Which of the following is NOT a valid parabolic dish illumination arrangement?

Parabolic dish antennas rely on specific feed arrangements to efficiently illuminate the reflector. Common valid configurations include front feed (prime focus), offset feed (where the feedhorn is moved out of the center to prevent signal blockage), and Cassegrain (which uses a convex sub-reflector). Newtonian, on the other hand, is a classic optical telescope design invented by Isaac Newton that uses a flat diagonal mirror. While both optical telescopes and radio dishes rely on parabolic reflectors, the Newtonian arrangement is not used for RF antenna illumination.