Study Of Dielectric Properties And Applications Of Low Loss Li₃Mg₂NbO₆ Microwave Ceramics

Since the rapid development of mobile communication technology,filters,resonators,microwave oscillators and other key components in communication system restrict the development of microwave communication.As the key material of microwave devices,the research on modification of microwave dielectric ceramics is very significant.Li₃Mg₂Nb O₆ is a kind of microwave dielectric ceramics with excellent dielectric properties.In thesis,the restriction relationship between the dielectric properties of microwave dielectric ceramic materials is deeply explored,and ceramics are prepared by traditional solid-phase method.In order to improve the quality factor and temperature stability of ceramics and reduce the sintering temperature,a low sintering temperature,a high quality factor and a resonant frequency temperature coefficient close to zero were obtained by using ion substitution and adding combustion aid.Through X-ray diffractometer,scanning electron microscope,vector network analyzer and other characterization analysis of ceramics,the following research results are obtained:（1）Using Ge⁴⁺ion to replace Nb⁵⁺ion,and Li⁺ion could keep electricity price balance and improve the dielectric properties of ceramics.Li_3+xMg₂NB_1-xGe_xO₆（x=0,0.02,0.04,0.06,0.08）ceramics were prepared by traditional solid-state method.The results show that there is no second phase in the XRD pattern.The ionic doping increases the average grain size,volume density and dielectric constant of ceramics,and improves the quality factor and temperature stability of ceramics.The dielectric properties of Li_3.02Mg₂Nb_0.98Ge_0.02O₆ ceramics prepared at 1250℃ are:ε_r=15.32,Q×?=96988GHz,τ_?=-8.25ppm/℃.（2）Using Ti⁴⁺ion instead of Nb⁵⁺ion,and using Li⁺ion to maintain electricity price,at 1050℃ sintering temperature,the prepared Li_3.06Mg₂Nb_0.94Ti_0.06O₆ ceramics has the best performance:ε_r=15.48,Q×?=122972GHz,τ_?=+5.7ppm/℃.（3）Using Ga³⁺ion instead of Nb⁵⁺ion,and using Li⁺ion to maintain electricity price,at 1200℃ sintering temperature,the prepared Li_3.12Mg₂Nb_0.94Ga_0.06O₆ ceramics has the best performance:ε_r=15.32,Q×?=81701GHz,τ_?=-6.8ppm/℃.（4）In order to reduce the sintering temperature of ceramics,V₂O₅ was added to the ceramics after pre-firing as a firing aid.On the basis of reducing the sintering temperature of ceramics,appropriate amount of second phase Ti O₂ was added as a pin to improve the ceramic crystallization process,making the grains more uniform and better dielectric properties.At 925℃,the best performance of Li₃Mg₂Nb O₆-1wt%V₂O₅-4 wt%Ti O₂ ceramics is:ε_r=14.85,Q×?=54968GHz,τ_?=-1.1ppm/℃.（5）The microstrip patch antenna of microwave communication was modeled and simulated by HFSS software and ceramic substrate.The results show that at the resonant frequency of 9.7GHz,the value of S₁₁ is-14.90d B,and the normalized input impedance is（1.243-J0.327）ohm.Near the resonant frequency,the voltage standing wave ratio is less than 1.69,and the maximum gain is 4.75dB.