| Nowadays,the development of 4G mobile communication technology has tended to mature,and 5G mobile communication technology will become the core of development.In the complex electromagnetic environment of modern base stations,the coexistence of 4G and5G is the first problem to be faced.Secondly,the internal antennas must have excellent radiation performance to resistance the electromagnetic interference.The Ministry of Industry and Information Technology announced the 5G frequency band of operators in 2018,and determined 3400～3600MHz and 4800～4900MHz as the 5G test frequency band.It is necessary to first design 4G and 5G antennas with low profile according to the base station space to realize the coexistence of 4G and 5G in the limited base station space,and then solve the cross-frequency mutual coupling and occlusion effect caused by the fusion of high and low frequency antennas.Moreover,to realize remote information transmission,the antennas must have high gain and stable beamwidth.This paper summarizes the development trends of base station antennas at home and overseas and the application of Characteristic Mode Theory in antennas.At the same time,combining with the relevant knowledge of antenna theory and the scientific research projects during the graduate period,the broadband base station antennas in the 4G and 5G frequency bands and the characteristic mode analysis method are deeply studied.The main research contents are as follows:(1)Based on the characteristic mode analysis method,a broadband base station antenna operating in the Sub-6 GHz band(3300～3600 MHz,4800～4900 MHz)is proposed.The antenna consists of two pairs of printed fan-shaped dipoles,reflectors and microstrip stubs.The two pairs of dipoles are printed on the bottom of the dielectric plate and placed perpendicular to each other to realize dual polarization.Through characteristic mode analysis,the radiation mechanism of the initial antenna is understood in detail.In combination with the ideal mode characteristic current distribution,the appropriate slot position is selected to etch the rectangular narrow slot on the sector dipole to increase the resonant mode of the antenna and obtain the final antenna.The rationality of the Y-shaped microstrip feeder stub position is verified by analyzing the antenna modal weighting coefficient(MWC).(2)Aiming at the high radiation index requirements of base station antennas in the complex electromagnetic environment of modern base stations,a broadband high isolation base station antenna operating in 4G and some IMT bands is proposed using Barron feed technology.To improve the impedance matching of the original antenna,the irregular inverted L-shaped slot is introduced on each radiation patch.Furthermore,the characteristic mode analysis method is applied to optimize the mode distribution of the antenna and realize the low profile design by loading the frequency select the surface structure above the antenna.(3)Aiming at the two key parameters of the front-to-back ratio and half-power beam width of 4G/5G base station antennas.From the theoretical level,find out the key points to improve the front-to-back ratio and half-power beam width,and creatively propose a parasitic wave suppression fence structure,which is symmetrically placed around the antenna.The introduction of fence structure effectively suppresses the radiation of diffraction electromagnetic wave,and introduces vertical current around the antenna without increasing the physical size of the antenna.The FBR and HPBW of the proposed antenna are respectivily increased by 6 d B andafter the introduction of fence structure.The FBR of the proposed antenna is more than 22 d B,and the average HPBW is 85 in the whole working band.Therefore,the proposed fence structure has certain practical value for improving the radiation performance of 4G/5G base station antenna. |
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