Diffraction and pattern perturbation effects in offset Gregorian reflector antennas with wideband feeds

The offset Gregorian reflector system of the Square Kilometer Array radio telescope is required to operate with wideband feed (WBF) antennas down to very low frequencies, where reflectors become (electrically) relatively small. The considered WBF technologies are the log-periodic (Eleven) antenna and the quadruple-ridged flared horn. This paper investigates some of the performance degradation effects that are specific for the low frequencies and typical for these WBFs, including the feed pattern perturbations and diffraction. Several performance metrics, such as the antenna receiving sensitivity and side lobe levels are considered.