On user effects in MIMO handset antennas designed using characteristic modes

The Theory of Characteristic Modes (TCM) has been applied to design high-performance MIMO antennas for mobile terminals. However, existing studies focus on free-space (FS) performance, which is mostly irrelevant in real usage. This paper investigates the performances of two TCM-based MIMO terminal antenna designs in 7 realistic user scenarios for frequencies below 1 GHz. Full-wave simulation results indicate that the TCM designs can significantly outperform conventional designs in user scenarios that require good MIMO performance. Higher multiplexing efficiency (ME), by up to 3 dB, was recorded for a TCM design relative to a conventional terminal in a two-hand scenario. Performance advantages of the TCM designs were mainly due to lower correlation as well as higher impedance matching and coupling efficiency. Moreover, a combined usage study based on weighted ME over different user cases established that on average TCM designs outperform conventional designs by up to 1.6 dB. This suggests that the TCM designs not only give superior performance in FS, but also in realistic user scenarios.