A two-port planar ultra-wideband (UWB) pattern diversity antenna is proposed in this letter. The design consists of an array of two rotated identical monopole antennas and two feeding ports with 0° in-phase and 180° out-of-phase excitations. The single monopole antenna includes a circular patch, a rectangular truncated ground plane and a fork-shaped feeding structure. In this antenna, a modified partial common ground plane is used to enhance the input matching, increase the isolation between antenna elements and improve the desired radiations. The measured results show an |S₁₁| < −10 dB bandwidth ranging from 2 to over 20GHz, with conical and broadside beams, high efficiency, and good isolation across the entire UWB band. Also, the proposed antenna exhibits a smaller footprint, larger bandwidth, and more straightforward design compared with the existing designs. To the best of authors’ knowledge, all these characteristics have never been presented in previously reported UWB pattern diversity antennas.