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%.