| In order to meet the needs of high-speed broadband communication in the future,the fifth-generation mobile communication system(referred to as 5 G system)will work at higher frequencies to obtain greater bandwidth and achieve higher transmission rates.However,as the working frequency increases,the loss of electromagnetic waves penetrating the wall increases,which leads to the limitation of the indoor base station signal coverage indoors.Therefore,a large-scale indoor distribution system is required.As an integral part of the indoor distribution system,the antenna plays an important role in the whole system.However,the 5G indoor distribution system that can work in China's 3.45GHz and 4.9GHz frequency bands has few antennas and low gain,which is not suitable for practical applications.Therefore,based on the cross dipole antenna structure,this paper studies and designs a dual-frequency dual-polarized antenna array applied to China's 5G indoor distribution system.The main work completed includes:(1)A novel dual-frequency dual-polarized crossed dipole antenna structure is designed.The radiating element of the antenna consists of two pairs of fan-shaped corner-cut patches printed on the lower surface of the dielectric plate,and is coupled by the microstrip line on the surface of the dielectric plate.Feed excitation,dual-band operation is achieved by loading the branches.In order to avoid the two feeding microstrip lines overlapping each other,one of the conductor strips is adjusted to the lower surface of the dielectric plate,and the metallized vias are used to connect the microstrip lines on the surface of the dielectric board.Experiments show that the antenna has a reflection coefficient of less than-14 dB and an isolation of more than 22 dB in 3.27-3.6 GHz and 4.6-5.02 GHz.The gain in the low frequency band is about 8.3 dBi,the gain in the high frequency band is about 8.7 dBi,and the antenna pattern is stable.(2)To meet the high gain requirements,the above-described dual-frequency dual-polarized cross dipole antennas are combined into a 2 X 2 antenna array.The feed network of the antenna array is composed of three bisecting Wilkinson power splitters to achieve four equal power distribution.The experimental results show that the feed network has a reflection coefficient of less than-15 dB in 3-5.5 GHz and an insertion loss of about 6.5 dB.After combining the feed network with the antenna array,the reflection coefficient is less than-14 dB in the frequency range of 3.25-3.6 GHz and 4.6-5 GHz,the isolation is greater than 20 dB,and the low and high band gains are about 11 dBi and 13 dBi,respectively.(3)A dual-frequency dual-polarized crossed dipole antenna loaded with an artificial magnetic conductor structure is designed.The artificial magnetic conductor structure realizes dual-frequency zero-phase reflection by opening a slit in a square patch,and replaces the metal reflector to be loaded under the antenna,so that the antenna height is reduced by 27%.The results show that the antenna loaded with artificial magnetic conductor structure satisfies the reflection coefficient less than-14dB at 3.2-3.8GHz and 4.75-5.01GHz,the isolation is greater than 22dB,and the gains of low and high frequency bands are about 7dBi and 7.3dBi,respectively,and the pattern is stable.(4)A 2x2 array design is designed for the crossed dipole antenna loaded with the artificial magnetic conductor structure,and is fed by a Wilkinson power divider with a fourth power distribution.The test results show that the antenna array has a reflection coefficient of less than-14 dB in the bands of 3.1-3.6 GHz and 4.75-5.01 GHz,and the overall isolation is greater than 20 dB.The gains of the two bands are about 11.2 dBi and 13.5 dBi,respectively. |
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