Subreflector illumination patterns on the main reflector as a function of angle θ_p from z_p, the direction from PF to the center of the primary, for three values of φ_p in the main reflector (“p”) coordinate system: φ_p = −90°, red; 0°, green; 90°, blue. Vertical lines indicate the near () and far edges () of the main reflector in the φ =  ± 90° half-planes, respectively.