A dielectric resonator antenna (DRA) with a full ground plane and an ultrawideband (UWB) operating bandwidth of 3.1-11.6 GHz is presented. Good return loss over a wide bandwidth is achieved, while the full ground plane directs most of the radiation into the upper hemisphere, significantly reducing undesirable radiation to the lower hemisphere. The measured results confirm a 10-dB return-loss bandwidth of 115%. Time-domain characteristics and effective isotropically radiated power (EIRP) spectra of the antenna are investigated for several types of UWB input pulses. The correlations between the input pulses and the radiated pulses in many directions were found to be excellent when the antenna is excited by a linearly chirped Gaussian pulse or a fifth-order Gaussian pulse. Nevertheless, EIRP spectrum calculations indicate that none of those pulses efficiently fill the Federal Communication Commission UWB mask when applied to this DRA. Hence, a third-order Rayleigh pulse is introduced and tuned to make efficient use of the allowed spectrum limits. Further improvement of pulse performance is investigated by varying antenna design parameters. This DRA is suitable for both impulse radio UWB systems and carrierbased UWB systems.