| The mobile communication terminal devices develop in the direction of intelligentialize and multi-function,the integration of product is higher and higher,all that due to the rapid development of mobile communication technology.So there is huge demand for internal antennas miniaturization of mobile phone.At present,the technology of mobile phone antennas miniaturization include short circuit,special substrate material,surface slotting and active network,etc.The magnetic materials were used for antennas substrate to study the effect of material for antenna miniaturization below the band of GSM1800 in this thesis.To obtain good permeability and high permeability cut-off frequency,the theories about two different crystal structures of Z-type and Y-type hexagonal ferrite were studied.First,the iron deficiency,Sr2?10?substitution,the amount of latent solvent?Bi203?,preparation technology conditions and Cr-doped have been investigated to analyze the impact on the phase structure,microstructure and electromagnetic properties of Z-type hexagonal ferrite material,the results have shown that the different factors have significant effects on permeability and permeability cut-off frequency.When the main composite is 3Ba0.7Sr0.3O·2Co O·10.8Fe2O3 with the amount of latent solvent of 3wt%,the sintering temperature of 1000?,Z-type hexagonal ferrite have electromagnetic parameters of?r?4.6,?r??0.19,?r?5.5,?r??0.01?1.5GHz?and?r?4.6,?r??0.36,?r?5.37,?r??0.012?1.8GHz?,besides,the permeability of Z-type hexagonal ferrite increase and the permeability cut-off frequency move to high frequency with the increasing of Cr-doped content.The next step is simply to study phase structure,microstructure and electromagnetic properties of Y-type hexagonal ferrite material,different sintering temperature have little influence on the performance of Y-type hexagonal ferrite material,electromagnetic parameters remain stable??r?2,?r??0.11,?r?9.53,?r??0.03 in the range of 0.5-4GHz?.The simulation works using HFSS software were performed at the last part of this thesis.To verify the theory that magnetic material can miniaturize antenna size,dipole antennas have been simulated,results show that magnetic material with different effective permeability and thickness have obvious effect on reducing the physical size of antennas.According to the above simulation results,we have done some simulation research about the lower frequency band of the antenna?GPS and GSM1800?which have been loaded two kinds of experiment materials,and found the radiation efficiency of antennas have been reduced due to the loss properties of the magnetic material,but can still content the actual use requirement.The center frequency of both two band antennas have shifted to lower frequency more than 130MHz,the physical size of antennas can be reduced ten percent,besides,with the increase of substrate thickness,size can be reduced to a greater degree,which further verified the effectiveness of magnetic substrate material for the miniaturization of antenna size. |
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