Research On Wideband MIMO Antennas With High Isolation

With the fast development of wireless communication technology,the demand of electronic terminals for spectrum resources is growing,and the demand of communication system for high-quality and large capacity data transmission is becoming more and more urgent.MIMO technology can use multi-path transmission to overcome channel fading and exponentially increase channel capacity without increasing transmission power and spectrum.As the core device of MIMO communication system,MIMO antenna has become a research hotspot in the current academic field.In addition,the trend of miniaturization of terminal equipment intensifies the coupling effect between antenna elements in a narrow space.In this paper,the design of wideband MIMO antennas and decoupled structures are studied,the main innovations are as follows:Point 1:the bandwidth and isolation of MIMO antenna are improved by using ground branches and parasitic open ring structure.MIMO antenna is composed of two planar monopoles.Its bandwidth and isolation are increased by introducing the stub on the ground.Then,a split-ring structure is loaded around the monopole radiator.The bandwidth is expanded by 2.55 GHz without increasing the overall size of the antenna.Finally,the antenna covers 3.1-5.65 GHz frequency band,and achieves isolation of more than 15 dB.The overall radiation performance of the antenna is good.Point 2:the polarization diversity and slot structure are used to reduce the coupling effect between MIMO antenna elements.The antenna element adopts the slot and stub structure to achieve the broadband performance.MIMO antenna consists of four antenna elements by polarization diversity technology.In order to further reduce the coupling,the slot structure is loaded between adjacent elements.The slot effectively restrains the effect of mutual coupling.Both the impedance matching and isolation characteristics are improved.The measured results show that the isolation of the MIMO antenna is greater than 17.5 dB in the frequency range of 2.31-7.95 GHz.Point 3:the isolation of MIMO antenna is improved by the combination of two defected ground structures.The antenna element is designed based on the open slot structure.It shows the ultra-wideband characteristic by improving the structure.MIMO antenna consists of two symmetrical antenna elements.A decoupling network based on two defected ground structure is loaded between the elements.The structure limits the flow of coupling currents and does not deteriorate the impedance matching performance of the antenna.The test results show that the MIMO antenna can cover the UWB band and the isolation is more than 20 dB.In addition,the diversity performance of the antenna is also discussed.The envelope correlation coefficient,average effective gain and diversity gain all meet the design requirements.