Abstract: A resistor loaded ultra wideband (UWB) TEM horn antenna is presented, which consists of two smoothly tapered metal sheets. A microstrip feeding network is adopted for the simple coaxial cable and the resistive loading technology is introduced to eliminate the reflected wave caused by the impedance mismatching between the antenna aperture and free space, which effectively improves the low frequency characteristic and expands the bandwidth. Based on the theoretical anal ysis, one prototype of the antenna is designed and fabricated, the experimental results show that this antenna has a 50:1 im pedance bandwidth in the full band range from 0. 1GHz to 5GHz for VSWR<2 and good transmission characteristics over the frequency range from 0. 75GHz to 5GHz.