A new type of ultra-wideband (UWB) printed monopole antennas is presented, which is composed of a circular or annular patch and a trapeziform ground plane with a tapered CPW feeder in the middle. Both simulated and experimental results are presented,showing good agreement and therefore verifying validity of the design. The proposed antenna with a circular monopole patch achieves an 11.6: 1 measured ratio bandwidth of VSWR ≤ 2 ( from 0.79 GHz to 9.16 GHz), while that with an annular patch obtains a measured ratio impedance bandwidth of 10.6:1 (from 0.87 GHz to 9.47 GHz). In addition, these designs exhibit nearly omnidirectional radiation patterns with simple compact structures, which are attractive in communications and others UWB applications.