Low Temperature Co-fired Mg-based Magnetic And Dielectric Electromagnetic Materials And Their Basic Research On Antenna Application

Microstrip antenna is the inevitable choice to realize a 5G communication system with high precision,miniaturization,integration,multi-functionality,and high speed.As a new class of integrated components,microstrip antenna can be involved in signal detection and electromagnetic wave radiation in mobile phones and base stations.At present,very high frequency?VHF?antennas based on the low-temperature co-firing ferrite?LTCF?technology have a significant market worldwide.However,this field of research still has several unsolved technical problems,primarily with respect to the development of new materials,LTCF antenna miniaturization,antenna gain improvement,and antenna bandwidth enhancement.From a comprehensive point of view,the realization of antenna miniaturization,control of the dielectric constant of the antenna substrate material,matching of the permeability and permittivity of the substrate material?the permeability is almost equal to permittivity?,and wideband at high frequency are the current research topics of interest.Among them,the research and development of antenna substrate materials with equal permeability and permittivity is especially important;the realization of this phenomenon for a very wide frequency band with low magnetic and dielectric loss has not yet been achieved.To resolve this problem,low-temperature sintered Mg ferrites were chosen as the research object in this study to be designed as antenna substrate materials;the mechanism of the influence of A and B sites ion substitution on the microstructure,and high-frequency magnetic and dielectric properties of the antenna were studied.Subsequently,high cut-off frequency Mg-based LTCF antenna substrate materials were prepared.Finally,based on the substrate materials,we designed,simulated,and adopted LTCF technology to process microstrip circularly polarized antenna.The agreement between the simulation and processing test results verified the feasibility of the proposed materials applied in the VHF antennas.The specifics of the study are as follows:First,the effects of A-site Cd²⁺ion substitution on high-frequency magnetic and dielectric properties of spinel Mg and MgCo ferrites were studied.The amount of Cd²⁺ion substituted was varied,and the ferrites were low-temperature?<960??sintered by adding Bi₂O₃ as the sintering aid.The results showed that the magnetic properties could be enhanced by introducing Cd²⁺ion at.When the optimum substitution amount of Cd²⁺ion was 0.15?stoichiometric proportion?,Mg ferrites sintered at 910?with 0.25 wt.%Bi₂O₃ showed the saturation magnetization Ms=38 emu/g,and coercivity Hc=70.88 Oe.In the frequency range of 1–150MHz,the real part of the permeability and dielectric constant were nearly equal??'??'?25?,and the cut-off frequency f_r was approximately200 MHz.Simultaneously,the sample under low-temperature sintering possessed relatively low magnetic loss(?10^-2)and dielectric loss(?10^-3).Then,the effect of Cd²⁺ion substitution on MgCo ferrites was studied.The results showed that the the magnetic properties of the ferrites were enhanced to some extent.When the substitution amount was 0.4,the average grain size was approximately 2.8?m,Ms of the sample was approximately 40 emu/g,Hc was 65 Oe,and?'and?'of the sample had a greater value than those of substituted Mg Cd ferrites;in addition to the values of?'and?'being close to each other??26?and low dielectric loss,the larger values of?'and?'indicate a higher miniaturization factor,which is favorable for materials used as antenna substrates.Secondly,based on the aforementioned results,the effect of the substitution of Fe³⁺ions at the B-site on the high-frequency magnetic–dielectric properties of Mg_0.8Cd_0.2Fe₂O₄ ferrites was symmetrically studied to explore antenna substrate materials with higher frequency and better high-frequency magnetic–dielectric properties.Sm³⁺ions were selected as substitutes for Fe³⁺at the B-site.The results showed that with the increase in the substitution amount,the magnetic properties were enhanced first and then weakened,and the dielectric properties exhibited slight changes.In this way,the magnetic and dielectric properties of Mg ferrite were dynamically regulated.Finally,when the substitution amount of Sm³⁺ion was 0.1(Mg_0.8Cd_0.2Fe_1.9Sm_0.1O₄),the sample still achieved matching magnetic–dielectric properties??'??'?25?.Compared with the result of A-site Cd²⁺substitution,the loss of the sample was slightly reduced,and the cut-off frequency was increased.In addition,the Sm³⁺ions substitution at the B-site was replaced by Ga³⁺ions.The results can be summarized as follows:?1?Ga³⁺occupied the B-site,resulting in enhanced superexchange interaction between A and B sites;hence the magnetic properties were enhanced.The introduction of Ga³⁺ions also resulted in the formation of Ga Fe O₃,which had multiferroic properties and improved the magnetic properties.?2?After the substitution,the application frequency of the sample increased,the cut-off frequency of the permeability was approximately 300 MHz;the magnetic and dielectric performance at 200 MHz were as follows:?'=25,the order of tan??was in the range of10^-4–10^-3,?'=30,tan??has order of 10^-2.The normalized impedance of the materials was still close to 1,which can greatly improve the working frequency without decreasing the values of?'and?'.The optimum sintering temperature was 915?.The sample structure was relatively dense at this temperature,and the grain size was moderate and uniform.In the frequency range of 1–200 MHz,the permeability was 40,the dielectric constant was 25,the impedance was 1.4,and the broadband factor was0.002.Finally,based on the ferrite ceramics substituted by Ga³⁺ions,a wideband circular polarized microstrip patch antenna with a resonance frequency of 300 MHz was designed.The material was processed into a smooth antenna substrate by LTCF technology.Then the simulated antenna was processed using screen-printing technology and sintered at 880?.Finally,in microwave darkroom,the measurement was performed,and results showed that:?1?the impedance of the antenna had realized a relatively wide bandwidth,ranging from 270 MHz to 330 MHz?relative bandwidth was20%?,the directional coefficient of the antenna was high?maximum directional coefficient of 3.87 d B?.In the theta range of 110°–140°,the axial ratio was less than 3d B,with the smallest value being 1.4 d B;this indicates excellent circular polarization performance for the processed antenna.?2?There was almost no difference between the simulated and measured results,which verified the feasibility of applying the studied substrate material to the VHF antenna.