Research And Design Of MIMO Antenna For LTE Band

Multiple-input-multiple-output（MIMO）technology is a major breakthrough in smart antenna technology in the wireless communication field.It has the advantages of increasing channel capacity and reducing multipath fading,especially in Long Term Evolution（LTE）applications（1.7-2.7 GHz）,which can be used to improve data transmission rate without increasing bandwidth or transmit power.However,when multiple antennas are placed in a communication device with a limited volume,due to the increase of antennas and the decrease in the distance between the antenna units,strong coupling between the antenna units will occur.At the same time,it will also affect the performance of the antenna’s impedance matching and radiation pattern.Therefore,improving the isolation between antenna elements is a core issue in the design of a multi-antenna system.In this thesis,the research and design of decoupling technology of MIMO antenna for LTE band are carried out.The details are as follows:1)A planar MIMO antenna is designed with high isolation for LTE band.The designed MIMO antenna is composed of two symmetrical radiating elements,and the radiating element adopts a“C”shaped split ring structure.Through the electromagnetic coupling between the two“C”shaped split rings on the front and back of the substrate,two close resonant frequencies are generated respectively,and the wide frequency band of LTE is realized.A T-slot is introduced on the ground plate on the back of the dielectric substrate to reduce the coupling of higher frequency band in the working frequency band,and a resonant branch is inserted in the T-slot on the back of the substrate to reduce the coupling of lower frequency band in the working frequency band.The isolation between the two ports of the antenna reaches more than 18 d B,and decoupling structure effectively reduces the mutual coupling between the MIMO antennas.2)A vehicular MIMO antenna is designed with high isolation for LTE band.The designed MIMO antenna is composed of two inverted-F antennas,which are installed vertically on a horizontal ground plane.The inverted-F antenna consists of a tapered step impedance patch and a grounded strip.By introducing a fractal decoupling structure composed of four fractal unit slots and a line slot between the two inverted-F antennas,multiple current paths are generated,thereby increasing the decoupling bandwidth.When the antenna has a close separation distance of 0.18λ₀（λ₀ is the free-space wavelength at the center frequency of 2.2 GHz）,the designed fractal decoupling structure can obtain good isolation in the broadband MIMO antenna,and the isolation is improved by 8.3-38 d B.