| The rapid development of modern science and technology promotes the continuous upgrading of mobile communication industry,and as a mobile communication essential,antenna plays a vital role in the signal transmission process.At present,the antenna with single function can be no longer adaptive to the new working scene,but the smart antenna can meet the needs of the latest development with the excellent characteristics of high communication quality and high spectrum utilization.Based on different application scenarios,four different smart antennas are designed in this thesis and the main work contents include:1.A wideband linearly polarized multimode smart antenna with eight ports is designed,which consists of eight pairs of elliptical dipoles and a hollow cylindrical metal reflector.It has 48.9%(2.90-4.78 GHz)impedance bandwidth,and there are two operating modes in the frequency band: one is the omnidirectional mode,that is,when all ports are added with the excitation of the same amplitude and phase,omnidirectional characteristics can be obtained in the horizontal plane;the second is the directional mode,that is,by adding the excitation optimized by the method of maximum power transmission efficiency(MMPTE)to the ports of antenna,single/multi-beam scanning can be realized in the horizontal plane.2.Considering the advantages of circular polarization,based on the first design concept,a wideband circularly polarized multimode smart antenna with eight ports is designed.It consists of eight pairs of square ring dipoles and a hollow cylindrical metal reflector.It has a52.1%(2.84-4.84 GHz)impedance bandwidth and 15.2%(3.29-3.83 GHz)axial ratio bandwidth.Both modes maintain circularly polarized characteristics.3.Considering the impact of the number of amplitude-phase adjustable ports on the cost of the array antenna,four one-two power dividers are added to the previous antenna,a wideband circularly polarized multimode smart antenna based on feed network with four ports is designed.It has 40.7%(2.85-4.31 GHz)impedance bandwidth and 13.5%(3.42-3.91 GHz)axial ratio bandwidth.It also has omnidirectional/directional circularly polarized working modes in the frequency band,only due to the reduction of the number of ports and the insertion loss caused by the power divider,the gain is reduced compared to the previous antenna.4.Different from the above three antennas,the fourth design is a wideband circularly polarized multimode smart antenna with six ports composed of omnidirectional and directional antennas with two different radiation types.It has a 25.2%(3.42-4.41 GHz)overlap impedance bandwidth and a 27.5%(2.88-3.80 GHz)axial ratio bandwidth.It is characterized by improving omnidirectional gain while preserving omnidirectional and directional dual-mode circular polarization.All of the four antennas work in the 5G operating frequency band promulgated by China and cover the n78 frequency band completely,which is in line with the development of 5G. |
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