Design Of Omnidirectional Dual Polarized Antenna Array And Polarization Reconfigurable Antenna Array

With the rapid development of mobile communication technology and the advent of 5G era,the requirements for mobile communication base station antenna are getting increasingly higher.For one thing,base station antennas are required to have omnidirectional radiation characteristics and high-gain characteristics;for another thing,because dual-polarized antennas have the characteristics of increasing channel capacity and realizing multiple-input multiple-output(MIMO)communication,omnidirectional dual-polarized antennas have become an important development direction in the future.In addition,since the polarization reconfigurable antenna can expand the application of antennas,this dissertation studies the design and implementation methods of high-performance omnidirectional dual-polarized antenna array and polarization reconfigurable omnidirectional antenna array operating in 5G communication frequency band of 3.5GHz,aiming at the 5G communication requirements for MIMO base station antenna.The main research contents and results are as follows:An omnidirectional horizontal/vertical dual-linearly polarized antenna is proposed and designed.The antenna consists of a printed loop antenna and a printed dipole antenna located at the center of the loop.The loop antenna radiates the omnidirectional horizontal polarized wave by loading the gap capacitance to make the current distributed on its surface uniform and in-phase.In order to reduce the size of the antenna,a folding dipole antenna is used to radiate omnidirectional vertical polarized waves.The results show that the antenna can achieve horizontal/vertical dual-polarized wave radiation,and under the two polarization states,the out-of-roundness of the pattern is ± 1.2dB,and the gain is about 3dBi.In the frequency band of 3.4 GHz to 3.6 GHz,good matching performance is obtained while|S11|<-20dB.An omnidirectional dual-linearly polarized 4-element antenna array is proposed and designed based on the omnidirectional horizontal/vertical dual-polarized antenna.According to the operating principle of the zero-degree phase-shifting metamaterial transmission line,a novel metamaterial series feed network based on a parallel-plate transmission line structure is proposed and designed.The size of the feed network is reduced by half in comparison with the traditional series feed network,and it has little effect on the radiation field of the antenna.The two metamaterial feed networks are used to feed the loop antenna array and the dipole antenna array in equal amplitude and in-phase respectively,to constitute an omnidirectional dual-polarized antenna array.The measured results show that in the frequency band of 3.4 GHz to 3.6 GHz while |S11|<-15dB,the antenna array can achieve horizontal/vertical dual-linearly polarized wave radiation.Under the two polarization states,the out-of-roundness of the pattern is ±2.5dB,and the gain is greater than 7dBi,which realizes the omnidirectional high-gain dual-linearly polarized radiation characteristics.Based on the omnidirectional horizontal/vertical dual-linearly polarized antenna array structure,an omnidirectional polarization reconfigurable antenna array is proposed and designed.By adding a radio frequency switch and a phase shifter to the feed network,the polarization reconfiguration of the antenna array is realized.The radio frequency switch controls the path of the feed signal by controlling the state of the diode,and the phase shifter is composed of a microstrip branch-line directional coupler.When the signal is fed through a branch with the phase shifter,the horizontal component has a 90° phase leading/lagging to the vertical component,thus the antenna radiates left-hand/right-hand circularly polarized electromagnetic waves;when the branch which the signal passes through does not have a phase shifter,the horizontal component has no phase difference with the vertical component,thus the antenna radiates horizontal/vertical polarized electromagnetic waves.Based on the theory and the simulation design results,the whole antenna feed system is fabricated and measured.The measured results show that the antenna feed system can realize the polarization reconfiguration between horizontal/vertical linear polarization and left-hand/right-hand circular polarization.And in each polarization mode,the gain of the antenna array is greater than 6.5dBi,and the out-of-roundness is±2.5dB.In the frequency band of 3.4 GHz to 3.6 GHz while |S11|<-15dB,the axial ratio(AR)of left-hand and right-hand circularly polarized waves is less than 3dB,which meets the design requirements.