An antenna assembly includes a carrier, a metal sheet, and an antenna. The metal sheet is attached to the carrier and defining at least one notch. The antenna is connected to the metal sheet and includes a radio body for receiving and transmitting wireless signals. The radio body is positioned above the metal sheet. The length of current path in a peripheral wall of the at least one notch is in a predetermined proportion to the wavelength of the wireless signals, enabling the metal sheet to resonate with the radio body to increase the bandwidth of the antenna.