Design and performance measurements of a monopole antenna with modified ground plane for ultra-wideband application is proposed. The proposed antenna has y-shape patch to provide wider bandwidth. The ground plane located at the bottom layer is modified with truncated corners and double rectangular slot to have better matching impedance. The patch and ground plane of the antenna are etched on FR4 substrate with an overall size 39 mm × 40 mm × 1.6 mm. The results of the simulation show that the antenna operates with return loss less than-10 dB over the frequency band from 2.97 GHz to 11.54 GHz. Return losses of-58.81 dB for the resonant frequencies at 4.2 GHz can be achieved when the depth of the diagonal cut is 3 mm. The dimension of each rectangular slot is 12 × 5 mm, and rectangular notch size is 3 × 3.64 mm, providing a 14.1% wider bandwidth than ultra-wideband standard.