An antenna structure includes a ground plane and at least one series-fed antenna. Each series-fed antenna includes a first patch, a plurality of second patches, a first microstrip line, a first grounding structure group, a plurality of second microstrip lines, and a plurality of second grounding structure groups. The first patch is disposed beside the ground plane. The first patch and the second patch are arranged along a straight line. The first microstrip line extends from the first patch and has a feeding point. The first grounding structure group includes two first grounding traces that extend symmetrically from both sides of the first microstrip line to the ground plane. The second microstrip lines are respectively connected between the first patch and the second patches. The second grounding structure groups are respectively disposed on both sides of the second microstrip lines, and are coupled to the ground plane.