The appearance of incommensurate modulations in perovskite antiferroelectrics (AFEs) has been experimentally observed and challenges the established models like the Kittel sublattice model which relies on the assumption of a supercell with the up-down polarization configuration. In this talk we present a high oder gradient phase-field model for antiferroelectrics, which allows theoretically modeling of any modulation, even non-equally modulated cases. The phase-field model enables also the AFE-FE phase transition and double-hysteresis under external stimulie including electric and mechanical fields and temperature, as well as in the presence of defects like grain boundary and point defects. It includes also parameterization through physical quantities relevant to the antiferroelectricity. The capability of the model will be demonstrated through numerical simulation results and comparison to experimental data.