A near field antenna adapted to an object detecting device, for sensing a plurality of units under test of at least an object under test. The near field antenna comprises a periodic guided-wave structure, a metallic reflection portion and at least two near field magnetic coupling antennas. The periodic guided-wave structure disposed below the object under test has a plurality of conductive units periodically arranged on a first plane. The metallic reflection portion is disposed under the periodic guided-wave structure to form an enclosed space. The near field magnetic coupling antennas are disposed on a second plane parallel to the periodic guided-wave structure, and are located in the enclosed space. The feed point and the ground point of each near field magnetic coupling antenna are fed by a coaxial cable with a feeding direction parallel to the periodically arranged conductive units.