Cassegrain antenna

The Cassegrain is a more complex design, but in certain applications it has advantages over front feed that can justify its increased complexity: A disadvantage of the Cassegrain is that the feed horn(s) must have a narrower beamwidth (higher gain) to focus its radiation on the smaller secondary reflector, instead of the wider primary reflector as in front-fed dishes.

It is used in very large steerable radio telescopes and satellite ground antennas, where the feed electronics are too complicated and bulky, or requires too much maintenance and alterations, to locate on the dish; for example those using cryogenically cooled amplifiers.

The beam of incoming radio waves from the secondary reflector is reflected by additional mirrors in a long twisting path through the axes of the altazimuth mount, so the antenna can be steered without interrupting the beam, and then down through the antenna tower to a feed building at ground level.

The first Cassegrain antenna was invented and patented by Cochrane and Whitehead at Elliot Bros in Borehamwood, England, in 1952.

[6] The Voyager 1 spacecraft launched in 1977 is, as of September 2024[update], 24.6 billion kilometers from Earth,[7] the furthest manmade object in space, and it's 3.7 meter S and X-band Cassegrain antenna (picture below) is still able to communicate with ground stations.