A novel ultra-wide band antenna is proposed.The cross structure and composite circular curve were investigated to improve both the impedance bandwidth and radiation patterns.The proposed antenna was modeled and simulated in CST software.The results demonstrate that the antenna can work well in(0.47—25.5)GHz,with return loss better than-10 dB.The radiation patterns of the proposed antenna keep stable within the whole band.Out-of-roundness of the H plane is better than –5 dB.The proposed antenna shows great v...