Multiple Inputs and Multiple Outputs (MIMO) antennas are required for mobile phones in 5G and beyond. One of the biggest challenges is: How to achieve high isolation between antennas closely packed? This talk gives a brief overview of various techniques proposed in recent years, such as the use of parasitic elements, neutral lines, metamaterials, electromagnetic band gap (EBG), etc. It is shown that these techniques could achieve good isolation up to about 20 dB when antenna elements have a distance of about half wavelength, but the performance deteriorates quickly when the antenna elements distance is reduced further. A technique called Common-Mode/Differential-Mode (CM/DM) antenna design is then presented. The CM/DM technique is shown to be able to achieve high isolation over 20 dB when the antenna elements have zero distance between them. The technique is promising for achieve compact-size highly integrated MIMO antenna systems for smart phones in 5G and beyond.
Steven Gao is a Full Professor and Chair in RF and Microwave Engineering, and the Director of Graduate Studies at the School of Engineering and Digital Arts, University of Kent, UK. His research covers smart antennas, phased arrays, MIMO, reconfigurable antennas, wideband/multiband antennas, antennas for mobile communications/satellite communications/IOT, RF/microwave/mm-wave/THz circuits, UWB radars, synthetic-aperture radars, and sensors for healthcare. He co-authored/co-edited three books (Space Antenna Handbook, Wiley, 2012; Circularly Polarized Antennas, IEEE-Wiley, 2014; Low-Cost Smart Antennas, Wiley, 2019), over 300 papers and 10 patents. He is an Associate Editor of IEEE Transactions on Antennas and Propagation and several other international Journals (Radio Science, IEEE Access, Electronics Letters, IET Circuits, Devices and Systems, etc), and the Editor-in-Chief for John Wiley & Sons Book Series on “Microwave and Wireless Technologies”. He was a Distinguished Lecturer of IEEE Antennas and Propagation Society (2014-2016), and General Chair of LAPC 2013, UK. He was an Invited Speaker at many conferences. He was named a Fellow of IEEE due to his contributions to reconfigurable antennas and broadband printed antennas. He is also a Fellow of Royal Aeronautical Society, UK, and a Fellow of IET.