In this article, a slot array antenna with circular polarization is presented. The structure is designed based on GasperPeano fractal as a feed line. By use of the Minimum mean square error method, the array has been optimized for the best radiation power. First, the theory of a single feed line with a radiation element is presented, then extend this theory to the double and N radiation elements. At each step, the coupling factor and radiation power are calculated. And three error function is defined as goal functions for reaching uniform distribution, maximum efficiency and the combination of them. Due to the goal functions, a genetic algorithm is represented to reach the best results by altering and tuning the parameters. The circular polarization bandwidth of the final structure is 5%, and the radiation efficiency is 85%. This theory and structure can be useful for making circular polarization in applications. K E Y W O R D Santenna theory, circular polarization, fractal antennas, transmitting antennas, slot antenna