In this paper, a broadband micro-strip patch antenna is designed and manufactured, which is comprised of many substrates with different thickness and dielectric constants. This antenna is fed, through the coupling slot, by a semi-annular micro-strip line. The simulated and tested results show that the 47% impedance band (VSWR<2) and 8.4dB gain are achieved. This antenna can be widely used in the field of broadband plane array antennas.