A wide-band antenna mounted on a circuit board includes a ground plate, a radiating plate perpendicularly connected to two side edges of the circuit board, and a planar antenna element which includes a base plate, an extending plate, and a ground portion. One side of the base plate defines a gap with a first coupling portion being formed, and a slot adjacent to the gap with a first strip being formed therebetween. A second strip is extended perpendicularly from the first strip. The extending plate is extended outward from one end of the base plate. The ground portion is extended outward from the second strip and connected to the ground plate. The first coupling portion and the ground portion have an interspace to form a capacitive coupling therebetween. A groove is formed among the first and second strips and the ground portion to form a simulation inductance thereamong.