Mutual Coupling Control Technology In Multi-antenna System

With the development of technology,wireless communication system has been developing rapidly.As a key technology in the fifth generation(5G)wireless communication system,multiple input multiple output(MIMO)technology aims to improve the channel capacity and ensure the reliability of data transmission by using multiple antennas in the transceiver of communication system.Compared with previous generations of communication systems,the number of antennas in 5G system has increased several times or even dozens of times.However,whether in the base station system or the terminal system,the space occupied by the antenna is limited,so the overall layout of the antenna will be very compact.The increasing number of antennas and limited space will inevitably lead to strong mutual coupling between antennas,which will affect the performance of the whole communication system.Therefore,it is necessary to study the coupling suppression in multiantenna system.Based on this,the corresponding decoupling methods and structures are proposed and designed to reduce mutual coupling and improve the performance of antennas in this dissertation.The focus of this content can be summarized in the following three aspects:1.The coupling suppression method based on parasitic structure is studied.For singleand dual-band multi-antenna elements,different parasitic structures are designed to suppress mutual coupling.Firstly,in order to suppress the mutual coupling in a relativly small space,a compact resonator structure is proposed to suppress the surface wave in the microstrip patch multi-antenna system,so as to improve the isolation performance between the antenna elements.The proposed resonator structure can not only improve the isolation of microstrip patch antennas coupled in H-plane,but also be suitable for ones coupled in E-plane.The results show that the resonator structure can achieve high isolation performance in a small spacing.Secondly,applying the designed coupled resonator structure to more antennas can also improve the isolation between each antenna unit.Finally,for the dual-band Wi-Fi multiantenna system,in order not to increase the complexity of the system,a single parasitic structure is designed to achieve the coupling suppression between the two dual-band antennas.By loading open circuit impedance at the end of the designed dual-band parasitic structure and using Y-matrix analysis,the isolation improvement of dual-band antenna in two operating bands of 2.45 GHz and 5.8 GHz can be achieved simultaneously.Moreover,the prototype processing and performance test of the antenna further show the reliability and correctness of the proposed parasitic structure.2.The coupling suppression method based on ceramic superstrate is studied.In order not to occupy more space between antenna elements and increase the complexity of feed back end,a multi-antenna coupling suppression design based on ceramic superstrate is proposed.The ceramic superstrte with high permittivity is used to improve the the isolation characteristics between antenna elements.By loading a ceramic superstrate over antennas,the near-field coupling distribution between antenna elements can be changed,and the coupling field distribution on the coupling elements can be eliminated,so as to improve the isolation characteristics.In the mono-polarized multi-antenna system,the isolation between two dipole antennas coupled in H-plane with a spacing less than 0.3λ can be improved by15-30 d B.Moreover,in order to improve the deterioration of cross-polarization caused by the introduction of ceramic superstrate,the method of grooving in the ceramic superstrate is adopted to ensure the stability of radiation characteristics.Furthermore,on the basis of monopolarization decoupling,the dual-polarized antenna decoupling design based on ceramic superstrate is studied.Similar to monopolarization,using ceramic superstrate with high permittivity,the isolation between the ports of antenna elements can be improved to more than 25 d B when the element spacing is 0.4λ.The prototype of the mono-polarized antenna is fabricated and tested.The results show that the decoupling design is accurate.3.The coupling suppression method based on metasurface superstrate is studied.Combined with the decoupling design of ceramic superstrate,different types of metasurface structures are proposed by using the method of equivalent electromagnetic parameters extraction.By loading different types of metasurface superstrate,the decoupling designs of different multi-antenna are realized respectively.In the single-band multi-antenna decoupling design,the isolation between antennas can be improved to more than 25 d B when the spacing between antenna element is less than 0.3λ.Moreover,due to the polarization characteristics of the metasurface,the radiation characteristics of the antenna will not be deteriorated.Furthermore,on this basis,a dual-band decoupling structure is designed to suppress the coupling between compact dual-band multi-antenna.The metasurface composed of non-uniform cut wires with different lengths can improve the isolation of two working bands of dual-band antennas simultaneously.In the 2.6 GHz and 3.5 GHz operating band,the isolation between antenna elements can be increased by 24 d B and 15 d B respectively.Finally,for the decoupling design of dual-polarized multi-antenna,according to the polarization form of the antenna,a metasurface structure with square metal sheets periodically arranged is adopted to improve the isolation performance between the antenna ports and ensure the stability of antenna radiation performance.In the 3.4-3.6 GHz frequency band,the isolation between each port of the antenna can be improved to 25 d B under the premise of good matching,especially the isolation between the same polarized antennas can be improved to more than 30 d B.Meanwhile,prototype processing and testing of the abovementioned antennas are carried out,and the measured results further demonstrate the reliability of the metasurface decoupling design.