Design approaches for electrically small MIMO antenna systems on mobile devices

An overview of design goals and approaches to the design of MIMO antennas for mobile terminals is presented. Figures of Merit (FOMs) for multiport antennas are derived based on consideration of transmit mode and receive mode for the Downlink - Transmit Diversity scheme and the Closed-loop Spatial Multiplexing (CL-SM) scheme of LTE. Total multiport efficiency and imbalance figure are identified as the most relevant FOMs. A systematic design approach by which the radiation modes of a multiport antenna are derived from the characteristic modes of the device´s chassis are presented. Some aspects of this approach are illustrated by example.