A double-printed u-shape antenna for ultra-band application is proposed in this paper. With two U-shape dipole arms printed on the dielectric substrate and fed by a microstrip line, the antenna realized it's ultra-wideband character by multistage impedance conversion. The impedance characteristic, radiation patterns and the transfer function are studied both by numerical simulation and experiment. The radiation patterns are approximately omni-directional with the VSWR < 2 from 3.08 to 11.57 GHz. Both transfer functions and group delay are smooth with linear phase which is valuable for the transmission of UWB signals.