| In recent years,interest in modern telecommunication systems has increased considerably.Ultra-high-speed local area networks（LAN）,cellphones,electronic toll booths（ETC）,millimeter wave applications and intelligent transportation systems（ITS）have raised the demand for microwave dielectric materials.In addition,the widespread use of portable and lightweight electronic devices has increased the demand for multifunctional,small,high-performance components.The MgTi/ZrTa2O8 ceramic materials with good microwave dielectric properties are promising for applications.In this thesis,the modification of MgTi/ZrTa2O8 ceramic system based on MgTi/ZrTa2O8 ceramic system is studied mainly by ion substitution as well as two-phase composite.In order to verify the practical value of the developed material,a rectangular microstrip patch antenna is designed from which MgTi0.6Zr0.4Ta2O8 is selected as the dielectric substrate.First,in order to adjust the resonant frequency temperature coefficients of MgTiTa2O8 ceramic materials,Nb5+ was used to replace Ta5+and Zr4+ ions to replace Ti4+,respectively,to investigate the effect of different ion substitutions on the MgTiTa2O8 The specific effects of different ion substitutions on the temperature coefficients of resonant frequencies of microwave dielectric ceramic materials were investigated.It was found that the Qf values of MgTi（Ta1-xNbx）2O8 system materials are mainly influenced by the material structure and also have a certain relationship with the density,and the optimal sintering temperature is reached at 1275℃,and the continued heating beyond the optimal sintering temperature will affect the grain growth leading to the decrease of the quality factor,and the temperature coefficient is mainly affected by the oxygen octahedral distortion.At 1275℃ sintering,MgTi（Ta1-xNbx）2O8 ceramics are sintered densely and the dielectric properties at this temperature are:εr=44.98,Q×f=16237 GHz,τf=+12.6 ppm/℃.Compared with Nb5+,Zr4+has a significant effect on the temperature coefficient regulation of this system,and as Zr4+becomes more and more,the ceramic material The existence of obvious structural changes indicates that the dielectric properties of the material of this system are mainly affected by the structural changes.From the physical phase analysis,it can be seen that at x=0.4 both trinitic rutile and monoclinic manganese-tungstenite structures exist,and the microwave dielectric properties parameters of MgTi0.6Zr0.4Ta2O8 ceramics at 1350℃ sintering temperature are:εr=31,Q×f=30544 GHz,τf=+9.6 ppm/℃.Thus,it can be concluded that Zr4+instead of Ti4+can regulate the temperature coefficient of τf without affecting other dielectric properties.Then the MgZrTa2O8 ceramic materials were subjected to A-site ion substitution,and Zn2+and Co2+with similar radii to Mg2+ were used for modification studies to investigate the relationship between different A-site ion substitution and MgZrTa2O8 ceramic materials,respectively.It was found that the XRD patterns of sintering at 1475℃showed that Zn2+did not affect the main structure of the ceramics of this system and no second phase was produced.The best densities of the Mg1-xZnxZrTa2O8 ceramics were obtained when the substitution amount was 0.04,and more pores were generated for x below or above this value,leading to the deterioration of the associated dielectric properties.From the relevant data obtained by refinement,it is concluded that the εr and Qf values are mainly affected by the porosity,while the τf value is mainly affected by the bond length as well as the bond valence.In 1475℃ sintered Mg1-xZnxZrTa2O8（x=0.04）samples,better microwave dielectric properties were obtained:εr=20.94,Q×f=125900 GHz,τf=-39.4 ppm/℃.Then,Mg1-xCoxZrTa2O8（0≤x≤0.09）microwave-dielectric ceramic materials were prepared and studied and analyzed,and it was concluded that From the analysis of XRD plots,it is concluded that Co2+substitution in the range of（0 ≤x ≤0.09）does not produce a second phase,and the dielectric properties of the material of this system are strongly influenced by the porosity,while the Qf value is influenced by both the relative density and the half height width（FWHM）together while the τf value is mainly influenced by the bond length as well as the bond valence The value of τf is mainly affected by the bond length and bond valence.In Mg1-xCoxZrTa2O8（x=0.04）samples sintered at 1475℃,good microwave dielectric properties were obtained:εr=21.56,Q ×f=122000 GHz,τf=-38.5 ppm/℃.For the above four groups of experiments,the MgTi0.6Zr0.4Ta2O8 ceramic with better performance is selected as the substrate material,and a rectangular microstrip antenna is designed on this basis,and the final size is determined as 8.8901 mm × 12.5 mm × 2 mm,and the microstrip patch antenna which meets the design expectation is obtained in this size,which has some practical application significance and is worthy of further study. |
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