An antenna structure includes a microwave substrate, a main-antenna unit, an extension grounding unit. The main antenna unit is arranged on the surface of the microwave substrate. The main antenna unit includes a main-radiation portion, a main-feeding portion, a main-grounding portion. The extension grounding unit is arranged on the surface of the microwave substrate. The extension grounding unit includes a first extension grounding portion and a second extension grounding portion. The antenna structure can adjust the radiation pattern and improve the antenna directivity. The main-antenna unit and the sub-antenna unit share the extension grounding unit in common. So, the antenna structure can reduce the antenna occupied volume and save the mass production cost.