MIMO systems and antennas for terminals

MIMO technology has facilitated tremendous performance improvements in wireless communications, allowing the data rate to increase linearly with the number of antennas used, at no additional expense in transmit power or spectrum. However, the tremendous performance gain can only be achieved by multi-antenna designs that provide low coupling and correlation, as well as high total efficiency. Such design criteria are especially challenging for small terminal devices. The situation becomes even more complicated with increasing bandwidth requirements for terminals in existing and upcoming mobile communication standards. Beginning with the history of MIMO terminal antenna and its evaluation methods, this chapter is geared towards providing useful guidelines to researchers and practitioners alike on how to design efficient MIMO antennas for terminals. The focus is on decoupling and decorrelation techniques, including RF circuit level decoupling, antenna structure decoupling and characteristic mode based decoupling. Future directions in MIMO antenna design and some corresponding open problems are also described.