| Nowadays,all countries in the world are carrying out infrastructure construction of the fifth-generation(5G)communication technology.5G communication systems are increasing the rate of information transmission.Multiple In Multiple Out(MIMO)antennas of mobile terminals closely related to the transmission rate are particularly important.The development of mobile phone terminals shows ultra-thin,narrow borders,long standby,and other multi-functional development trends,making the mobile phone reserved for the antenna clearance area is getting smaller and smaller.Besides,mobile terminals also need to cover multiple working frequency bands of 5G below 6GHz,and several multi-band antennas need to be placed in a narrow space,making the design of mobile terminal MIMO antennas full of challenges.Given the above design difficulties,this article deeply studies the design of MIMO antennas for mobile terminals.The main work includes: designing three kinds of MIMO antenna systems for mobile terminals,the first two types apply to Chinese 5G operating frequency band,while the last one applies to Europe's 5G operating frequency band.The three antennas are all suitable for 5G mobile phones with 5.5-inch screens.The first type of antenna uses a double U-shaped ring structure as the antenna unit,and the reflection coefficient in the working frequency bands 3.3-3.4 GHz,3.4-3.6 GHz,and 4.8-5.0 GHz is less than-10 d B.The decoupling of the floor support is used to improve the isolation between the antenna units.The isolation of the antenna in the operating frequency band is greater than 15 d B,and the principle of decoupling of the floor support is analyzed.The antenna's performance parameters such as directivity,efficiency,envelope correlation coefficient,and channel capacity all meet the design requirements of 5G terminal antennas.By loading a MIMO antenna with a hand model simulation,the performance of the terminal antenna in the actual application is simulated.The basic element of the second type of antenna consists of a monopole and loop antenna.The reflection coefficient of the antenna in the operating frequency bands 3.3-3.4 GHz,3.4-3.6 GHz,and 4.8-5.0 GHz is less than-6 d B.The introduction of neutral line decoupling reduces the coupling between the antenna elements.The simulation results show that the isolation of the MIMO antenna in the operating frequency band is greater than 10 d B.The directivity of the antenna is omnidirectional,the efficiency in the working frequency band is greater than 40%,the envelope correlation coefficient is less than 0.09,the requirements of the terminal antenna for the envelope correlation coefficient are less than 0.5,and the channel capacity is 34.8-38.2bps/Hz.The simulation of loading a MIMO antenna with a manual model shows that the efficiency of the antenna has decreased because the manual model is a high-loss media.Simulation results show that the antenna completely meets the performance specifications of 5G terminal antennas.The third type is an 8-port ultra-wideband MIMO antenna.The antenna element uses a coupling loop structure,and a single element consists of four radiating structures.Through simulating optimization,the antenna can cover the 5G working frequency bands(3.3-5.0GHz)of countries in Europe and other regions.The isolation of the antenna in the whole frequency band is greater than 13 d B,and the efficiency is greater than 60%.The envelope correlation coefficient of the antenna in the working frequency band is less than 0.07,and the average channel capacity is 35.5bps/Hz.Finally,the performance of the MIMO antenna by loading the hand model is studied,and the related results are analyzed. |
