Abstract: In traditional high-power slotted waveguide arrays, the mutual coupling between the adjacent slots seriously affects the wide-angle scanning ability of the array. To improve beam scanning ability, the scanning characteristics of the array has been analyzed. An isolation barrier has been introduced into the traditional slotted waveguide array to suppress the cross polarization caused by the inclined slots and improve the isolation of the elements. In this paper, an antenna array based on the rectangular waveguide with resonant slot in the narrow-wall has been proposed and designed, the simulation results show that the traditional structure can only scan to ±34° when S₁₁≤−10 dB. But after loading the isolation barrier, the scanning range is expanded to ±45° with 2.3 dB gain reduction. Moreover, the power handling capacity of a single slotted waveguide is more than 330 MW, which indicates application potentials of this antenna in high power microwave (HPM) field.