Abstract: In this paper, a slotted ridge waveguide antenna array(SRWAA) with high-gain and low-sidelobe and a center frequency of 24.125 GHz is proposed, consisting of an eight-way feeding network and an 8×40 radiating slot with a dimension of 400 mm×65 mm. The expected excitation distribution for the antenna array is extracted by beam synthesis method. By using a cut-off-mode power divider, the power ratio can be flexibly controlled. The sidelobe level(SLL) and half-power beam width(HPBW) in elevation plane are −20.9 dB and 54.5°, and the SLL and HPBW in azimuth plane are −27.8 dB and 2.5° respectively, and the peak gain is 23.2 dBi by using 3D electromagnetic simulation software HFSS. The simulation results are in good agreement with the theoretical analysis. The SRWAA can realize wide-sector beams with low-sidelobe at the same time, which covers a wide detection range and mitigate the interference from other directions. This work has the potential to be applied to air detection, antidrone, meteorological radar, and imaging radar.