Abstract: A communication device including a ground plane and an antenna system is provided. The antenna system includes at least two antennas, which are both located at a first edge of the ground plane and operate in at least a first band. The ground plane has at least one slit, and an open end of the slit is located at a second edge adjacent to the first edge. The open end of the slit has a distance of at least 0.2 wavelength of a frequency in the first band to the first edge. When the antenna system operates in the first band, the slit can attract excited surface currents on the ground plane, thereby causing weaker surface currents flowing along the first edge of the ground plane. The coupling between the at least two antennas in the antenna system is hence decreased.

Abstract: An antenna structure having a ground element and an antenna element is provided. The antenna element is disposed on a dielectric substrate, and includes a first radiation portion, a second radiation portion, and a spiral metal line. An end of the first radiation portion is a feeding point of the antenna element, and another end is open. An end of the second radiation portion is electrically coupled to the ground element, and the length of the second radiation portion is greater than that of the first radiation portion. The first radiation portion is surrounded by the second radiation portion. An end of the spiral metal line is coupled to the first radiation portion. The spiral metal line contributes a parallel resonance outside the antenna's operating band, and results in a resonant mode generated within the antenna element's operating band such that the operating bandwidth of the antenna element is increased.