Current Misuses and Future Prospects for Printed Multiple-Input, Multiple-Output Antenna Systems

In the past six years or so, the number of scientific articles and conference papers providing possible multiple-input, multiple-output (MIMO) antenna system solutions has noticeably increased. Flagship conferences on antennas and propagation have recently had multiple sessions addressing MIMO antenna systems and their applications. The importance of such antenna systems lies in the magnitude of their application in current wireless devices and gadgets, and this thrust will continue because fourth-generation (4G) and the upcoming fifth-generation (5G) wireless standards rely heavily on MIMO technology. But throughout the years, and up until now, a wide range of publications still suffer from some major misconceptions and unclear understanding of the fundamental aspects while designing, characterizing, and evaluating such multi-antenna systems. In this article, I shine some light on a few of these fundamental issues and try to clarify them. Some examples from the literature are given to show the magnitude of such issues, and the goal is to try to avoid them in all future works. Finally, some prospects for the use of MIMO-based antenna systems in upcoming wireless standards and their enabling technologies are presented.