A Co-Planar Waveguide fed circular ultra-wide band antenna with modified ground-plane and feedline is designed on a FR4 (ϵr=4.3) substrate of thickness 0.01λ0. The proposed antenna exhibits an overall impedance bandwidth ranging from 2.99 GHz to 18.0 GHz and beyond (with S11< -10 dB). Design parameters have been optimized to achieve the UWB bandwidth. The measured radiation patterns of this antenna are omnidirectional in H- plane and bidirectional in E-plane. An extended impedance bandwidth is achieved as a result of modified feed-line. The proposed antenna can be used for medical imaging and urban IoT applications.