Question

Which of the following condition holds good for minimum total aperture blocking in Cassegrain?

(a) Area of sub-reflector and projected area of feed are equal

(b) Area of primary reflector and projected area of feed are equal

(c) Area of sub-reflector greater than area of primary reflector

(d) Area of sub-reflector is less than projected area of feed

Answer 1

Correct choice is (a) Area of sub-reflector and projected area of feed are equal

The explanation is: Minimum total aperture blocking occurs when the area of sub-reflector and projected area of feed are approximately equal. In other conditions, the main ray back radiated ray gets added up with collinear rays from the primary reflector.