We report on the numerical analysis of Bragg polarization gratings (PGs), especially those formed with liquid crystals, and study their general diffraction properties by Rigorous Coupled-Wave Analysis (RCWA). Different from traditional Bragg (isotropic) gratings, Bragg PGs are verified to have high diffraction efficiency for large field of view, which is ideal for exit-pupil-expanders in waveguide-based head-mounted-displays, spectroscopy, and fiber-optic telecommunication systems. The RCWA approach allows for a rigorous and accurate solution without paraxial approximations to be obtained with much lower computational cost and time, as compared to finite-element, finite-difference, or analytical coupled-wave approaches. Therefore, it enables the study of the complete transmittance and reflectance behavior of Bragg PGs in the most computationally efficient way. Diffraction characteristics including angular response and polarization sensitivity are investigated. The spectral response and thickness dependence are also examined.