FYI:
CP = Circular Polarization
RHCP = Right Hand CP
LHCP = Left Hand CP
FYI = For your information ;-)


New concept...?

If one were to arrange for the emission of a RHCP signal, and the same
- but inverted - LHCP signal, then the resultant composite 'dual-CP'
emission should be more-or-less undetectable by any linear antenna.
This is because a linear antenna in any orientation would respond
equally to both circular senses and, since one sense carries the
inverted signal, they'd cancel out (within the linear antenna) to the
degree that balance and symmetry is maintained.

Only an appropriate CP antenna would be able to extract the 'dual-CP'
signal. Obviously - use a more complex 'dual-CP' antenna system to
extract both senses, suitably de-invert one, and then combine at RF
for purposes of improving S/N by +3dB.

Since the RHCP and LHCP senses are inherently isolated from each
other, there doesn't seem to be any reason why such a 'dual-CP' signal
couldn't be easily generated and extracted. The RF hardware
implementation is fairly obvious (nearly trivial).

Also, that such a 'dual-CP' signal would be more-or-less ignored by a
linear antenna also seems obvious.

The most immediately-obvious application is a 'stealthy' transmission,
at least until someone shows up with a bent whip on their receiver.

Interesting, but not that exciting.

Then the penny drops...

This concept could be applied to satellite broadcasting (for example)
to provide ANOTHER (3rd) downlink polarization. In other words, for
FSS satellite (for example) where they already use two linear
polarizations (H and V) to double their effective bandwidth, this
'dual-CP' transmission technique could provide a '3rd axis' (thereby
increasing the total effective bandwidth by another up to +50%).

The satellite example has the huge practical advantage over the
'stealthy' example in that the receiving station is co-operating (if
his antenna is defective, he'll get it fixed). This co-operation would
help to maintain isolation of the 3rd axis.

The isolation won't be perfect for various reasons (for example,
perhaps Faraday rotation through the ionosphere would upset the CP
balance). But the isolation doesn't have to be perfect for the new
axis to provide valuable RF real estate.

The same sort of concept could also be applied at the baseband level
thereby reducing some of the RF hardware while providing the same
benefit on a transponder-by-transponder, narrower bandwidth, basis.
It's an option to further explore anyway.

Any comments or technical objections?

de VE1BLL (Jeff)

PS: The ' e-mail is NOT monitored - respond in group only.

The sum of LHCP and RHCP fields of equal magnitude is a linearly
polarized field. The orientation of that linearly polarized field
depends on the relative phases of the LHCP and RHCP fields.

Roy Lewallen, W7EL

J. Harvey wrote:

FYI:
CP = Circular Polarization
RHCP = Right Hand CP
LHCP = Left Hand CP
FYI = For your information ;-)


New concept...?

If one were to arrange for the emission of a RHCP signal, and the same
- but inverted - LHCP signal, then the resultant composite 'dual-CP'
emission should be more-or-less undetectable by any linear antenna.
This is because a linear antenna in any orientation would respond
equally to both circular senses and, since one sense carries the
inverted signal, they'd cancel out (within the linear antenna) to the
degree that balance and symmetry is maintained.

Only an appropriate CP antenna would be able to extract the 'dual-CP'
signal. Obviously - use a more complex 'dual-CP' antenna system to
extract both senses, suitably de-invert one, and then combine at RF
for purposes of improving S/N by +3dB.

Since the RHCP and LHCP senses are inherently isolated from each
other, there doesn't seem to be any reason why such a 'dual-CP' signal
couldn't be easily generated and extracted. The RF hardware
implementation is fairly obvious (nearly trivial).

Also, that such a 'dual-CP' signal would be more-or-less ignored by a
linear antenna also seems obvious.

The most immediately-obvious application is a 'stealthy' transmission,
at least until someone shows up with a bent whip on their receiver.

Interesting, but not that exciting.

Then the penny drops...

This concept could be applied to satellite broadcasting (for example)
to provide ANOTHER (3rd) downlink polarization. In other words, for
FSS satellite (for example) where they already use two linear
polarizations (H and V) to double their effective bandwidth, this
'dual-CP' transmission technique could provide a '3rd axis' (thereby
increasing the total effective bandwidth by another up to +50%).

The satellite example has the huge practical advantage over the
'stealthy' example in that the receiving station is co-operating (if
his antenna is defective, he'll get it fixed). This co-operation would
help to maintain isolation of the 3rd axis.

The isolation won't be perfect for various reasons (for example,
perhaps Faraday rotation through the ionosphere would upset the CP
balance). But the isolation doesn't have to be perfect for the new
axis to provide valuable RF real estate.

The same sort of concept could also be applied at the baseband level
thereby reducing some of the RF hardware while providing the same
benefit on a transponder-by-transponder, narrower bandwidth, basis.
It's an option to further explore anyway.

Any comments or technical objections?

de VE1BLL (Jeff)

PS: The ' e-mail is NOT monitored - respond in group only.

Roy Lewallen wrote:
The sum of LHCP and RHCP fields of equal magnitude
is a linearly polarized field. The orientation of
that linearly polarized field depends on the
relative phases of the LHCP and RHCP fields.

....and...

Walter Maxwell wrote:
Without giving the problem any serious mathematical
or physical thought, only knee-jerk intuition, IMO,
if a radiator suitable for radiating CP of either
hand were fed with equal signals leading to both
RHCP and LHCP simultaneously, I agree with the
poster above that complete cancelation would result,
and there would be no radiation.
This is why a linearly-polarized antenna could not
receive any energy. (har har)

One of my assumptions is that the RHCP and LHCP can operate in
complete isolation of each other. DBS satellites (for example) use
RHCP and LHCP to double their bandwidth, just like FSS satellites use
H and V. I have not heard anything about the DBS RHCP transponder
having to worry about the LHCP transponder. I haven't heard any
mention of nulls suddenly appearing and disappearing in the downlink
passband as the two senses happen to coincide, out of phase. I haven't
heard about the CP being converted to linear and causing interference
(at -3dB) in the other CP mode.

I assume that the two CP signals have no knowledge of each other. The
hardware can be designed (easily) to maintain that isolation - imagine
the two transmitter hidden from each other and the signals just happen
to be headed in the same direction. In other words - for purposes of
argument - it doesn't have to be the same antenna.

It just so happens that, for this 'dual-CP' concept, the two CP
signals happen to be the same but one is inverted. They don't have to
'know' about their evil mirror-image twin.

If they cancel out, then where does the energy go? Make it a mega-watt
each and follow the smoke. If they combine in the vacuum of space,
where is the smoke?

Appreciate your comments...

de VE1BLL

On 17 Jul 2004 13:27:03 -0700, (J. Harvey) wrote:

Roy Lewallen wrote:
The sum of LHCP and RHCP fields of equal magnitude
is a linearly polarized field. The orientation of
that linearly polarized field depends on the
relative phases of the LHCP and RHCP fields.

...and...

Walter Maxwell wrote:
Without giving the problem any serious mathematical
or physical thought, only knee-jerk intuition, IMO,
if a radiator suitable for radiating CP of either
hand were fed with equal signals leading to both
RHCP and LHCP simultaneously, I agree with the
poster above that complete cancelation would result,
and there would be no radiation.
This is why a linearly-polarized antenna could not
receive any energy. (har har)

One of my assumptions is that the RHCP and LHCP can operate in
complete isolation of each other. DBS satellites (for example) use
RHCP and LHCP to double their bandwidth, just like FSS satellites use
H and V. I have not heard anything about the DBS RHCP transponder
having to worry about the LHCP transponder. I haven't heard any
mention of nulls suddenly appearing and disappearing in the downlink
passband as the two senses happen to coincide, out of phase. I haven't
heard about the CP being converted to linear and causing interference
(at -3dB) in the other CP mode.

I assume that the two CP signals have no knowledge of each other. The
hardware can be designed (easily) to maintain that isolation - imagine
the two transmitter hidden from each other and the signals just happen
to be headed in the same direction. In other words - for purposes of
argument - it doesn't have to be the same antenna.

It just so happens that, for this 'dual-CP' concept, the two CP
signals happen to be the same but one is inverted. They don't have to
'know' about their evil mirror-image twin.

If they cancel out, then where does the energy go? Make it a mega-watt
each and follow the smoke. If they combine in the vacuum of space,
where is the smoke?

Appreciate your comments...

de VE1BLL

Hi Jeff, my age is showing. In my knee-jerk reaction I stupidly thought of
applying the RH and LH sigs from the same source. Of course your concept works
when the signals are supplied from two different sources. The two signals are
totally oblivious to each other.

I know this is true, because it's exactly the method I used in developing the
antennas for TIROS 1, the World's first weather satellite. The circuit concept I
used there comprised a four-port hybrid ring, or rat race. The two transmitters
fed two opposite input ports. Each of the ouput ports fed a two-port balun, each
balun port feeding one terminal of a dipole. However, the line from one of the
output ports had a 1/4wl extra length, and the dipole fed from this output port
was oiented 90° from the other. With this arrangement, the radiation of the
signal entering one input port of the hybrid is inherently RHCP and from the
other is LHCP. The signals from each transmitter were received on a
linearly-polarized antenna at any orientation angle, with no mutual
interference.

If you'd like I can send you a copy of the circuit diagram in jpg format. This
coupling system was fabricated in stripline, so if you'd like, I'll also send
you a copy of that. Actually, the total system comprised the use of four
transmitters, with each pair operating in two different frequency bands. The
total coupling system fed all four transmitters simultaneously into one antenna.

Please let me know if you'd like me to send the stuff.

Walt, W2DU

J. Harvey wrote:

One of my assumptions is that the RHCP and LHCP can operate in
complete isolation of each other. . .

Some time ago, I stated that at any point in space there's a single
field, and that we can split it into various components to suit our
analytical needs. But the way we choose to split it or, conversely, the
way it was created (from a single source or polarization, or multiple
ones) doesn't alter the nature of the field in any way. I'm not sure if
what I said was simply disbelieved or whether it was ignored -- the end
result is the same.

The total field you get from simultaneous RHCP and LHCP waves is simple
to see by using the index finger of each hand to represent the
instantaneous orientation of the E field from each of two waves. Point
the index finger of your left hand downward and the index finger of your
right hand upward, knuckle-to-knuckle, so the fingers make a vertical
line extending from one fingertip to the other. The left index finger
will represent the LHCP wave and the right index finger the RHCP wave.
At the beginning instant that we're illustrating, they're out of phase
and sum to zero. So the field at that point and that time is zero.

Now rotate your left finger 45 degrees CCW and the right finger 45
degrees CW, to represent how the fields are oriented 1/8 period later or
1/8 wavelength away. If you add the two finger "vectors", you find the
result is a field that's horizontal, pointing to the left, and 1.414
times the length of one finger. Rotate the fingers another 45 degrees,
the left finger CCW and the right one CW. Now they're both pointing to
the left, and the sum is a horizontal field with magnitude equal to 2
fingers. If you continue this process, you'll find that the sum of the
two fields is always horizontal, and it oscillates between zero and two
fingers in instantaneous amplitude. It is, in fact, exactly the same as
and entirely indistinguishable from a horizontally polarized wave coming
from, say, a dipole. You can reach the same conclusion mathematically
from the equations I posted a few weeks ago.

If you run the same experiment beginning with the fingers in phase --
both pointing upwards -- you'll get a purely vertically polarized wave.
And with other starting phase angles, you'll get linearly polarized
waves of other orientations.

No magical energy distruction or disappearing takes place -- it's all
accounted for. And you can receive it just fine with a dipole.

Roy Lewallen, W7EL

Roy Lewallen wrote:
If you run the same experiment beginning with the fingers in phase --
both pointing upwards -- you'll get a purely vertically polarized wave.

Actually, I got the same two fingers back on the freeway the other day. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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On Sat, 17 Jul 2004 16:48:38 -0500, Cecil Moore wrote:

Roy Lewallen wrote:
If you run the same experiment beginning with the fingers in phase --
both pointing upwards -- you'll get a purely vertically polarized wave.

Actually, I got the same two fingers back on the freeway the other day. :-)

Cecil, you're lucky you got two back. I usually only get one.

Walt

On Sat, 17 Jul 2004 14:26:54 -0700, Roy Lewallen wrote:

J. Harvey wrote:

One of my assumptions is that the RHCP and LHCP can operate in
complete isolation of each other. . .

Some time ago, I stated that at any point in space there's a single
field, and that we can split it into various components to suit our
analytical needs. But the way we choose to split it or, conversely, the
way it was created (from a single source or polarization, or multiple
ones) doesn't alter the nature of the field in any way. I'm not sure if
what I said was simply disbelieved or whether it was ignored -- the end
result is the same.

The total field you get from simultaneous RHCP and LHCP waves is simple
to see by using the index finger of each hand to represent the
instantaneous orientation of the E field from each of two waves. Point
the index finger of your left hand downward and the index finger of your
right hand upward, knuckle-to-knuckle, so the fingers make a vertical
line extending from one fingertip to the other. The left index finger
will represent the LHCP wave and the right index finger the RHCP wave.
At the beginning instant that we're illustrating, they're out of phase
and sum to zero. So the field at that point and that time is zero.

Now rotate your left finger 45 degrees CCW and the right finger 45
degrees CW, to represent how the fields are oriented 1/8 period later or
1/8 wavelength away. If you add the two finger "vectors", you find the
result is a field that's horizontal, pointing to the left, and 1.414
times the length of one finger. Rotate the fingers another 45 degrees,
the left finger CCW and the right one CW. Now they're both pointing to
the left, and the sum is a horizontal field with magnitude equal to 2
fingers. If you continue this process, you'll find that the sum of the
two fields is always horizontal, and it oscillates between zero and two
fingers in instantaneous amplitude. It is, in fact, exactly the same as
and entirely indistinguishable from a horizontally polarized wave coming
from, say, a dipole. You can reach the same conclusion mathematically
from the equations I posted a few weeks ago.

If you run the same experiment beginning with the fingers in phase --
both pointing upwards -- you'll get a purely vertically polarized wave.
And with other starting phase angles, you'll get linearly polarized
waves of other orientations.

No magical energy distruction or disappearing takes place -- it's all
accounted for. And you can receive it just fine with a dipole.

Roy Lewallen, W7EL

You're absolutely right, Roy, I confess I shot without aiming properly. It's
been many years since I worked with CP, and I now remember going through the
same exercise that you presented above with the same result, a
linearly-polarized wave. Thanks for the refresher course.

Walt, W2DU

Correction:

Roy Lewallen wrote:
. . .
Now rotate your left finger 45 degrees CCW and the right finger 45
degrees CW, to represent how the fields are oriented 1/8 period later or
1/8 wavelength away. If you add the two finger "vectors", you find the
result is a field that's horizontal, pointing to the left, and 1.414
times the length of one finger. Rotate the fingers another 45 degrees,
the left finger CCW and the right one CW. Now they're both pointing to
the left, and the sum is a horizontal field with magnitude equal to 2
fingers. . . .

My rotation was reversed -- it should read:

Now rotate your left finger 45 degrees CCW and the right finger 45
degrees CW, to represent how the fields are oriented 1/8 period later or
1/8 wavelength away. If you add the two finger "vectors", you find the
result is a field that's horizontal, pointing to the *right*, and 1.414
times the length of one finger. Rotate the fingers another 45 degrees,
the left finger CCW and the right one CW. Now they're both pointing to
the *right*, and the sum is a horizontal field with magnitude equal to 2
fingers. . . .

The conclusion isn't affected by the error.

Roy Lewallen, W7EL

Roy Lewallen
...
And you can receive it just
fine with a dipole.

Thanks Roy.

It now makes perfect sense to me that since CP can be generated with
two linear antennas (crossed dipoles, phased appropriately), it must
be true that one could make linear using two CP antennas - just as you
reminded us.

Still - I have a nagging feeling that, taking advantage of the -3dB
separation between CP and linear, there must be at least a small (3dB
SNR) Shannon window in there that might be used to squeeze through
some extra data. Likely not (yet) cost effective even it it does
exist.

I appreciate all the responses.

Now - what shall I do with the $10,000 that I didn't spend on a patent
?

;-)