In this study, an ultra wide band (UWB) antenna which radiates at 3.4-15.5 GHz is designed. The patch of the antenna is designed asymmetrically and the effect of the asymmetric structure to radiation performance is examined. The size of the antenna is 28x35 mm and the fractional bandwidth is 128%. The radar cross section of the designed antenna is reduced by modifying the physical structure. RCS of the antenna is reduced up to 15 dB. The proposed antenna is fabricated and the experimental results of the radiation performance are in a good agreement with the simulation results.