Research On Multi-band Antennas For Mobile Terminals In Narrow-clearance Environment

With ultra-thin smartphones with full screens becoming the dominant trend,the clearance area inside the smartphone for antenna design is shrinking.In this way,not only the position of the antenna will be limited,the distance between the antenna and other metal structures will be closer.At the same time,the omni-directional communication performance of the antenna will be worse.Then,what can we do to realize the low profile and miniaturization of the antenna,and how to realize the multi-band and broadband coverage of the antenna.These problems that need to be solved are of great significance to the development of mobile terminals and are the main research direction of mobile antenna design.In view of the above requirements and challenges,this paper makes a research on the design of terminal antennas in narrow clearance environment.The main contributions are summarized as follows:Firstly,the research status and some difficult issues in the design of terminal antenna in narrow clearance environment are introduced.The common methods of realizing miniaturization and covering multiple bands of terminal antenna are analyzed and summarized,and applied flexibly to the irregular changing of clearance area,which is helpful to guide practical antenna design.Based on the previous investigation,three antenna schemes are proposed which are applied to narrow clearance environment.The first is a reconfigurable antenna with side-slit metal frame.The change rule,presented by the process of clearance reduction,is analyzed and summarized.The changes of antenna performance and parameters in different clearance environments are analyzed by simulation.The second antenna is a top-slit metal-frame antenna with a metal back cover.Generally,for a smart phone with metal frame,a plastic,ceramic or other non-metallic back cover or a "three-part" structure similar to the iPhone,are often used to achieve better radiation of antennas.However,in the second antenna structure,the entire metal frame is located directly above the metal back cover,and the entire structure has no clearance area from the top view.By reconfigurable technology,the coverage of seven frequency bands is realized successfully.In addition,with the rapid development of 5G communication in recent years,a number of mobile device manufacturers have added part of the sub-6G frequency bands to the issued 5G smartphone devices.Therefore,the third antenna structure is the Tri-band 8×8 MIMO antenna that can be applied to 5G mobile terminal system.In view of the current trend of narrow clearance,the 8×8 MIMO antenna have been positioned on both long sides of the smart phone,which leaves a lot of space for the design of 4G antennas and also avoid damaging the antenna performance.From the simulation and test results,the performance of proposed MIMO system is good enough to cope with the application of 5G in smartphone system in the future.