The impact of an azimuthal slot in the antenna flair on the performance of a bowtie antenna has been analyzed. It has been shown that the slot is equivalent to resistance-capacitance loading. The resistance of the slot is physically caused by radiation of electromagnetic energy from the slot. Equivalent resistance and capacitance of the slot have been analyzed against geometrical parameters and frequency. The azimuthal slot has been used to improve the bowtie performance and to optimize this antenna for an ultrawideband impulse radio system under development. After optimization, the antenna exhibits a better performance than the conventional bowtie in terms of efficiency, late-time ringing, and matching to the generator/receiver. The performance of the optimized antenna has been verified experimentally; good agreement between theory and experiment has been observed.