Abstract: The radiating characteristics of apertures excited by step and Gaussian pulses are presented in this paper. The relationships of the incoming pulse width, the size of the aperture, and the location of the observer are analyzed. The radiating characteristics of apertures excited by Gaussian pulse are thoroughly investigated. Along the radiating axis, several regions, each bearing somehow unique radiating properties, can be divided as radiating farfield region, transit region, and nearfield region in order to describe the behavior of an ultrawideband (UWB) aperture antenna.