Talk:Cassegrain antenna

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A very important antenna in need of some more information which I hope to add but will be a few weeks/months somebody may wish to add earlier. I think the following needs adding: The reflector surface profiles/geometry (I think parabolic for the main and hyperbolic for the subreflector).

For the cassegrain of course the focus of the main reflector should coincide with one of the focii of the subreflector such that the concave surface of the main faces the convex surface of the sub. It should link to the gregorian antenna for which it uses the other focus of the sub.

Problem: obstruction of the beam by the subreflector and structure holding it: also scattering which causes sidelobes. f/d ratio.

Coherent phase at the aperture (but distorted by the varying incident angles.

Allows a relatively simploe feed from behind the main reflector (eg. a small waveguide horn antenna or beam waveguide.

It was derived from the equivalent cassegrain optical telescope based on the same principle. There is an IEEE/IRE paper by Hannan I believe but I have lost mine.

The aperture needs to be much greater than the wavelength or diffraction causes big sidelobes. ChrisAngove 19:08, 12 November 2006 (UTC)