A slot array antenna including a smooth curved surface and planar feed structures which are respectively disposed at two ends of the smooth curved surface and are tangent to the smooth curved surface. The smooth curved surface includes at least two arcs mutually connected by smooth transition. The at least two arcs each includes an upper copper metal layer, a lower copper metal layer, and a dielectric substrate layer between the upper and lower copper metal layers. The upper copper metal layer includes radiating slots, and the adjacent radiating slots in a linear array have opposite offsets along the center line of the slot array antenna. The dielectric substrate layer includes metallic vias symmetrically arranged on both sides of the central line of the antenna to form a substrate integrated waveguide.