A directional ultra-wideband(UWB)antenna with improved radiation patterns is presented.The proposed sheme comprises a differential-fed microstrip antenna and a rectangular cavity.The hexagon-shaped slot and four triangle-cut corners on the ground plane of the planar antenna are used to improve the impedance matching within the UWB frequency range.A rectangular cavity is used as the reflector for the planar microstrip antenna,so as to achieve directed radiation.The measured results indicate that the designed antenna exhibits a stable broadside directional radiation patterns within the entire operating frequency band.Furthermore,thanks to the differentially driven technique,the cross-polarization is greatly decreased and the polarization purity is maintained in a high level. A directional ultra-wideband (UWB) antenna with improved radiation patterns is presented. The proposed sheme comprises a differential-fed microstrip antenna and a rectangular cavity.The hexagon-shaped slot and four triangle-cut corners on the ground plane of the planar antenna are used to improve the impedance matching within the UWB frequency range. A rectangular cavity is used as the reflector for the planar microstrip antenna, so as to achieve directed radiation. The measured results indicate that the designed antenna exhibits a stable broadside directional radiation patterns within the entire operating frequency band. Hotter, thanks to the differentially driven technique, the cross-polarization is greatly decreased and the polarization purity is maintained in a high level.