Thermal and gravitational effects distort the surface of large reflector antennas and degrade the antenna pattern. When operating with electrically large reflector antennas the surface error limits the high frequency applicability. The behavior of the distorted reflector can be improved by using various techniques to compensate the reflector distortions. This communication presents a new physical optics based approach to synthesize shaped subreflectors to achieve such a compensation. The main contribution of the communication is that the method is not based in computationally intensive calculation nor optimization and thus presents very low calculation times when applied to large antennas. Representative results and comparison with previous approaches to the same problem are presented.