An antenna system includes a first dipole antenna element and a second dipole antenna element. The first dipole antenna element includes a first feeding radiation element and a first grounding radiation element. The first feeding radiation element has an extension portion. The first grounding radiation element has an open slot. The extension portion extends into the interior of the open slot. The second dipole antenna element includes a second feeding radiation element and a second grounding radiation element. The first dipole antenna element and the second dipole antenna element are both excited by a signal source. The first dipole antenna element operates in a low-frequency band. The second dipole antenna element operates in a high-frequency band.