Question

Which type of feed in parabolic antenna blocks the beam limiting aperture efficiency to 55%?

(a) Axial feed

(b) Offset feed

(c) Cassegrain

(d) Gregorian

The question was posed to me in unit test.

I'm obligated to ask this question of Application of Parabolic Reflector topic in portion Reflector Antenna of Antennas

Answer 1

Right option is (a) Axial feed

For explanation I would say: In Axial feed, the feed is located at the focal point along the beam axis infront of dish and is pointed back and blocks some part of beam. Offset is used to avoid the aperture blocking. In Cassegrain and Gregorian the aperture efficiency is approximately 70%.