Study On PTFE Based High Frequency Composite Dielectric Materials And Its Application On Filters

With the development of 5G technology,a wave of communication infrastructure construction upsurge has been set off in the world,and the demand for microwave devices for manufacturing communication equipment has greatly increased.5G technology has more stringent requirements for the performance of microwave devices,and higher requirements for the reliability and stability of the device itself.At present,the Miniaturized Microwave Filter for 5g base station is mainly based on microwave ceramic materials with high dielectric constant and low loss,which have excellent electrical properties,but there are also some problems,such as the sintering process is easy to cause the size of the same batch of products is uneven,and the hardness of materials makes them difficult to process.The composite material has the advantages of easy processing,light weight and good affinity with polymer.The preparation of composite material with high dielectric constant and low loss can make up for the shortage of ceramic material,which has strong application potential.In this paper,we try to improve the traditional composite material with low dielectric constant and large dielectric loss,and give full play to its advantages.Firstly,several groups of CaTiO3/PTFE（polytetrafluoroethylene）composites and CCTO/PTFE composites with different mass fractions were prepared,and the properties of the two composites were tested and compared.The results show that although the low-frequency dielectric constant of CCTO is much higher than that of CaTiO₃,the properties of the composites prepared by CCTO as fillers are seriously deteriorated in the microwave frequency band,and the dielectric properties are not as good as that of CaTiO₃.When the mass fraction of CaTiO₃is 64wt%,the high frequency（>1 GHz）dielectric property is the best.At this time,the high frequency dielectric constant is 15.48,and the loss is slightly less than 5×10^-3.The dielectric constant of the composite is predicted by the theoretical model and compared with the experimental results.It is found that the EMT（effective medium theory）model and the modified logarithmic model are more similar to the experimental results.On this basis,we attempt to introduce conductors as the third phase into two-phase composites.Graphite,MWCNT（multi-walled carbon nanotubes）and nano-silver powder as the third phase were prepared and tested.The core-satellite structure commonly used for energy storage materials has been innovatively applied to dielectric materials:a core-satellite structure CaTiO₃@Ag/PTFE composite was prepared by in situ reduction with well-dispersed nano-silver particles introduced into the ceramic/polymer composite system.Its high frequency dielectric constant reaches 19.23,while its loss is only 4.83×10^-3.The dielectric constant is close to that of ceramic materials which are commonly used in filters at present.Meanwhile,a series of dielectric filters with a center frequency of 3.5 G Hz and a return loss of>20 d B were designed by using the PTFE composite.The out of band suppression ability of the filter is optimized.The rectangular coefficient of the optimized cross coupled four cavity filter is only 1.965,which realizes the strong out of band suppression ability.It fully verifies the application potential of polytetrafluoroethylene composite in the field of microwave communication.