Study On Multiple Antenna Technology For Wireless Mobile Communication Terminal

With the development of wireless mobile communication technology and the innovation of communication system,the wireless mobile terminal,especially the smart phone,has profoundly influenced all aspects of people's life and became an indispensable part of people's life.Terminal antenna,a key component of personal wireless terminal equipment,directly affects the communication performance of terminal equipment and user experience,the design of which faces many challenges.First,the mobile terminal device develops towards miniaturization,multi-standards,whice requires terminal antenna to cover the frequency band of different communication standards;second,as the number of terminal antennas increases significantly,it is necessary to realize high isolation and low correlation between antennas in a limited space;third,with the increasing attention of radiation safety,the design of antenna needs to minimize the impact of antenna radiation on the human body.Therefore,in this thesis,the design of multi-standards the design of multi-antennas based on metal bezel structure,the design of terminal MIMO antennas based on mode elimination technique,and the SAR reduction of terminal antenna technique are studied respectively in view of the current demand of wireless mobile communication terminal antennas.The main contents of this thesis are arranged as follows:Firstly,it introduces the development process of wireless mobile communication technology and the characteristics of each generation of communication technique,summarizes the current situation of terminal antenna design research at home and abroad in recent years and clarifies a series of challenges faced by terminal antenna design including the miniaturization technique of terminal antenna,terminal multi-antenna decoupling technique and terminal antenna SAR reduction technique.Secondly,based on the metal bezel structure,a terminal multi-antennas system is designed for 4G/5G applications,including two parts,an antenna with small ground clearance covering 2/3/4G bands and a metal bezel slot MIMO antenna covering 5G bands.The test results show that the-6dB impedance bandwidth of the small ground clearance antenna are able to cover LTE700/2300/2500,GSM850/900/1800/1900 and UMTS2100 communication bands,and the antenna efficiency is greater than 50% and 40% in the low and mid-high frequency bands respectively.The metal bezel slot MIMO antennas are able to cover N78 communication bands,and the isolation is better than 15 dB between antennas,and the efficiency is greater than 72%.In addition,the radiation performance and MIMO performance of the designed antenna system are analyzed and discussed in terms of radiation pattern and envelope correlation coefficient.Then,the design of a dual-antennas pair is realized based on the mode-cancellation technique by compactly combining a bend-shaped loop antenna and a T-shaped monopole.High isolation of the dual-antennas pair can be achieved without loading of the decoupling structure by using anti-phase current coupling cancellation.Based on the proposed dual-antenna pair,the design of the eight-port MIMO antennas are completed,and the test results show that the designed dual-antennas pair works in the frequency band of N78 and N79 with isolation better than 35 dB and efficiency more than 70%.The isolation of the eight-port MIMO antennas are better than 12.7 dB.In addition,the radiation performance and MIMO performance of the antenna system are analyzed and discussed in terms of radiation pattern and envelope correlation coefficient.Finally,SAR reduction techniques for terminal antennas are investigated,including the SAR reduction technique based on branch loading and the SAR reduction technique based on ground character mode analysis.In the SAR reduction technique based on branch loading,by loading two branches around the reference monopole antenna,the 10 g body SAR at0.9GHz of the reference antenna is reduced from 1.46W/Kg to 0.95W/Kg,and the 10 g body SAR at 2.6GHz is reduced from 2.39W/Kg to 2.01W/Kg,achieving 35% and 16% SAR reduction.In the SAR reduction technique of ground character mode analysis,the ground character mode of the terminal is analyzed to optimize the antenna feed point position so as to realize the regulation of different eigenpatterns to achieve SAR reduction,and the 10 g body SAR of the antenna at 0.8GHz is reduced from 1.82W/Kg to 1.01W/Kg,achieving a SAR reduction effect of 44.5%.