Results of the computer simulation and experimental study of high-power broadband microwave generator, based on H-waveguide are presented. H-waveguide was driven by the high-voltage dual spark gap. The spark gap is filled by the pressurized gas, serving as load of the dual forming line. The generator allows to obtain power in pulse up to 400-450 MW for the spectrum width Δω/ω ~ 0.5 and PRF up to 10 Hz.