Focal cloud

Lens-reflector artifacts, geometry and other imperfections determine the actual diameter of the focal cloud.

The imperfections of the antenna lead to two problems: On the one hand the more the radio waves are directed away from the phase center of the feed horn, the more attenuated they get coupled into the waveguide.

On the other hand, the more the distance between antenna surface and feed horn varies, the bigger the phase shift gets - the closer the phase shift gets to 180 degrees (half a wavelength) between different parts of the antenna surface, the more the signal gets extinguished (attenuated).

[citation needed] For countering the effect, there are several techniques, either in construction of the reflectors or lenses, or in the way signal beams are concentrated.

Ground based dish antennas might benefit from minor deformation, producing a footprint encompassing satellite tidal motion.