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