Optimising the blocking efficiency in shaped Cassegrain systems

The blocking efficiency of a Cassegrain antenna system can be improved considerably by shaping the main and the subreflector in such a way that the power, which is normally lost by scattering against the blocking obstacles, arrives at the aperture in the correct phase and direction and with the correct amplitude. It is explained that shadows of (nearly) spherical waves on the aperture can be made to disappear entirely. A practical example is described.