Low frequency diffraction effects when shaping the offset gregorian reflector system of the SKA

The offset Gregorian reflector system of the Square Kilometer Array (SKA) radio telescope is required to operate down to very low frequencies, where reflectors become (electrically) relatively small. Shaping the reflectors to control the aperture distribution can improve the electrical performance of the system. Since the system is expected to operate over more than a decade of bandwidth, the shaping is performed using standard Geometric Optics methods. This paper systematically investigates the effects that diffraction will have at low frequencies on the performance of several performance metrics for a wide range of shaped geometries. It is shown that the peak position of the primary design objective, the receiving sensitivity, is relatively insensitive to diffraction effects, making such wide band shaped reflectors a viable option for the SKA