A compact planar ultra-wideband (UWB) antenna for multiple-input-multiple-output /diversity applications is proposed in this study. The proposed antenna consists of three staircase-shaped radiating elements, and is fabricated on a single 45 mm × 25 mm substrate of dielectric constant 4.3 and thickness 1.588 mm. It offers a 2:1 voltage standing wave ratio impedance matching in the entire UWB band, as specified by the Federal Communications Commission. Spatial, polarisation and pattern diversities within the antenna elements ensure an average isolation of 25 dB throughout the operating band. Moreover, the antennas have directional radiation patterns with stable gain and favourable radiation efficiencies. Good pattern diversity with better transient responses, low envelope correlation coefficient and ample mean effective gain within the UWB band, are the attractive features of this antenna.