An antenna structure includes a central grounding line and a spiral antenna. The central grounding line is linear and has two end portions provided with a grounding point and a first open point, respectively. The spiral antenna has two end portions provided with a feeding point and a second open point, respectively. The spiral antenna winds around the central grounding line while extending in the direction from the grounding point to the first open point, with the second open point positioned proximate to the first open point, wherein the spiral antenna and the central grounding line are spaced apart by an axial distance, thereby allowing the antenna structure to receive and transmit a radio frequency signal with circular polarization.