Circular polarization... does it have to be synchronous??
 

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

Circular polarization... does it have to be synchronous??
 

Peter O. Brackett wrote:
. . .
It is commonly understood that polarization of electromagnetic waves may
be either linear or circular.

Then some education is in order. Electromagnetic waves are elliptically
polarized. The two extreme special cases of this are linear and circular
(with axial ratio of zero -- or infinite depending on your choice of
definition -- and one respectively). There are an infinite number of
other possible elliptical polarizations with different axial ratios.

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).

Of course linear polarization can have any orientation, not just
vertical or horizontal. And even those terms lose meaning when away from
the Earth. However, it's often convenient to mathematically separate
waves into two superposed components of horizontal and vertical
polarization.

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.

The polarization of the dipole signal will be purely horizontal only
directly broadside. The signal off the ends are purely vertically
polarized, and in other directions neither horizontal nor vertical.

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.

By "mixed" polarization, I assume you mean a single polarization which
is neither horizontal nor vertical and can be described as a "mixture"
of a purely horizontal and a purely vertical wave.

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.

It's also difficult to get the polarizations of the antennas exactly right.

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.

There's no advantage at HF of having the antenna orientations the same
if the path is via the ionosphere.

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):

. . .

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...

Interesting. Can you work an example for us? I'm curious as to what you
use for theta in the "law's" equation.

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!

Only if it strikes the surface directly head-on. Otherwise you get an
elliptically polarized wave. The axial ratio depends on the angle of
incidence and, if the reflector isn't perfectly conducting, on the
impedance of the surface.

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!

I think you mean that polarization (not 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.

That is, in fact, the definition of circular or elliptical polarization.

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

It's the only one which fits the definition. If you choose to rotate the
polarization at some other rate, you should call it something else.

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!

Sorry, it doesn't. An unavoidable side effect of the synchronicity
change is that the amplitude of the E field still changes at a 1 GHz
rate, going through a complete cycle from max to zero to max to zero to
max each nanosecond. A circularly polarized wave doesn't change
amplitude with time. A non-circular elliptical wave changes amplitude
but not fully to zero each cycle.

Circularly polarized waves have many characteristics and particular
relationships to linearly polarized waves. The waves you're producing
don't have some of these characteristics, like the constant amplitude.
Your method doesn't produce circularly polarized waves even though the
polarization does indeed change with time.

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?

Because a circularly polarized antenna responds equally well to all
orientations of linear polarization, the normal helix wouldn't be aware
of the polarization rotation -- unless the polarization rotation was
fast enough to be nearly synchronous.

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

No.

What?

Thoughts, comments?

Sorry, I didn't find it "mind-blowing".

-- Pete K1PO
-- Indialantic By-the-Sea, FL

Roy Lewallen, W7EL

Circular polarization... does it have to be synchronous??
 

"Peter O. Brackett" wrote in message
...

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?

the same as for a linearly polarized wave. since the rotation frequency is
much lower than the carrier frequency (unless you are considering elf
transmissions) during any time period consisting of several cycles of the
carrier it would appear stationary to the antenna.


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


it wouldn't matter. now if there were two linearly polarized antennas
rotating such that their polarizations stayed in sync that would at least
reduce the fading caused by one rotating and the other being stationary.
but only if the path between them didn't produce any rotation or
randomization of the polarization, so essentially only for short paths with
no reflective multi-path or other effects. seems like more trouble than its
worth... what would you gain from it anyway?

Circular polarization... does it have to be synchronous??
 

Roy:

Thanks for your well thought out responses.

See my comments below interspersed with snippings of your response.

[snip]
"Roy Lewallen" wrote in message
treetonline...
Peter O. Brackett wrote:
. . .
It is commonly understood that polarization of electromagnetic waves may
be either linear or circular.

Then some education is in order. Electromagnetic waves are elliptically
polarized. The two extreme special cases of this are linear and circular
(with axial ratio of zero -- or infinite depending on your choice of
definition -- and one respectively). There are an infinite number of other
possible elliptical polarizations with different axial ratios.
[snip]

I agree. My statement was not quite precise.

I should have stated something like, "it is commonly understood that
polarization of waves may be categorized as being either linear or
elliptical, and
in the elliptical category the special case of circular polarization occurs
whenever
the major and minor axes of the elliptical polarization are equal."

[snip]
Of course linear polarization can have any orientation, not just vertical
or horizontal. And even those terms lose meaning when away from the Earth.
However, it's often convenient to mathematically separate waves into two
superposed components of horizontal and vertical polarization.
[snip]

Agreed!

[snip]
The polarization of the dipole signal will be purely horizontal only
directly broadside. The signal off the ends are purely vertically
polarized, and in other directions neither horizontal nor vertical.
[snip]

Agreed! It is relatively difficult, and perhaps even impossible to arrange
the physical configuration of an antenna such that it emits (or receives)
wave of purely one category of polarization.

In practice though many antennas concentrate a major part of their emissions
in one polariztion form.

[snip]
By "mixed" polarization, I assume you mean a single polarization which is
neither horizontal nor vertical and can be described as a "mixture" of a
purely horizontal and a purely vertical wave.
[snip]

No. What I meant by "mixed" was that, just as with daylight for example,
the field contains many polarization orientations. In fact usually outside
in daylight most of the light we see with our eyes contains very nearly
an equal distribution of all polariztions. An exception in the sky's light
is perpedicular to the suns rays where because of upper atmospheric
conditions light becomes slightly polarized. It is claimed that some people
can actually "see" this polarized light differently than normal light.
(Haider's
Brush) Of course many people know that reflected light, for example
from the surface of a lake, becomes highly polarized. This is the
reason that "Polaroid" sunglasses are used by sportsmen and others
to reduce perceived glare from reflective surfaces.

That said, mixed polarization, is also largely the case of HF waves
received over ionospheric paths. In other words HF waves received
over long distances will contain a wide distribution of linear
and perhaps circular polarizations. Thus rendering the use of single
polarized antennas relatively useless at HF by amateurs. Unless of
course one is prepared to pay the significant price in space and
equipment to implement a polarization diversity receiving system.

[snip]
It's also difficult to get the polarizations of the antennas exactly
right.
[snip]

Agreed!

[snip]
There's no advantage at HF of having the antenna orientations the same if
the path is via the ionosphere.
[snip]

True for a single antenna and receiver, which is the usual case for a ham,
see my remarks above.

However if one is willing to pay the price for several antennas and
synchronous
receiving systems then receiving gains can often be obtained by the
exploitation
of polarization diversity.

[snip]
Interesting. Can you work an example for us? I'm curious as to what you
use for theta in the "law's" equation.
[snip]

Theta is just the relative orientation of the polarization of the
transmitting
and receiving antennas, or in the case of an optical polarimeter, the
relative orientations of the polarizing and analyzing polarizer.

Theta is commonly illustrated in undergraduate optical laboratories and
science
experiment kits, using a couple of pieces of "Polaroid" film with the
polarization
angle marked on the film by a notch or other marking. When the
two films are aligned with their polariztion direction perpendicular there
is no
light propagation, i.e. theta is 90 degrees, and when they are aligned with
theta
equal to zero then light is propagated.

In the case of dipole antennas, theta is zero when two antennas are
co-linear and theta is 90 degrees when the antennas are perpendicular.

[snip]
Only if it strikes the surface directly head-on. Otherwise you get an
elliptically polarized wave. The axial ratio depends on the angle of
incidence and, if the reflector isn't perfectly conducting, on the
impedance of the surface.
[snip]

Agreed!

A very intersting optical phenomena to observe is to look at a mirror
through
an optical circular polarizer (polarizer in tandem with a 1/4 wave retarder)
which
renders the "image" of the circular polarizer to be black. i.e. the optical
circular polarizer eliminates the reflection. This technique is widely used
to eliminate reflections from information displays that must operate in high
sunlight with good sunlight readability. High quality high transmissivity
optical circular polarizers are relatively expensive, and so one does not
find such technology applied to consumer displays like computer
monitors, TV sets or IPhones, however optical circular polarizers are
widely used by the military for eliminating sunlight reflections from their
(expensive) information displays.

[snip]
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!

I think you mean that polarization (not frequency) diversity doubles
channel capacity.
[snip]

Yep that's exactly what I meant, but my fingers did not type it that way.
Thanks!

[snip]
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.

That is, in fact, the definition of circular or elliptical polarization.
[snip]

Agreed, both you and I and thousands of others know that. [smile]

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

It's the only one which fits the definition. If you choose to rotate the
polarization at some other rate, you should call it something else.
[snip]

Definition! Gosh where is Cecil when you need him? The only
problem with definitions is that there are so many of them!

---------------------------------------------------------------------------------------------

"When I use a word, Humpty Dumpty said in a rather scornful tone,

"It means just what I chose it to mean - neither more nor less."

"The question is," said Alice, "whether you can make words mean so many
different things."

"The question is," said Humpty Dumpty, "which is to be Master - that's all."

-- Lewis Caroll, from Through the Looking Glass

--------------------------------------------------------------------------------------------

[grin]

[snip]
Sorry, it doesn't. An unavoidable side effect of the synchronicity change
is that the amplitude of the E field still changes at a 1 GHz rate, going
through a complete cycle from max to zero to max to zero to max each
nanosecond. A circularly polarized wave doesn't change amplitude with
time. A non-circular elliptical wave changes amplitude but not fully to
zero each cycle.
[snip]

Here there is a bit of fuzziness...

I agree that the E field of a wave is always changing at the RF carrier
frequency
since it is an AC waveform. Alternating current is always changing! And so
a
1 GHz carrier will always have an E field that oscillates back and forth at
the
carrier (center?) frequency when analyzed by a (linear) polarimeter.

I disagree with you that a circular polarized wave has a constant E field.

Even in the case of a purely circularly polarized the E field still
oscillates
at the carrier (center?) frequency when analyzed by a linear polarizer.

i.e. if a purely CP wave is received on a linear polarized antenna the
detected E field (Volts per meter) will be observed to be oscillating
at the carrier frequency. However if received on a purely CP responding
antenna this oscillating E fileld will appear to be constant.

The E field vector can be considered to be similar to the image of a
spoke on a rolling wheel. The radius of the spoke is constant, but
it's projection on the ground over which the wheel is rolling will
always be oscillating in length.

[snip]
Circularly polarized waves have many characteristics and particular
relationships to linearly polarized waves. The waves you're producing
don't have some of these characteristics, like the constant amplitude.
Your method doesn't produce circularly polarized waves even though the
polarization does indeed change with time.
[snip]

I beg to disagree. The waves that I am describing are exactly the same.

Consider if the mechanical motor that spins my linear antenna spins at
exactly the carrier frequency. There would be then no way to tell the
difference between the two.

[snip]
Because a circularly polarized antenna responds equally well to all
orientations of linear polarization, the normal helix wouldn't be aware of
the polarization rotation -- unless the polarization rotation was fast
enough to be nearly synchronous.
[snip]

Heh, heh... what would you consider to be "fast enough"?

Would the rate of spin have to be 99-44/100 percent of the synchronous
frequency? Or would it have to be closer than that?

At what magic spin frequency would the two be indistinguisable.

FWIW... I can propose a scheme that will electronically rotate the linear
antenna
at any desired frequency, at least up to the accuracy of modern atomic clock
standards.

[snip]
Sorry, I didn't find it "mind-blowing".
[snip]

Roy, I don't belive you have thought about it hard enough yet, for clearly
this idea
has already "blown" your mind!

For did you not state above that a circular carrier wave has a constant
amplitude?

A radio wave with constant aplitude, indeed! Something must be blown!

At zero frequency, how would a constant wave propagate?

This assumption/view that zero frequency wave can propagate is akin to
Cecil's
view that there are no reflections at DC.

I don't mean to be facitious and I am quite serious about all of this.

Just because no one has ever considered non-synchronous circular polariztion
before
does not mean that it doesn't exist, or that it may not be useful.

Me? I have already thought of several potential uses for non-synchronous
circular
polarization. How about polariztion frequency modulation? Or... how about
polariztion phase modulation? Or...

Got you thinking yet?

Thanks again for your clearly interesting comments and feedback.

More thoughts, comments?

-- Pete K1PO
-- Indialantic By-the-Sea, FL

Circular polarization... does it have to be synchronous??
 

Dave:

[snip]
it wouldn't matter. now if there were two linearly polarized antennas
rotating such that their polarizations stayed in sync that would at least
reduce the fading caused by one rotating and the other being stationary.
but only if the path between them didn't produce any rotation or
randomization of the polarization, so essentially only for short paths
with no reflective multi-path or other effects. seems like more trouble
than its worth... what would you gain from it anyway?
[snip]

A better understanding of circular polarization?

The design of a new polariztion locked loop, akin to a phase locked loop,
but...

More?
..
..
..

Thanks!

-- Pete K1PO
-- Indialantic By-the-Sea, FL

Circular polarization... does it have to be synchronous??
 

On Dec 6, 10:11*am, "Peter O. Brackett"
wrote:
Roy:

Thanks for your well thought out responses.

See my comments below interspersed with snippings of your response.

[snip]"Roy Lewallen" wrote in message

treetonline... Peter O.. Brackett wrote:
. . .
It is commonly understood that polarization of electromagnetic waves may
be either linear or circular.

Then some education is in order. Electromagnetic waves are elliptically
polarized. The two extreme special cases of this are linear and circular
(with axial ratio of zero -- or infinite depending on your choice of
definition -- and one respectively). There are an infinite number of other
possible elliptical polarizations with different axial ratios.

[snip]

I agree. *My statement was not quite precise.

I should have stated something like, "it is commonly understood that
polarization of waves may be categorized as being either linear or
elliptical, and
in the elliptical category the special case of circular polarization occurs
whenever
the major and minor axes of the elliptical polarization are equal."

[snip] Of course linear polarization can have any orientation, not just vertical
or horizontal. And even those terms lose meaning when away from the Earth.
However, it's often convenient to mathematically separate waves into two
superposed components of horizontal and vertical polarization.

[snip]

Agreed!

[snip] The polarization of the dipole signal will be purely horizontal only
directly broadside. The signal off the ends are purely vertically
polarized, and in other directions neither horizontal nor vertical.

[snip]

Agreed! *It is relatively difficult, and perhaps even impossible to arrange
the physical configuration of an antenna such that it emits (or receives)
wave of purely one category of polarization.

In practice though many antennas concentrate a major part of their emissions
in one polariztion form.

[snip] By "mixed" polarization, I assume you mean a single polarization which is
neither horizontal nor vertical and can be described as a "mixture" of a
purely horizontal and a purely vertical wave.

[snip]

No. *What I meant by "mixed" was that, just as with daylight for example,
the field contains many polarization orientations. *In fact usually outside
in daylight most of the light we see with our eyes contains very nearly
an equal distribution of all polariztions. *An exception in the sky's light
is perpedicular to *the suns rays where because of upper atmospheric
conditions light becomes slightly polarized. *It is claimed that some people
can actually "see" this polarized light differently than normal light.
(Haider's
Brush) *Of course many people know that reflected light, for example
from the surface of a lake, becomes highly polarized. *This is the
reason that "Polaroid" sunglasses are used by sportsmen and others
to reduce perceived glare from reflective surfaces.

That said, mixed polarization, is also largely the case of HF waves
received over ionospheric paths. *In other words HF waves received
over long distances will contain a wide distribution of linear
and perhaps circular polarizations. *Thus rendering the use of single
polarized antennas relatively useless at HF by amateurs. *Unless of
course one is prepared to pay the significant price in space and
equipment to implement a polarization diversity receiving system.

[snip] It's also difficult to get the polarizations of the antennas exactly
right.

[snip]

Agreed!

[snip] There's no advantage at HF of having the antenna orientations the same if
the path is via the ionosphere.

[snip]

True for a single antenna and receiver, which is the usual case for a ham,
see my remarks above.

However if one is willing to pay the price for several antennas and
synchronous
receiving systems then receiving gains can often be obtained by the
exploitation
of polarization diversity.

*[snip] Interesting. Can you work an example for us? I'm curious as to what you
use for theta in the "law's" equation.

[snip]

Theta is just the relative orientation of the polarization of the
transmitting
and receiving antennas, or in the case of an optical polarimeter, the
relative orientations of the polarizing and analyzing polarizer.

Theta is commonly illustrated in undergraduate optical laboratories and
science
experiment kits, using a couple of pieces of *"Polaroid" film with the
polarization
angle marked on the film by a notch or other marking. *When the
two films are aligned with their polariztion direction perpendicular there
is no
light propagation, i.e. theta is 90 degrees, and when they are aligned with
theta
equal to zero then light is propagated.

In the case of dipole antennas, theta is zero when two antennas are
co-linear and theta is 90 degrees when the antennas are perpendicular.

[snip] Only if it strikes the surface directly head-on. Otherwise you get an
elliptically polarized wave. The axial ratio depends on the angle of
incidence and, if the reflector isn't perfectly conducting, on the
impedance of the surface.

[snip]

Agreed!

A very intersting optical phenomena to observe is to look at a mirror
through
an optical circular polarizer (polarizer in tandem with a 1/4 wave retarder)
which
renders the "image" of the circular polarizer to be black. *i.e. the optical
circular polarizer eliminates the reflection. *This technique is widely used
to eliminate reflections from information displays that must operate in high
sunlight with good sunlight readability. *High quality high transmissivity
optical circular polarizers are relatively expensive, and so one does not
find such technology applied to consumer displays like computer
monitors, TV sets or IPhones, however optical circular polarizers are
widely used by the military for eliminating sunlight reflections from their
(expensive) information displays.

[snip] 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!

I think you mean that polarization (not frequency) diversity doubles
channel capacity.

[snip]

Yep that's exactly what I meant, but my fingers did not type it that way.
Thanks!

[snip] 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.

That is, in fact, the definition of circular or elliptical polarization..

[snip]

Agreed, both you and I and thousands of others know that. *[smile]

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

It's the only one which fits the definition. If you choose to rotate the
polarization at some other rate, you should call it something else.

[snip]

Definition! *Gosh where is Cecil when you need him? *The only
problem with definitions is that there are so many of them!

---------------------------------------------------------------------------------------------

"When I use a word, Humpty Dumpty said in a rather scornful tone,

"It means just what I chose it to mean - neither more nor less."

"The question is," said Alice, "whether you can make words mean so many
different things."

"The question is," said Humpty Dumpty, "which is to be Master - that's all."

* * * * * * * * *-- Lewis Caroll, from Through the Looking Glass

--------------------------------------------------------------------------------------------

[grin]

[snip] Sorry, it doesn't. An unavoidable side effect of the synchronicity change
is that the amplitude of the E field still changes at a 1 GHz rate, going
through a complete cycle from max to zero to max to zero to max each
nanosecond. A circularly polarized wave doesn't change amplitude with
time. A non-circular elliptical wave changes amplitude but not fully to
zero each cycle.

[snip]

Here there is a bit of fuzziness...

I agree that the E field of a wave is always changing at the RF carrier
frequency
since it is an AC waveform. *Alternating current is always changing! *And so
a
1 GHz carrier will always have an E field that oscillates back and forth at
the
carrier (center?) frequency when analyzed by a (linear) polarimeter.

I disagree with you that a circular polarized wave has a constant E field..

Even in the case of a purely circularly polarized the E field still
oscillates
at the carrier (center?) frequency when analyzed by a linear polarizer.

i.e. if a purely CP wave is received on a linear polarized antenna the
detected E field (Volts per meter) will be observed to be oscillating
at the carrier frequency. *However if received on a purely CP responding
antenna this oscillating E fileld will appear to be constant.

The E field vector can be considered to be similar to the image of a
spoke on a rolling wheel. *The radius of the spoke is constant, but
it's projection on the ground over which the wheel is rolling will
always be oscillating in length.

[snip] Circularly polarized waves have many characteristics and particular
relationships to linearly polarized waves. The waves you're producing
don't have some of these characteristics, like the constant amplitude.
Your method doesn't produce circularly polarized waves even though the
polarization does indeed change with time.

[snip]

I beg to disagree. *The waves that I am describing are exactly the same..

Consider if the mechanical motor that spins my linear antenna spins at
exactly the ...

read more »



It was stated above that the purely horizontal polarisation will occur
when the dipole is broadside
This is not correct
Using an optimiser and inserting a one liner where all dimensions are
different allows for the design to conform to Maxwell
laws in their entirety, which means the inclusion of the "weak" force
required for equilibrium
Regards
Art

Circular polarization... does it have to be synchronous??
 

"Art Unwin" wrote in message
...
the inclusion of the "weak" force
required for equilibrium

leave it up to art to take a perfectly good premise and insert utter idiocy
into it. next he'll be saying that since the magical levitating weak force
neutrinos are jumping off the antenna at an angle to the element that the
polarization is caused by them. how about it art, can you make your
levitating neutrinos rotate in different directions with left or right hand
circular antennas??

Circular polarization... does it have to be synchronous??
 

On Dec 6, 10:37*am, "Dave" wrote:
"Art Unwin" wrote in message

...

the inclusion of the "weak" force
required for equilibrium

leave it up to art to take a perfectly good premise and insert utter idiocy
into it. *next he'll be saying that since the magical levitating weak force
neutrinos are jumping off the antenna at an angle to the element that the
polarization is caused by them. *how about it art, can you make your
levitating neutrinos rotate in different directions with left or right hand
circular antennas??

You can have diversity with respect to all polarizations except
circular
where you only have the choice of one. If you believe that antenna
programs
are utter idiocy then that will be inline with your general attitude.
I am sure that some have taken up my suggestion to check for
themselves
instead of resorting to knee jerk reactions with out foundation.
One more fool like you on this newsgroup changes little
Art

Circular polarization... does it have to be synchronous??
 

"Art Unwin" wrote in message
...
You can have diversity with respect to all polarizations except
circular where you only have the choice of one.

why can't you do lhcp and rhcp diversity?

If you believe that antenna programs
are utter idiocy then that will be inline with your general attitude.
I am sure that some have taken up my suggestion to check for
themselves instead of resorting to knee jerk reactions with out foundation.

on the contrary, i believe antenna programs and understand how they work, at
one time i wrote one of my own that did well on designing phased vertical
arrays... and not a single reference to the weak force in it at all! nor
will you find any of the existing antenna modeling programs that use the
weak force. which kind of contradicts your whole rant, you say you believe
in the modeling programs and that they give results that agree with your
corrupted weak force model, and yet they don't use the weak force at all...
never have, and never will. nor can you state where the weak force is
included in Maxwell's equations, which of course all the modeling programs
are based on. so that just leaves you hanging by your magical equilibrium
levitating diamagnetic neutrinos... which you still haven't explained how
they work with my ferromagnetic radiators.

Circular polarization... does it have to be synchronous??
 

On Sat, 06 Dec 2008 18:46:16 GMT, "Dave" wrote the
lamentations of a weak mind struggling with the high concepts of an
infinitely Byzantine theory from the laboratories of Ærthur:

on the contrary, i believe antenna programs and understand how they work, at
one time i wrote one of my own that did well on designing phased vertical
arrays... and not a single reference to the weak force in it at all!

It is singularly impossible for them to have not included the weak
force - whose total contribution to the resulting -um- results
registers in the 13th digit to the right of the decimal point.
Dismissing this immense revelation is like arguing that a drowning man
is immune from the effects of a drunk ****ing into the ocean.

nor
will you find any of the existing antenna modeling programs that use the
weak force.

op. cit.

which kind of contradicts your whole rant,

That well may be seeing that Ærthur practices a self reinforcing
argument that exhibits that quality of Æquilibrium: damned if you do,
and damned if you do it again.

you say you believe
in the modeling programs and that they give results that agree with your
corrupted weak force model,

A corrupted weak force, the wæk force?

and yet they don't use the weak force at all...

Of course they do (op. cit.)

never have, and never will.

Always has and always will (I already said that didn't I? (which is
what op. cit. mæns in Lat.))

nor can you state where the weak force is
included in Maxwell's equations,

Ærthur, while rooting in the library stacks of an ancient university
located on the banks of a great (but not grand) lake, he discovered
them in the margins (long neglected as flyspecks on the page due to
their singular characteristic out 13 places to the right). Patents
are pænding, so watch your step.

As we are taxpayers, supporting inventors on the dole, it should be
our full right to be able to examine these hidden documents, but
Ærthur continues to suppress their access.

which of course all the modeling programs
are based on. so that just leaves you hanging by your magical equilibrium
levitating diamagnetic neutrinos... which you still haven't explained how
they work with my ferromagnetic radiators.

The only thing he hasn't explained is the beneficial prosperities of
the color of the color-coded wire. Just as all resistors look the
same except for the colors - and we are all perfectly aware that not
all resistors are the same - hence it is a color thing. (Lest we
diverge into the side topic of wæk resistance, aka Unpedance.)

73's
Richard Clark, KB7QHC