Research On Decoupling Of High-isolation Compact MIMO Antennas

With the commercialization of 5G at the end of 2019,5G communication technology is developing rapidly.This technology theoretically has the advantages of high speed and low latency,which greatly increases users' demand for wireless network capacity and network reliability.However,it also brings many problems that are difficult to solve with traditional methods,which brings great challenges to the design of mobile terminal antennas and base station antennas.As terminal devices become thinner and lighter,the design space for antennas becomes smaller and smaller.How to design miniaturized terminal antennas,how to accommodate more antennas in a limited space,and how to improve the port isolation between multiple antennas have become a hot issue in terminal antenna design.Correspondingly,in order to cope with the increase in communication capacity and the shortage of space resources,more base station antenna arrays will be placed in the original space,which will deteriorate the port isolation of the antenna and the radiation parameters.How to solve these problems is also a difficult point in the industry.This paper is suitable for the decoupling research of small element MIMO mobile phone antennas and base station antenna arrays.Several high-isolation MIMO mobile phone antennas have been designed using different decoupling methods,and by designing a new base station element,the isolation between the base station antenna arrays is improved,The main contribution of the dissertation can be summarized as follows:1.A method to improve the isolation of the antenna by using the coupling neutralization line,the T-type coupling neutralization line,and coupling neutral lines loaded with lumped elements is proposed.First,design the frame antenna that works in the N78(3400-3600 MHZ)frequency band,and using the first two methods improves the isolation of the two-element MIMO antennas arranged on both sides of the floor and on the same side.The two arrangements are then summarized to obtain a four-element MIMO antenna.Its arrangement is similar to the Chinese character "?".The T-type coupling neutralization line and the coupling neutralization line with lumped elements are used for improving the isolation between the elements,and finally the isolation between the four-elements compactly arranged antennas is greater than13 d B,which realizes placing more antennas in a small space while maintaining high isolation between antennas.2.By analyzing the current distribution and radiation characteristics of the antenna elements,two self-isolated two-element MIMO antenna structures on both sides of the floor are proposed.The isolation of the two structures in the N78 frequency band has reached 13 d B and18 d B respectively.By analyzing the second structure,the number of ports has been doubled and expanded into a four-port shared radiator MIMO antenna under the original radiator size.Adjust the inductance on the radiator,finally the isolation of the four-port shared radiator MIMO antenna in the N78 frequency band is greater than 13 d B.3.The base station antennas working in the same frequency band are placed horizontally and close,the port isolation is poor.To solve this problem,it is easy to think of transforming the base station antenna into a cavity-backed base station antenna.In theory,it can ensure the stability of the antenna element itself and improve the isolation between the elements.However,the edge of the cavity is close to the radiator,the coupling current on it is too strong,resulting in poor antenna radiation parameters.At the same time,due to the current coupling between the cavities,the isolation between the cells is improved very little.Using the idea of 1/4? choke sleeve,a choke back cavity base station antenna that works at 1850-2400 MHz is designed.The choke sleeve is mainly used to choke the strong current at the edge of the cavity of the back cavity base station antenna.Using the two-element antenna and four-element two-column antenna array composed of the antenna element,their own matching and polarization isolation are almost the same as the element,while the same polarization isolation between element and columns has been greatly improved,and the isolation between different polarizations has also been improved to a certain extent.At the same time,the degree of distortion of the radiation pattern is very small,and the axial gain and half-Power Beam width are very stable.