An ultra wideband antenna (20) is disposed on a substrate (10). The substrate includes a first surface (101) and a second surface (102). The ultra wideband antenna includes a radiation body (22), a feeding portion (26), and a grounded portion (28). The radiation body disposed on the first surface is used for transceiving electromagnetic signals. The radiation body includes a semicircle-shaped metal portion (222) and a rectangle-shaped metal portion (224) and defines a slot (24) starting at an edge therein. The feeding portion is electronically connected to the radiation body for feeding signals to the radiation body. The grounded portion is disposed on the second surface.