  A compact multiple-input-multiple-output (MIMO) antenna with very high
isolation is proposed for ultrawide-band (UWB) applications. The antenna with a
compact size of 30.1x20.5 mm^2 (0.31${\lambda}_0$ x0.21${\lambda}_0$ ) consists
of two planar-monopole antenna elements. It is found that isolation of more
than 25 dB can be achieved between two parallel monopole antenna elements. For
the low-frequency isolation, an efficient technique of bending the feed-line
and applying a new protruded ground is introduced. To increase isolation, a
design based on suppressing surface wave, near-field, and far-field coupling is
applied. The simulation and measurement results of the proposed antenna with
the good agreement are presented and show a bandwidth with S 11 < -10 dB, S 12
< -25 dB ranged from 3.1 to 10.6 GHz making the proposed antenna a good
candidate for UWB MIMO systems.
