DUAL FREQUENCY ANTENNA

A dual frequency antenna comprises: a helix coil, of which the lower end is provided with a first resonant coil with a first pitch and of which the upper end is provided with a second resonant coil with a second pitch, for resonating at a frequency lower than the resonant frequency of the first resonant coil, wherein, the first pitch is larger than the second one; a first coupling unit, which is installed in the first resonant coil and is electrically isolated from the first resonant coil, for stabilizing resonant frequency performance of the first resonant coil; and a second coupling unit, which is installed outside the helix coil and is electrically isolated from the helix coil, for increasing equivalent electrical length of the first resonant coil and raising resonant frequency gain of the first coil. By the improvement of the two coupling units in the high frequency part of parts of the resonant structure in the present invention, better resonant frequency performance of the first resonant coil is obtained, thus centralizing performance of the first resonant coil to the upper hemisphere, increasing the distribution current of the first resonant coil, and at the same time increasing the electrical length of the first resonant coil.