Recent Advancements in User Effect Mitigation for Mobile Terminal Antennas: A Review

A dramatic evolution can be observed in cellular wireless communication. It started from analog 2G (global system for mobile communication) toward high-data-rate systems such as 3G (wideband code-division multiplexing access), 3.5G (high-speed packet access), 4G (long-term evolution (LTE) and LTE advanced), and currently converging in a more optimized and compact 5G (orthogonal frequency-division multiple access) form. The main challenges for designing of mobile terminal antennas are the compact size requirement of the built-in structure, multiband capabilities, and the number of integrated antennas that form a multiple-input multiple-output (MIMO) terminal system. Moreover, they are required to fulfill all performance and safety standards. For mobile antennas, their radiation efficiency may be affected by the interaction of user head/hand, which consequently affects the correlation of MIMO antenna systems. This paper provides an overview of user effect on mobile terminal antennas in the last seven years. An overview of the Cellular Telecommunication and Internet Association specifications for mobile terminal antennas will first be explained. This is followed by a discussion on the user's effects on MIMO parameters, channel capacity on mobile terminal antennas, and millimeter-wave applications prior to the presentation of recent technologies that are aimed at improving the antenna performance. Finally, a perspective and potential future investigations on mobile terminal antennas will be discussed in the conclusion.