The Research On Coupling Control Technologies Of Antennas

With the rapid development of modern mobile wireless communication,the explosive growth of wireless communication and broadband data services,is currently moving to the 5G mobile communication system.Channel capacity puts forward higher requirements.At present,MIMO acting as a method to improve the channel capacity,becomes an indispensable part for future communication system.Antenna arrays consists of hundreds of antenna elements,which are generally placed in limited space.It is necessary to study the suppression of electromagnetic coupling.In addition,it is necessary to install many narrowband antennas on the same device.As an alternative scheme to improve the channel capacity of the system,the study on broadband antennas is highly demanded.The topics and difficult problems are studied in this dissertation based on some scientific research projects.Two kinds of methods to solve the channel capacity for antenna system are discussed respectively,such as using MIMO technology or broadening system bandwidth based on the control problems of electromagnetic coupling.The research achievements can be summarized as the following three parts.1.Based upon the electromagnetic coupling control technology,the performance of the branches on the suppression of the mutual coupling is studied.Also,the high-isolation technique based on the decoupling branches as well as the reasons and computing methods for mutual coupling in antenna array is analyzed.a)By analyzing the deformation of the monopole array,the high isolation in some specific frequencies can be achieved by utilizing a single connection line.Then an impedance matching circuit is designed for the antenna by using Keysight ADS.Combined the two design stages mentioned above,a MIMO antenna with high first-order isolation is finally obtained.b)In the design,a cross-finger coupling line is utilized to replace the simple connection line and an open ring is properly introduced for suppressing the mutual coupling of the antenna.The influence of the cross-finger coupling line and the open ring on the port isolation is analyzed.Then a second-order high-isolation MIMO antenna is realized,without additional matching circuit.2.Based upon the electromagnetic coupling control technology,the performance of the metasurface on the coupling suppression is studied.Its application background and extraction methods for important parameters are briefly introduced.a)First,the negative permeability properties of the designed metasurface is calculated by analyzing the property of the resonant ring.Then the effect of the metasurface on the transmission of the electromagnetic wave is analyzed by comparing the port isolation of the MIMO antenna with and without the metasurface.After detailed theoretical analysis,the designed antenna is fabricated and measured in order to verify the effectiveness of the MAAD technology in decoupling the antenna array.By changing the number of resonant units,such as 6×4,7×5,8×6,the influence of the metasurface size on the port isolation is studied.In order to further verify the feasibility of this metasurface technique on Massive MIMO,it is applied in the 1×4 and 1×8 arrays and the performance of the metasurface on the coupling suppression is studied.b)Another technique to improve the port isolation is to install EBG,DGS or other structures between two antennas.Since the space between antennas is generally limited,some periodic units surrounding the antennas are designed to change the current path,which can improve the isolation.3.Based upon the electromagnetic coupling control technology,some wideband antennas are researched.Broadening the band of operation of antennas are another method to improve the channel capacity of wireless communication systems.a)By improving the original structure and using the electromagnetic coupling between the feeder and the main radiator,a second-order broadband UHF antenna used for RFID is designed.Its working mechanism is deduced in detail,which provides the idea for designing broadband antennas.Based on the antenna designed in a),a short probe is introduced to improve the input impedance of the antenna,thus obtaining another broadband antenna for RFID application.c)Since there are some frequency bands used for other wireless communication systems,the crossover between the UWB band and other narrow frequency bands.Based on electromagnetic coupling technology,by adjusting the mutual coupling between the mushroom structures and the feeder as well as the mutual coupling between parasitic branches and the main radiator,an UWB antenna with three narrow rejection bands is realized.Some key parameters affecting the three rejection bands are analyzed.It should be pointed out that the second rejection band achieves perfect square notch,which is one contribution of this design.