This study introduces a high-accuracy beam pattern synthesis technique using comprehensive unit cell and near-field measurement environment modeling for a miniaturized 8×8 transmitarray antenna with a unit cell period of 0.4λ 0 . The unit cell comprises transmitting and receiving antennas, a single pole double throw PIN diode switch, and a two-stage reflection-type phase shifter. This beam pattern synthesis methodology integrates measured data from individual unit cell components, coupled with simulations of a simple feed antenna and an infinite array transmitting antenna. This approach enables precise prediction of the transmitarray's beam pattern and overall performance, effectively circumventing the need for extensive finite array full-wave electromagnetic simulations. Notably, the calculated beam pattern closely aligns with the experimental results with high accuracy.