An antenna structure includes a substrate, a plurality of reflective plates, a grounding plate, a radiating member and a plurality of conductive vias. The substrate contains liquid crystal polymer and has opposite first and second surfaces. The reflective plates are arranged in an array on the first surface of the substrate. The grounding plate is arranged on the second surface of the substrate and overlaps with the reflective plates in a normal direction of the substrate. The radiating member is on the second surface of the substrate and does not overlap with the reflective plates in the normal direction of the substrate. The radiating member has an open slot which is defined by a first radiating branch and a second radiating branch that generate at least two different operating frequency bands. The conductive vias respectively penetrate the substrate and connect with the reflective plates and the grounding plate.