.7ppm/℃.（3）Two 5G patch antennas were fabricated using Mg_0.95Cu_0.05SiO₃（MCS）and MgSiO₃（MS）microwave dielectric ceramics as substrate.A simulation model was established according to the above two materials,and then two microstrip patch antennas with the same size was made according to the same simulation model using the above two materials.Finally,the performance of the antenna was tested.The antenna parameters obtained by CST software simulation are as follows:operating frequency is 4.7GHz,bandwidth is 258MHz,and S11 is-26.23d B.The actual measured center frequency of MCS based antenna is 4.66GHz,bandwidth is 150MHz,and S11 is-23.96d B;the center frequency of MS based antenna is 4.71GHz,bandwidth is 165MHz,and S11 is-22.7d B.A year later,it was tested again,and it was found that the performance of MCS based antenna changed little,while the MS-based antenna partially cracked,resulting in its S11 greater than-10d B,which could not meet the practical application requirements of the antenna.This shows that the use of Cu ion doped MgSiO₃ based ceramics as the substrate material of 5G antenna can ensure the reliability and stability of antenna performance,which shows the potential of such materials in practical applications.