An antenna system includes a first transformer, a first transceiver, a first switch, a second switch and an antenna. The first transformer includes a primary winding, and a secondary winding. The primary winding includes a first terminal and a second terminal, and the secondary winding includes a first terminal and a second terminal. The first transceiver is coupled to the first terminal of the primary winding of the first transformer. The first switch is coupled between the first terminal of the secondary winding of the first transformer and a ground. The second switch is coupled between the second terminal of the secondary winding of the first transformer and the ground. The antenna is coupled to the first terminal and the second terminal of the secondary winding of the first transformer. The antenna is a differential antenna.