On Dec 5, 8:17*pm, "Peter O. Brackett"
wrote:
Group:

Warning... this could be mind blowing!

Conventionally electromagnetic wave 'polarization' refers to the relative
physical spatial orientation of the electric field vector (E) of an
electromagnetic wave.

It is commonly understood that polarization of electromagnetic waves may be
either linear or circular.

Linear Polarization (LP):

Of course waves that are linearly polarized may have any arbitrary
orientation angle (theta) with respect to a reference frame such as the
earth's surface. *For example most common linear amateur antennas produce
and/or respond to waves of linear polarization, and these antennas produce
either either horizonally or vertically polarized waves depending upon the
orientation of the (linear) antenna with respect to the earth's surface
(ground).

As examples; a 1/2 wave length dipole for 10 meters hung at 30 feet between
two trees of equal height produces a largely horizonally polarized wave and,
a 2 meter 1/4 wave dipole mounted in the center of the roof of an automobile
produces a largely vertically polarized wave.

Of course as electromagnetic waves are propagated throughout an environment
are never purely orientated and usually contain an ensemble of many
orientations, because the waves are reflected from the ground, trees,
buildings, mountains, bridges, moving vehicles, and sometimes propogated
through moving and anisotropic media such as the ionosphere, etc... and so
the multiple reflection surfaces at various angles to the earth's surface
and/or refractions and Faraday rotations will conspire to "mix up" the
original orientation of the E vector of a purely linear transmitted wave and
usually produces a quite mixed polarization at distance from an emitting
antenna.

Malus' Law {I = Io [cos(theta)]^^2} describes the response of a linearly
polarized receiving antenna to waves arriving at a polarization angle theta
relative to the receiving antenna's preferred orientation. *i.e a
horizontally polarized antenna will produce maximum response to horizontally
polarized waves and a minimum response (zero) to a vertically polarized wave
and vice versa.

Of course in practice, because of the multipath reflections and refractions
the 'cross response' is never exactly zero or maximum as predicted by Malus
Law.

Just the same it is preferable to have the orientation *of a receiving
antenna 'aligned' with that of a particular transmitting antenna. *In the HF
region it is difficult for hams to "rotate" the orientation of their
receiving antennas to maximize signal pickup based upon polarization, and so
most hams are forced to take whatever response their relatively fixed
antennas produce to the relatively unknown orientation of received waves.

In military or commercial installations, where money and space may not be an
issue, either electronically or mechanically derived spatial antenna
polarization diversity can be utilized to maximize received signal strength
based upon arriving polarization. *Polarization diversity receivers...

Circular Polarization (CP):

Circular polarization describes the condition when an electromagnetic wave
is spinning or rotating with around its direction of transmission. *That is
the electric vector (E) of a circularly polarized electromagnetic wave is
rotating with an angular velocity as the wave travels through space. *This
is in contrast to the E vector of a linearly polarized wave which merely
oscillates in one linear direction.

Just as with linear polarization (horizontal and vertical) there are two
different distinctly possible orientations for circularily polarized waves,
these are known as Right Hand Circular Polarization (RHCP) and Left Hand
Circular Polarization (LHCP). * There are actually two well known
conventions used to label R and L CP depending upon the community of
interest, *namely physics/optics and electrical/electronics. *Usually
electronics folks refer the direction of rotation to the rotation of the E
vector around the direction of travel from a transmitting antenna, whilst
the optical physicists refer the rotation of E around the direction of
travel towards a receiving lens. *It's the same as the definition of up and
down, it's all in the eye of the beholder. *Regardless there are two
orientations for CP

Apparently circular polarization is less commonly known and understood than
linear (horizontal/vertical) polarization especially among hams.

There exist RHCP antennas and there are LHCP antennas. Perhaps one of the
easiest forms of CP antennas for hams to understand are the axial mode helix
antennas first discovered/studied by the great radio astronomer/ham John
Kraus W8JK. *Axial mode helix antennas may be "wound" with either a right
hand thread or a left hand thread.

Again Malus Law applies, in an easily applied modified form and so... RHCP
receiving antennas respond to RHCP waves and *LHCP receiving antennas
respond to LHCP waves. *A purely RHCP antenna will produce zero response to
an LHCP wave, etc...

An interesting effect happens upon reflection of CP waves. *An RHCP wave
reflected from a perfectly reflecting surface returns (is echoed) as a LHCP
wave!

CP propagation is often used in Satellite communications where a satellite
may use both RHCP and LHCP transmitting antennas on the same frequency for
communicating independently with two different ground stations using R and L
CP *antennas on the same frequency. *CP frequency diversity doubles channel
capacity!

Yet another common form of CP antenna uses crossed linear antennas fed with
a 90 degree (Pi/2) phase difference excitation.

As far as I know all currently known CP antennas such as axial mode helixes
and crossed 90 degree linear arrays produce CP waves where the angular
velocity of rotation is one revolution per cycle of the RF carrier, or in
other words one radian of circular rotation for each radian of frequency
transmitted. *In other words most well known CP antennas produce ONLY
synchronous CP, where the angular velocity of rotation of the E vector is
synchronized exactly with the frequency of the wave being transmitted.

I believe that the well known and understood situation of purely synchronous
CP is NOT necessesarily the only form of CP.

Warning... The following may be an invention!

Consider the case of a linear antenna, say a dipole, fed from a feed line
over rotating slip rings, such that the antenna can be rotated while it is
transmitting.

Now transmit on that dipole antenna whilst mechanically spinning it
clockwise [RHCP?] (with a mechanical motor of some kind).

The dipole antenna is linear and thuse emits linear polariztion, except it
is mechanically spinning, and so the E vector emanating from the antenna
will be rotating with respect to its direction of travel.

In this case the angular velocity of the motor that spins the linear antenna
need not be synchronous with the frequency being radiated.

For example we *could mechanically spin the antenna at 330 rpm while
transmitting a carrier of 1 GHz.

This would most certainly produce circular polarization. *For is not the E
vector spinning at 330 revs!

In fact the astute newsreader may note that we need not use a motor to
rotate the antenna. *In fact, I can propose several ways of "electronically"
rotating the linear antenna at any arbitrary angular velocity, not
necessarily synchronous with the transmitted frequency and so produce a
so-called non-synchronous CP at any desired rate of rotation.

Clearly, according to Malus Law, the maximum response to the non-synchronous
CP received waves from this 'rotating' antenna contraption would be from a
similarily rotating receiving antenna!

Question?

What would be the response of an axial mode helix antenna or say crossed 90
degree fed dipoles or any other "synchronous" CP antenna to such a
non-synchronous wave produces by a rotating antenna?

Would the response of a syncrhronous axial mode helix be less than that of a
sympathetically rotating receiving antenna?

What?

Thoughts, comments?

-- Pete K1PO
-- Indialantic By-the-Sea, FL
Pete Said,
"Circular polarization describes the condition when an electromagnetic
wave
is spinning or rotating with around its direction of transmission.
That is
the electric vector (E) of a circularly polarized electromagnetic wave
is
rotating with an angular velocity as the wave travels through space.
This
is in contrast to the E vector of a linearly polarized wave which
merely
oscillates in one linear direction."

Pete, I believe this is your error in thinking,instead of a a
spinning field perhaps it would be better just to few it as a coil
moving towards you with no rotation.

Jimmie