Dual frequency band planar micro-strip antenna

To meet the requirements including dual operation frequency bands, a high gain, and a broadside radiation formation, a dual band planar micro-strip antenna utilizing antenna array is provided. One array element includes a rectangle-shaped micro-strip antenna and an arrow-shaped micro-strip antenna. A first resonance frequency is determined by a length of the rectangle-shaped micro-strip antenna. Fillisters are dug for satisfying a second resonance frequency. Curve surfaces of the arrow-shaped micro-strip antenna designed by ellipse formula so that a frequency resonance is reached under both the first resonance frequency and the second resonance frequency, and a broadside radiation formation is thus generated. A T-shaped junction distributes power between antenna arrays according to the output impedances of the antenna array. L-shaped band-stop filter located on the T-shaped junction is utilized to restrain frequency resonance resulted from multiples of the first resonance frequency.