다. AbstractThis paper presents a dual-band array antenna based on a modified Sierpinski fractal structure. Array structure is mirror symmetric, and forms broadside radiation pattern for dual frequency band if the ports are fed with 180° phase difference between upper and lower 2×1 array. To use in-phase corporate feeding circuit, the phase inversion structure is designed by changing the position of patch and ground for upper and lower array. The dimensions of the array antenna is 28×30×5 cm 3 and the bandwidth of 855～1,380 MHz(47 %), 1,770～2,330 MHz(27 %) were achieved for -10 dB return loss. The measured gain is 9.06～12.44 dBi for the first band and 11.76～14.84 dBi for the second band. The half power beam width is 57° for x-z plane and 46° for y-z plane at 1,100 MHz and 43° and 28° at 2,050 MHz, respectively.