Abstract: In this paper, a slotted ridge waveguide antenna array(SRWAA) with high-gain and low-sidelobe is proposed, which can realize wide-sector beams with low-sidelobe at the same time. The proposed antenna can cover a wide detection range and avoid interference from other directions. 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. An SRWAA at 24.125 GHz is designed, consisting of an eight-way feeding network and an 8×40 radiating slot with a dimension of 400 mm×65 mm. 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°, at the center frequency, respectively, by using 3D electromagnetic simulation software HFSS. The peak gain is 23.2 dBi at 24.125 GHz. The simulation results are in good agreement with the theoretical analysis. This work has the potential to be applied to air detection, antidrone, meteorological radar, and imaging radar.