This letter presents a directive integrated-antenna-source (DIAS) for a high-power ultrawideband parabolic reflector system. Unlike the previously developed omnidirectional integrated-antenna-source (OIAS) that leads to spillover loss in a high-power parabolic reflector system, the proposed DIAS reduces the spillover loss in the system. The DIAS is designed by cutting away the halves of the two electrodes in the OIAS. The DIAS-based reflector system was designed through numerical electromagnetic simulations. The proposed DIAS was fabricated for validation. The proposed DIAS shows 3 dB beamwidths on the H-plane and E-plane of 234 degrees and 116 degrees, respectively, in the peak electric-field patterns. In addition, the DIAS has a much smaller capacitance than the OIAS. The proposed DIAS-based reflector system has a peak electric-field strength of 39.5 kV/m at a distance of 40 m. The results show that, although the DIAS has a much smaller capacitance than the OIAS, the DIAS-based reflector system is capable of producing high-power electromagnetic pulses similar to those of the OIAS-based reflector system.