An antenna structure includes a dipole antenna element, a closed-loop conductor, and a reflection plane. The dipole antenna element is configured to transmit an electromagnetic signal. The closed-loop conductor is disposed adjacent to the dipole antenna element. The dipole antenna element is substantially between the closed-loop conductor and the reflection plane, or the closed-loop conductor is substantially between the dipole antenna element and the reflection plane. The reflection plane is configured to reflect the electromagnetic signal from the dipole antenna element so as to enhance the total gain of the antenna structure. The mutual coupling effect between the closed-loop conductor and the dipole antenna element effectively causes the distance between the dipole antenna element and the reflection plane to be shorter.