| With the development of wireless communications,the fifth-generation(5G)mobile communications networks with high speed,large capacity and low latency have been widely concerned by telecom operators and research institutions all over the world.Massive MIMO(Multiple input multiple output)technology has also been extensively studied as an important technology for 5G communications.For the common MIMO technology,only a few antennas are usually needed on the base station,which is mainly used to obtain diversity gain and multiplex gain.The research and application of this technology have been improved.Massive MIMO technology can not only fully utilize multipath effects but also depress the fading,noise and interference,and reduce the nonlinear design in signal processing system by placing hundreds of antennas on the base station,so as to increase the system capacity.By introducing other techniques,such as beamforming,the spatial multiplex gain can be fully improved,interference can be further reduced,and more terminals can be served at the same time.In order to place such a large number of antennas in a limited space,it is necessary to reduce the element size,element spacing,and ensure high isolation between the elements at the same time.Compact massive MIMO antennas are studied in this thesis,and the main contents are as follows:In Chapter 1,research background,significance of massive MIMO antennas and common decoupling methods for MIMO antennas are mainly introduced.At the same time,research progress of massive MIMO antennas is presented as well.In Chapter 2,MIMO technologies and the parameters that need to be considered when designing MIMO antennas are mainly introduced.In Chapter 3,design of a compact single-polarization massive MIMO antenna,including the antenna design and the mushroom-type EBG isolation structure design,is introduced.The mushroom-type EBG structure can be used to suppress the surface waves.Therefore,the distribution of surface wave electromagnetic fields is depicted first,and the operation mechanism and the simulation method of mushroom-type EBG structure are introduced next.Due to the narrow element spacing,mutual coupling is very strong.Considering the fact that the space between the antenna elements is long and narrow,we extend the ordinary mushroom-type isolation structure along the longitudinal direction and move the short-circuit pin to one end to form a slender mushroom-type isolation structure.Simulation results show that with the slender mushroom-type EBG isolation structure,isolation between the single-polarization 1×4 MIMO antenna elements is enhanced to greater than 15 dB.A comparison of simulation and measurement data verifies this design.Compared with the expanded MIMO antennas of 1×8 and 4×4,the single-polarization 1×4 MIMO antenna has been proved to be able to expanded into a massive MIMO antenna.In Chapter 4,design of a compact dual-polarization massive MIMO antenna is described.Design of the dual-polarization antenna element is introduced firstly;a 1×4 MIMO antenna consists of four such antenna elements is designed next.Isolation is improved by loading the slender mushroom-type isolation structure.The results of simulation and measurement are in good agreement.By comparing with the expanded 1×8 and 4×4 MIMO antennas,it is proved that the dual-polarization 1×4 MIMO antenna can be expanded into a massive MIMO antenna.In Chapter 5,the work of the thesis is summarized,the deficiencies of the designed antennas are pointed out,and the follow-up work is prospected. |
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