On Sun, 13 Sep 2009 12:46:30 +0100, "christofire"
wrote:

Does one wave has many polarizations, or one antenna has many
polarizations? Which one: transmitter or receiver? Could you teach me?
A*


You appear to have changed your identity from S* to A* !

The answers according to the physics that real-life radio communication
depends upon, and was designed by, a


A much simpler, and compelling explanation:
what you see is what you get.

If it looks vertical, the polarization is vertical;
If it looks horizontal, the polarization is horizontal.

It thus stands to reason that if the radiator is U shaped you see both
horizontal and vertical - hence the full sphere filled with radiation.

This closes the simple answer, which of course drives a very lengthy
explanation - there is no such thing as a free lunch:

Now, I can well anticipate some wag pointing out that they are
standing, looking at these "goal posts" edge on and see only the
vertical supports. "There is no horizontal view - no horizontal
polarization. It can't be isotropic!"

Of course it can't; and yet the vertical radiation fills the null of
the horizontal (and likewise, the horizontal fills the null of the
vertical). Total field is spherical.

What does this make of a tilted radiator? What you see is what you
get. At some perspectives it looks goofy horizontal AND it looks
goofy vertical. In other perspectives it just looks vertical. As Art
might protest: "Never mind goofy, how much horizontal?" If we reduce
this to a number of goofiness, a trig function would serve quite well.
Most students who were trained in mechanics would recognize the method
to deconstruct an angle into its two, XY, components. If the tilt
were 45 degrees, in full view of that angle you must experience the
single antenna as having two equal vertical and horizontal
contributions to radiation. If it were tilted 30 degrees, obviously
one polarization would dominate over the other. Ground would compound
the issue, but would not negate the general principle.

This last part returns us to the discussion of isotropism which
encompasses the topic of Lambert's Law which is generally confined to
a black body radiator (or the sun from a great distance as it fails to
be isotropic in the near view, such as we have here on earth). Few
here need concern themselves with this unless they are making patch
antennas. However, within the discussion above, the topic of view,
angle, and radiation contribution are wrapped up in Lambert and
cosine.

73's
Richard Clark, KB7QHC