| In recent years,the rapid development of wireless mobile communication has increased the demand for data transmission speed and channel capacity of mobile communication systems,and scarce spectrum resources have increasingly become a constraint to the development of mobile communication.On the one hand,MIMO(Multiple-Input Multiple-Output)technology can greatly improve the data transmission rate and complexity in a complex multipath environment without additional frequency bandwidth and transmission power,which has become the core technology of the fourth generation mobile communication(4G)and the fifth generation mobile communication(5G).On the other hand,compared with the current 2G / 3G / 4G wireless communication systems,5G communication systems have the advantages of high speed,low delay,high reliability,and fast access,and there has a large number of spectrum resources,which can alleviate the scarcity of spectrum resources.As an important component of terminal device,the design and research of MIMO antennas for 5G mobile phone has become a research focus for scholars at home and abroad.With the development of smart phones toward miniaturization and full-screen,the clearance reserved for antenna design and multi-antenna placement is becoming more and more limited.Placing multiple antennas in a limited space will generate strong electromagnetic coupling,which will affect the original current distribution on the antenna and thus affects the performance of the antenna.Therefore,it is more and more important to study the decoupling technologies in MIMO antennas for 5G mobile phone.This paper focuses on the decoupling technologies of MIMO antennas and it presents several MIMO antennas with high isolation.1.The idea of compensation network decoupling method is proposed.Taking the neutralization line as an example of the compensation network,it is analyzed how the compensation network decoupling technology guides designing MIMO antenna to achieve high isolation.First,an ultra-wideband inverted F antenna is designed,where both the meander feedline and the inverted F patch operate together to realize the characteristic of three-mode resonance,which broadens the bandwidth of the antenna and the impedance bandwidth can cover 3.3-6.0GHz.Then,based on the antenna element,the effect of inductive neutralization line,capacitive neutralization line and coupled neutralization line on the isolation enhancement is analyzed.2.The idea and structure of reconfigurable network with T-shaped neutralization line are proposed.According to the characteristics of different antenna elements,different lumped elements on the neutralization line are selected to achieve decoupling during the required frequency band.Designing a simple antenna with single frequency,and with reconfigurable Tshaped neutralization line as the structure of the compensation network,adopting the guideline of the compensation network decoupling method to design two two-element MIMO antennas and a cascade four-element MIMO antenna based on single-frequency antenna elements,the simulated and measured results show that three MIMO antennas have good isolation characteristics.Therefore,reconfigurable T-shaped neutralization line is feasible in achieving decoupling between MIMO antenna elements.3.Design a dual-frequency antenna,which is developed from a meander monopole antenna with direct feed and an inverted L grounding patch with coupled feed.And it has dual-frequency resonance characteristics,and the impedance bandwidth is 3.3-5.5 GHz.Based on the antenna element,a two-element MIMO antenna with broadband decoupling is designed adopting the reconfigurable T-shaped neutralization line proposed in the previous chapter as the structure of the compensation network.Finally,on the basis of the MIMO antenna,the grounding branchs of two antenna element and the neutralization line are merged to achieve the miniaturization of the MIMO antenna structure.Measured results show that the size of the MIMO antenna is reduced by 11.4%,and it still has high isolation characteristics.Once again the feasibility of reconfigurable T-shaped neutralization line on decoupling is verified.4.The above MIMO antennas are all designed adopting the compensation network decoupling method,and this chapter introduces the idea of adopting the compact field decoupling method to design MIMO antennas with high isolation.Based on the ultra-wideband inverted-F antenna proposed above,a MIMO antenna with compact-field self-decoupling characteristics is designed.Simulated and measured results show that the MIMO antenna has good isolation over the operating frequency band. |
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