I hope to answer these questions and others with this article. Minimizing diffraction scattering by eliminating feed and feed spar blockage results in lower sidelobe levels. This elimination of blockage alsoresults in higher system efficiencies.
Higher efficiencies mean higher gain, which translates to a smaller reflector.
An offset reflector is a cut out section of a prime focus reflector. The parent reflector must be generated first, and then a section is defined that represents the area of the offset reflector. This cut out section generally extends from the center to the outer perimeter of the parent reflector. This cut out section Will appear as an ellipse to the end user. However, to the incoming microwave signal, the reflector appears as a circle.