"Peter O. Brackett" wrote in message
m...
Roy:

[snip]
"Roy Lewallen" wrote in message
treetonline...
Dave wrote:

Circular polarization means you have equal H-Pol and V-Pol radiation,
with one polarization 90 degrees ahead (or behind) of the other.
.
.
.
That's not a very good description, although it's correct. But here's a
little more complete description: The electric (E) field of a
horizontally polarized wave is horizontal, and the E field of a
vertically polarized wave is vertical. But the E field of a circularly
polarized wave rotates at the transmission frequency, one revolution per
cycle. The instantaneous amplitude of a vertically or horizontally
polarized field is sinusoidal, varying at the transmission frequency. The
amplitude of a circularly polarized wave is constant.
[snip]

Hmmmm....

Roy, I don't believe that is a "complete" description of circular
polarization either.

My understanding is that circular polarization is what we call the
polarization of electromagnetic radiation when the electric field vector E
rotates with an angular velocity rather than oscillating back and forth in
a single (linear) direction.

Roy, your description of circular polarization above seems to imply that
the angular velocity of the E vector of a circularly polarized wave is
always "synchronized" with the signal frequency since you stated that it
rotates at one revolution per cycle, or one radian per radian per second.

This of course is the (normal?) situation if the antenna is say a helix
firing along its axis or say crossed dipoles fed with a 90 degree phase
shift, but... to be more complete, we should note that...

Circular polarization does not have to be "synchronous"!

Consider...

What would you call the polarization type of the radiation emitted by the
following radiator?

An ordinary linear dipole fed with RF from a feedline through two slip
rings arranged such that a mechanical drive is able to rotate the dipole
at some arbitrary mechanical angular velocity completely unsynchronized
with the RF carrier.

For example, say it's a 5m dipole driven with 30MHz carrier signal and
mechanically rotated at 1000 revolutions per minute.

Such an arrangement would result in circularly polarized radiation with
the E vector having angular velocity of 1000 revolutions per minute and a
carrier frequency of 30MHz which definitely is not one revolution per
cycle.

Thoughts, comments?

--

Pete
Indialantic By-the-Sea, FL

Hi Pete

Your idea of rotating a linearly polarized 30 MHz dipole at 1000 RPM does
not relate to the term "Elyptical Polarization" which is often called
Circular Polarization. The Wikipedia information is fairly complete as it
defines CP..

Jerry KD6JDJ