A communication device includes a system ground plane, a ground element, an antenna element, and a metal guide line. The ground element is coupled to the system ground plane. The ground element has a first edge, a second edge, and a connection point. The first edge and the second edge are opposite to each other. The connection point is positioned at the second edge. The antenna element is disposed adjacent to, or at, the first edge. One end of the metal guide line is coupled to the connection point, and another end of the metal guide line is open.