An ultra-wideband shorted dipole antenna includes a coaxial cable line and first and second open-loop radiating metal plates with substantially the same shape. The coaxial cable line has a central conducting wire and an outer grounder sheath. The first and second open-loop radiating metal plates are symmetrically disposed on two sides of the antenna to form two arms of the antenna and are electrically connected to each other. Each of the first and second open-loop radiating metal plates has a signal feeding point electrically connected to the central conducting wire or the outer grounder sheath of the coaxial cable line.