Research On Miniaturized Multiband/ Broadband MIMO Antenna Decoupling Technology

In recent years,with the rapid development of wireless communication technology,the demands for high data rate and large channel capacity are increasing.As we know,multiple input multiple output(MIMO)technology can use the multipath effect to greatly improve the channel capacity and spectral efficiency without increasing the input power.Theoretically,the more ports in MIMO system,the larger channel capacity can be obtained.However,more antenna elements and less spacing will lead to a stronger coupling,consequently decreasing the performance of MIMO system.Therefore,how to reduce the mutual coupling is a key problem in the miniaturized MIMO antenna design.Another method to improve spectrum efficiency is the co-frequency co-time full duplex(CCFD)wireless communication technology.CCFD wireless communication allows simultaneous transmission and reception of signals within the same bandwidth,which greatly increases the spectrum utilization and channel capacity in theory.Nevertheless,in the implementation of CCFD,the large power difference between the strong self-interference and the weak received signal is a great challenge for the designers.Therefore,the self-interference problem between local transmitter and receiver must be first solved to realize CCFD communication.In this dissertation,on the one hand,based on the miniaturized MIMO wireless communication system,the design of single band,multiband and broadband MIMO antenna is put forward respectively,with emphasis on the methods to improve the isolation between antenna elements.On the other hand,based on the CCFD wireless communication system,the design of transceiver antenna is proposed,and the corresponding method to decrease the self-interference between local antennas is studied.The main work and innovation are summarized as follows:1.In order to solve the coupling problem of MIMO antenna working in single band,a single band decoupling method of 2×2 MIMO is proposed.And a miniaturized MIMO antenna with high isolation characteristic working in the 2.4GHz band is designed.The antenna consists of two symmetrically arranged folded monopole antenna elements,and the distance between the elements is 0.1₀(₀ represents the free space wavelength at 2.4GHz).Based on the superposition principle of the electromagnetic field,a printed planar spiral decoupling structure is designed between the elements to reduce the coupling current.The measured results show that after adding the decoupling structure,the MIMO antenna achieves good design parameters and isolation characteristics in the operating frequency band.Therefore,it is suitable for wireless local area networks(WLAN)and other wireless communication systems.2.In order to solve the coupling problem of MIMO antenna working in multiband,a multiband decoupling method of 2×2 MIMO is further proposed.And a dual band miniaturized MIMO antenna with a high decoupling effect working in 2.4GHz and 5GHz frequency bands is designed.The antenna achieves dual band operation by adding a new open-circuit stub to the folded monopole antenna.The decoupling structure is located between the antenna elements,and is composed of a planar spiral resonance structure(low band decoupling structure)and an inverted L-shaped structure(high band decoupling structure).The actual measurement shows that after adding the decoupling structure,the antenna achieves good design parameters and port isolation in the operating frequency band,and can cover multiple operating frequency bands such as 2.4/5.2/5.8GHz WLAN.In addition,the decoupling structure and the design of the antenna element are independent of each other,so it can be used in the high isolation design of other form printed MIMO antennas.3.In order to solve the coupling problem of broadband MIMO antenna,a wideband decoupling method is presented,which combines the dual polarization characteristic with a decoupling structure.And a broadband cross-polarized MIMO antenna with a high isolation is designed.The antenna consists of two patch dipole antenna elements placed orthogonally.In order to increase the bandwidth,the square radiation patch of the dipole is chamfered,and a rectangular parasitic patch placed vertically is added.And in order to suppress the surface current and improve the port isolation,a decoupling unit composed of a planar spiral resonance structure and an inverted L-shaped structure is introduced between the two antenna elements.The measured results show that after adding the decoupling structure,the working bandwidth of the cross-polarized MIMO antenna reaches 62%(VSWR<1.5),and the average port isolation is greater than 30d B,which covers several different frequency bands in the mobile communication system and can be applied to the base station.4.In order to solve the self-interference problem of CCFD wireless communication system,a coupling suppression method of local antennas is put forward.And a collinear dipole antenna pair with high isolation characteristic is designed.By placing two dipoles1.43₀(₀ represents the free-space wavelength at 2.45GHz)apart to each other's zero-radiation direction and combining the proposed self-interference suppression structure,the port isolation of them reaches more than 50d B on a relative bandwidth of 14.8%.Moreover,the addition of the self-interference suppression structure has little effect on the original characteristic parameters of the transmitting and receiving antenna.For other antenna types,it can be placed in a plane perpendicular to the magnetic field to achieve high transmitter-receiver isolation.This structure can be combined with analog and digital suppression methods to reduce the total self-interference to an acceptable level.