Using a subnanosecond high-voltage modulator with a pulse repetition frequency of up to 100 pps, we have carried out experimental research into the excitation of ultrabroadband TEM antennas. The modulator consisted of a RADAN-303B nanosecond driver and a pulse sharpener based on gas spart gaps. The device was capable of generating single-polarity and monocycle pulses with readjustable duration and amplitude. The amplitude and power of the pulses supplied to the antenna ranged up to 100 kV and 200 MW, respectively. Preliminary data have been obtained on the stability of modulator subnanosecond pulse parameters under conditions where the amplitude dispersion of nanosecond-driver pulses is on the order of 5%. Results are provided for the electric strength of the matching junction between the modulator and the antenna. The ultrabroadband pulse was recorded at distances of up to 25 m. Its characteristics permitted spatial resolution of reflections from conductive objects with a shape nonuniformity scale of no more than 25 cm. Radiators with increased directivity in the E or H (E and H) plane were explored. Such radiators incorporates two (four) TEM antennas energized by a split modulator pulse. Consideration is given to versions of phased and opposite-phase antenna connection.