Derivation of monopulse angle accuracy for phased array radar to achieve Cramer-Rao lower bound is presented in this paper. Antenna element positions originating from antenna center are used for difference beam taper in this monopulse angle estimation. For uniform linear array, the accuracy is 1.16 times higher than conventional monopulse method. In other words, SNR can be reduced by 1.3 dB to achieve required angle accuracy. Suboptimal difference beamforming taper for the subarray-based digital beamforming radar is also derived.