In this report the performance of the hard horn antennas in a cluster-fed offset reflector system operating in the Ka-band (20-30 GHz) is analyzed. The analysis is done with a program that uses aperture integration to find the far-field of the antenna system. The results for different positions of the feed antenna in the offset reflector system are compared with results obtained for a rotationally symmetric antenna with the same diameter and a focused feed (BOR1 approximation). The results show a good agreement for the focused feeds and some differences as the feed is displaced from the focal point. Several improvements of the reflector design are proposed and analyzed. It is concluded that the BOR1 approximation is a powerful tool when designing a cluster-fed offset reflector system. Especially in the initial stage it gives the possibility to test a large number of different reflector designs. However, there are also degradation in the co- and crosspolar isolation for off-focus feeds that can only be studied by locating the feed in its real off-focus position in the actual offset reflector.