A small ultra wideband (UWB) antenna designed to have a unidirectional radiation pattern is disclosed. The UWB antenna includes a substrate; a power feeding part, provided on an upper surface of the substrate, for receiving a supply of an external electromagnetic energy; a dipole radiator excited by the electromagnetic energy fed through the power feeding part and radiating electromagnetic waves in one and the other directions of the substrate; and an active loop radiator excited by the electromagnetic energy fed through the power feeding part, respectively enhancing and canceling the electromagnetic fields produced in one or the other directions of the substrate by the dipole radiator.