A previous study of a novel technique to design a band-reject UWB monopole antenna by using patch loading is extended. Frequency-domain measurements have confirmed that the antenna designed using this technique rejects the interfering signal at the two intended narrowband frequency ranges. Moreover, the antenna radiation pattern distortion is negligible except at the notched bands. A study of time-domain characteristics based on the antenna pulse response and system fidelity factor is presented. The time performance has been extracted from frequency-domain measurements using a standard method. The obtained time-domain results promise the suitability of the proposed technique to design band-reject antennas useful for future UWB system applications.