Focal cloud: Difference between revisions

Content deleted Content added

Inline

Revision as of 03:17, 4 May 2008

A focal cloud is the collection of focal points of any imperfect lens, whether optical, electrostatic or electromagnetic. This includes Parabolic antennas and lens-type reflective antennas of all kinds.

In this focal cloud illustration, a perfect reflector would focus all beams into the blue spot. Due to imperfections of lens construction, the actual signal beams follow the red path to several different focal points, which form the focal cloud. Lens-reflector artifacts, geometry and other imperfections determine the actual radius of the focal cloud.

Satellite dish effects

A focal cloud can render a satellite dish rather inefficient in relation to its size in specific frequencies. If the imperfections are formed in a way that the phase shifts of reflected waves, at a large portion of the dish, are near 180 degrees between them and the feed horn, this results in self-cancellation of the specific frequency.

For countering the effect, there are several techniques, either in construction of the reflectors or lenses, or in the way signal beams are concentrated. In Satellite antennas, scalar rings are used to push the spread signal into the Feed.

References:

|Satellite LNB's & polarizers

@@ Line 1: / Line 1: @@
-[[Focal cloud]] is a general definition referring to the [[focal point]] of an ''imperfect'' lens,
+A [[focal cloud]] is the collection of [[focal point]]s of any ''imperfect'' lens,
 whether [[lens (optics)|optical]], [[Electrostatic lens|electrostatic]] or electromagnetic.  This includes [[Parabolic antenna]]s and lens-type reflective antennas of all kinds.
 [[Image:Focal cloud.jpg]]
-In this focal cloud illustration, a perfect reflector would focus all beams into blue spot.  Due to imperfections of lens construction, the actual signal beams follow the red path to several different focal points, which form the focal cloud.  Lens-reflector artifacts, geometry and other imperfections determine the actual radius of the [[focal cloud]].
+In this focal cloud illustration, a perfect reflector would focus all beams into the blue spot.  Due to imperfections of lens construction, the actual signal beams follow the red path to several different focal points, which form the focal cloud.  Lens-reflector artifacts, geometry and other imperfections determine the actual radius of the [[focal cloud]].
 == Satellite dish effects ==
-Apart for satellite dish performing worse than expected due to the effect, focal cloud can even render a satellite dish rather inefficient in relation to its size in specific frequencies if the imperfections are formed in a way that the [[phase shift]] of reflected waves at a large portion of the dish is near 180 degrees between them near the center of the cloud,where lies the [[feed horn]] thus resulting to self-cancellation of the specific frequency.
+A focal cloud can render a satellite dish rather inefficient in relation to its size in specific frequencies. If the imperfections are formed in a way that the [[phase shift]]s of reflected waves, at a large portion of the dish, are near 180 degrees between them and the [[feed horn]], this results in self-cancellation of the specific frequency.
 ----
-For countering the effect, there are several techniques, either in construction of the reflectors or lenses, or in the way signal beams are concetrated. In Satellite antennas, [[scalar rings]] are used to push the spread signal into the [[Feed horn|Feed]].
+For countering the effect, there are several techniques, either in construction of the reflectors or lenses, or in the way signal beams are concentrated. In Satellite antennas, [[scalar rings]] are used to push the spread signal into the [[Feed horn|Feed]].
 References: