An antenna includes a grounding portion with a grounding feed point, a radiating plane and a coaxial cable. The grounding portion extends in a lengthwise direction defining two ends opposite to each other in the lengthwise direction. The radiating plane extends upwardly from a lengthwise edge of the grounding portion. The radiating plane includes a first arm extending from one end of the lengthwise edge and a second arm extending from the opposite end. The first arm defines a signal feed point and a first radiating portion while the second arm is defined as a second radiating portion. The coaxial cable includes a core linking to the signal feed point and a shielding layer linking to the grounding feed point. The second arm surrounds the first arm in the radiating plane.