Research On Different Frequency Decoupling Technology Of Mobile Communication Base Station Antenna

With the rapid development of modern communication system,5G（the fifth generation communication technology）has entered large-scale commerce,which puts forward higher requirements for mobile communication system,such as high rate,low delay,low cost,large capacity and so on.The popularity of 5G does not mean that the existing 2G/3G/4G systems should be abandoned,but that multiple systems need to coexist for a long time to meet different needs.However,the addition of new frequency bands will introduce new antenna units,resulting in more congestion in the already limited space.When the antennas of different working frequency bands are placed in close proximity,the different frequency coupling between antennas will bring impedance mismatch,deterioration of isolation and pattern distortion.Therefore,how to realize different frequency decoupling has become a difficult and hot spot in the research of multi frequency mobile base station antenna.The main research focuses on the problem of different frequency decoupling of dual band base station antenna.The specific content is divided into the following three aspects:Firstly,a design method of folded structure and parasitic branches originally used in patch antenna are uesd in all metal antenna to realize the broadband miniaturization of dual polarization base station antenna is proposed.Starting from the resonance characteristics of cross ring dipole,this paper designs the radiation unit into a folded structure to increase the current path,so as to realize the miniaturization of antenna unit.The size of the antenna unit plane is reduced by 63.4%from 0.97λ₀×0.8λ₀（λ₀corresponds to the center frequency point820MHz）reduced to 0.53λ₀×0.53λ₀By introducing parasitic branches and adding new resonant frequency points,the working bandwidth of the antenna can reach 43%（650～1000MHz）.The simulation results show that the antenna designed not only realizes broadband miniaturization,but also has stable pattern and gain.Secondly,the structures of filter and harmonic suppression are combined to suppress the inductive coupling and resonant coupling in different frequency coupling.For inductive coupling,a filter structure is loaded in the low-frequency radiation unit to reduce the high-frequency induced current in the low-frequency and improve the pattern gain of the high-frequency antenna;For resonant coupling,ferrite coils are loaded on the high-frequency feed coaxial to suppress the low-frequency common mode resonant current and improve the low-frequency radiation pattern and port isolation.The simulation results show that after loading the filter structure and harmonic suppression structure,the port isolation between high and low frequency antennas is improved by 10d B.The gain of high frequency band and low frequency band is9.3±2d Biand 8.3±2.4d Birespectively,and the 3d B beam width of H plane is64.5°±4°and65°±4.5°respectively.Thirdly,a new broadband frequency selection surface is designed to improve the pattern of dual-band base station antenna with small frequency ration.Limited by the working bandwidth of the frequency selective surface,the traditional frequency selective surface is only suitable for dual band base station antennas with high frequency ratio.The circular ring frequency selective surface designed in this paper has simple structure and can be applied to dual band base station antenna with small frequency ratio.The simulation results show that the dual band（690～960MHz,1700～2700MHz）base station antenna array with frequency selective surface has low coupling between high and low frequency antennas,and the pattern gain meets the index requirements of base station antenna array in their respective working frequency bands.