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In recent years, the screen-to-body ratio of
mobile handsets has been increasing. Today, the screen nearly fills up the
entire front side. Conventionally, the screen is mainly seen as a metallic
object that adversely affects antenna performance. In this paper, the large
screen is used for the first time to facilitate an additional uncorrelated MIMO
port in a tri-port design, for several LTE bands below 1 GHz. To this end, the
design procedure explicitly considers the screen together with the terminal
chassis, which can be simply modelled as two metal plates. In particular,
characteristic mode analysis of the double-plate model enables a sufficient
number of resonant modes to be created, tuned and selectively excited to yield three
uncorrelated MIMO ports in the low band. Simulation and measurement results are
found to be in good agreement. The measured bandwidths of the three ports are
23%, 17% and 21%, respectively. Within the operating band, the measured
isolation is above 13 dB, envelope correlation coefficient below 0.16 and average
total efficiency above 72%.