This paper introduces a compact modified semi-circular monopole ultra-wideband (UWB) antenna. A compact antenna size (4.3 × 3.4 cm2) compared to the typical coplanar waveguide (CPW) circular monopole antenna (5.5 × 4 cm2) is achieved. The proposed antenna is completely proven for UWB communication performance. The antenna is matched over 8.4 GHz bandwidth (2.2–10.6 GHz), with reflection coefficient lower than −10 dB over the band. Matching bandwidth is verified through simulation and measurements of VSWR. Efficient power radiation over the band is proven through radiation efficiency. Radiation efficiency is not lower than 81% at the upper end of the band. Omnidirectional characteristics are proven through, firstly, measured transfer function magnitude at three different configurations, Face-to-Face, Face-to-Side, and Side-by-Side (all frequencies at different orientations), and, secondly, measured radiation pattern at three selected frequencies that span the bandwidth (all orientations at different frequencies). Moreover, the ability of the antenna to support, as narrow pulses as, 0.25 ns omnidirectionally is proven through detailed study for time response. Antenna transfer function is measured for magnitude and phase. Then, a first-order Raeighly pulse, that fulfils the FCC mask for emission restrictions, is applied at the terminals of a UWB system of the proposed UWB antenna. Finally, the output, barely distorted, normalized, pulse is compared to the input pulse.