A communication device (1, 4, 5), comprising: a ground element; a dielectric substrate, disposed nearby the ground element, the dielectric substrate having a first surface and a second surface; and an antenna element, comprising a first metal portion and a second metal portion (14, 44), wherein the antenna element and the ground element form a ground plane antenna, the first metal portion is disposed on the first surface and has a feeding point located on the first surface, the ground plane antenna is operated in a frequency band through the first metal portion, the second metal portion (14, 44) is disposed on the second surface to improve the impedance matching of the ground plane antenna in the frequency band, the first metal portion is electrically connected to the second metal portion (14, 44) through a conductive via-hole (15, 551, 552), wherein the first metal portion comprises a first edge away from the ground element and a second edge nearby the ground element, a first end of a diagonal of the first metal portion is connected to an end of the first edge, a second end of the diagonal of the first metal portion is connected to an end of the second edge, the conductive via-hole (15, 551) is nearby the first end of the diagonal of the first metal portion, the feeding point is nearby the second end of the diagonal of the first metal portion, and a projection of the second metal portion (14, 44) on the first surface is covered by the first metal portion characterised in that a shape of the first metal portion is an inverted U shape and the first edge is an edge of a middle section of the inverted U shape. a ground element; a dielectric substrate, disposed nearby the ground element, the dielectric substrate having a first surface and a second surface; and an antenna element, comprising a first metal portion and a second metal portion (14, 44), wherein the antenna element and the ground element form a ground plane antenna, the first metal portion is disposed on the first surface and has a feeding point located on the first surface, the ground plane antenna is operated in a frequency band through the first metal portion, the second metal portion (14, 44) is disposed on the second surface to improve the impedance matching of the ground plane antenna in the frequency band, the first metal portion is electrically connected to the second metal portion (14, 44) through a conductive via-hole (15, 551, 552), wherein the first metal portion comprises a first edge away from the ground element and a second edge nearby the ground element, a first end of a diagonal of the first metal portion is connected to an end of the first edge, a second end of the diagonal of the first metal portion is connected to an end of the second edge, the conductive via-hole (15, 551) is nearby the first end of the diagonal of the first metal portion, the feeding point is nearby the second end of the diagonal of the first metal portion, and a projection of the second metal portion (14, 44) on the first surface is covered by the first metal portion characterised in that a shape of the first metal portion is an inverted U shape and the first edge is an edge of a middle section of the inverted U shape.