User effect on the MIMO performance of a dual antenna LTE handset

Abstract

This study focuses on the user influence on a MIMO antenna system in a smart phone form factor. The antenna system is designed to have a low coupling and correlation between its two antennas. The study is based on time-domain simulations of the antenna system in free space and with a head and hand phantom using a commercially available Finite Element Method solver. The MIMO parameters are evaluated with three different channel models. A static grip only gives one case of the user effect so the hand phantom is modified with a moving finger that is swept across the backplane of the phone. Based on the results of the study it is concluded that the placement of the index finger has a significant effect on the simulated antenna system. For certain finger placements the mismatch loss and absorption loss both change more than 5 dB. Overall the antenna system shows good MIMO performance in free space but suffers under the influence of the user. Especially the diversity antenna is heavily detuned and gives a total efficiency of −19.1 dB worst case compared to −1.9 dB in free space. The branch power ratio is increased by the user while the envelope correlation is decreased by the user.