Research And Design Of MIMO Antenna

With the society development,people put forward higher requirements for communication quality.However,the scarcity of spectrum resources and the multi-path fading of wireless channel seriously affect the development of wireless communication technology.Multiple Input Multiple Output(MIMO)technology can establish multiple parallel transmission channels between transceiver and receiver systems,which greatly increase the channel capacity and spectrum efficiency.In MIMO system,channel isolation is a very important index,and the channel isolation is greatly affected by the isolation between antenna elements.When the antenna elements spacing is small,it will lead to poor isolation.However,due to the demand of miniaturization of mobile terminals,there is less and less space left for the antenna,so how to ensure the isolation of the MIMO antenna in a compact space becomes an important problem to be solved.This paper focuses on the design of MIMO antenna for mobile terminals and the decouple method.1.A dual-frequency 5G four-element MIMO antenna for mobile terminal is designed,with operating bands of 2.5-2.7Ghz and 3.4-3.6Ghz.The four antenna elements are located at the upper and lower ends of the mobile terminal.Due to the close distance between the two elements,the isolation between them is poor.In order to improve isolation,we innovatively placed the port of a element in the protruding position of the floor.The isolation is improved in two bands simultaneously.The MIMO antenna reflection coefficient in 2.5-2.7Ghz and 3.4-3.6GHz bands is less than-10 d B,the isolation in 2.5-2.7Ghz band is increased by 1d B,which is 12.5d B,and the isolation in 3.4-3.6GHz band is increased by 3.5d B,which is 17.5d B.The antenna radiation efficiency is greater than 50%.2.A mobile terminal antenna element(3.4-3.6GHz)with a natural decoupling structure is designed,which ensures excellent isolation between ports when the distance between two ports is very small without adding any additional decoupling structures.When the distance between two ports is only 1.2 mm(0.014l,wavelength at 3.5 GHz),the isolation between two ports is greater than 12.5d B,up to 28 d B.Six antenna elements are placed on the long border on both sides of the mobile terminal to form the MIMO antenna with 12 ports.Finally,the 12-port MIMO antenna reflection coefficient less than-10 d B,transmission coefficient less than-12 d B,efficiency greater than 84%,ECC less than 0.02?3.Innovative improvements have been made to the traditional parasitic element decoupling method.When the MIMO antenna is decoupled by the traditional decoupling method,the impedance matching of the antenna is often deteriorated.In order to match the antenna,matching circuits need to be added.MIMO antennas can be matched and decoupled simultaneously by the improved method,no need to add matching circuits,simplifying antennas design and facilitating the miniaturization of antennas.Two MIMO antennas are designed as examples to prove the method.One is a ground radiation antenna(Gradi Ant)and the other is a MIMO monopole antenna.Finally,the isolation of the two MIMO antennas is greatly improved by using this method,and impedance matching can be completed in the operating frequency band without adding matching circuit.