Abstract: A slotted waveguide array antenna operating at S band for transmitting high power microwave is developed in this paper. The profile height is reduced by arranging the coupling waveguide and feeding waveguide on same layout. The coupling slots with same offsets direction and the radiating slots arranged regularly compensate phase, which achieves in-phase superposition of pattern of slot units. The influence of different slot parameters and types of divider on power capacity of the antenna are simulated. 0.1 MPa SF₆ gas is filled in the sealed antenna to enhance power-handling capability. The simulated and test results show that the antenna has a 6.7% bandwidth with VSWR less than 1.5 and a gain up to 27 dBi. Hot test of this antenna is carried out fed by narrow-band high power microwave source. The transmitted waveform and the output one agree well. The measured output power of the source is 2.67 MW.