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Stealthy 'dual-CP' emissions (more TV channels)
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. |
"J. Harvey" wrote in message om... Any comments or technical objections? if this were that obvious to you, and it would work as described, it would already be in wide use. i haven't had enough caffeine yet to explain why, but somehow i think you would get complete cancellation and there would be no propagation at all. |
On Sat, 17 Jul 2004 12:11:22 -0000, "Dave" wrote:
"J. Harvey" wrote in message . com... Any comments or technical objections? if this were that obvious to you, and it would work as described, it would already be in wide use. So let's save some federal money by shutting down the USPTO. Everything useful that works has already been thought of, so there's no need for them any more. i haven't had enough caffeine yet to explain why, but somehow i think you would get complete cancellation and there would be no propagation at all. |
good idea, they are just another way for lawyers to make money. any new
idea gets ripped off as soon as its out anyway with cheap imitations... and then lawyers make more money suing the infringers if they can get a hand on them. wrote in message ... On Sat, 17 Jul 2004 12:11:22 -0000, "Dave" wrote: "J. Harvey" wrote in message . com... Any comments or technical objections? if this were that obvious to you, and it would work as described, it would already be in wide use. So let's save some federal money by shutting down the USPTO. Everything useful that works has already been thought of, so there's no need for them any more. i haven't had enough caffeine yet to explain why, but somehow i think you would get complete cancellation and there would be no propagation at all. |
On Sat, 17 Jul 2004 18:11:39 -0000, "Dave" wrote:
good idea, they are just another way for lawyers to make money. any new idea gets ripped off as soon as its out anyway with cheap imitations... and then lawyers make more money suing the infringers if they can get a hand on them. wrote in message .. . On Sat, 17 Jul 2004 12:11:22 -0000, "Dave" wrote: "J. Harvey" wrote in message . com... Any comments or technical objections? if this were that obvious to you, and it would work as described, it would already be in wide use. So let's save some federal money by shutting down the USPTO. Everything useful that works has already been thought of, so there's no need for them any more. i haven't had enough caffeine yet to explain why, but somehow i think you would get complete cancellation and there would be no propagation at all. 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) Walt, W2DU |
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 |
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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 -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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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 |
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 |
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 |
"Walter Maxwell" wrote in message ... On Sat, 17 Jul 2004 18:11:39 -0000, "Dave" wrote: good idea, they are just another way for lawyers to make money. any new idea gets ripped off as soon as its out anyway with cheap imitations... and then lawyers make more money suing the infringers if they can get a hand on them. wrote in message .. . On Sat, 17 Jul 2004 12:11:22 -0000, "Dave" wrote: "J. Harvey" wrote in message . com... Any comments or technical objections? if this were that obvious to you, and it would work as described, it would already be in wide use. So let's save some federal money by shutting down the USPTO. Everything useful that works has already been thought of, so there's no need for them any more. i haven't had enough caffeine yet to explain why, but somehow i think you would get complete cancellation and there would be no propagation at all. 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) Walt, W2DU Walter I'm not bright enough to fully understand all this discussion. But, I wonder if the appropriate phasing of two circularly polarized waves, one RHCP and the other LHCP can result in a linearly polarized wave, not zero. I think I could build an antenna from two crossed dipoles spaced 1/4 wave apart that porduce either RHCP or LHCP radiation depending on how *one* of the dipoles is phased with respect to the other. Feed them in phase and get RHCP. Change the phase of either dipole 180 degrees and get LHCP. The "unchanged" dipole in both cases has the same polarization and phase. If (theoretically) two of these antennas were superimposed on each other, only the phase of *one* dipole of each antenna needs to be 'reversed' to produce the 'reversed' (RH or LH) polarized wave. The other dipole of each antenna can be in phase with each other, so the sum is a linear wave. What am I missing?? Jerry |
On Sun, 18 Jul 2004 15:44:09 GMT, "Jerry Martes" 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) Walt, W2DU Walter I'm not bright enough to fully understand all this discussion. But, I wonder if the appropriate phasing of two circularly polarized waves, one RHCP and the other LHCP can result in a linearly polarized wave, not zero. I think I could build an antenna from two crossed dipoles spaced 1/4 wave apart that porduce either RHCP or LHCP radiation depending on how *one* of the dipoles is phased with respect to the other. Feed them in phase and get RHCP. Change the phase of either dipole 180 degrees and get LHCP. The "unchanged" dipole in both cases has the same polarization and phase. If (theoretically) two of these antennas were superimposed on each other, only the phase of *one* dipole of each antenna needs to be 'reversed' to produce the 'reversed' (RH or LH) polarized wave. The other dipole of each antenna can be in phase with each other, so the sum is a linear wave. What am I missing?? Jerry Well, Jerry, your last statements is correct. Apparently you missed Roy's post, where he explained that two equal harmonically related RHCP and LHCP signals reduce to a linearly-polarized wave. I was out of my tree when I came up with the knee-jerk response of no signal. I knew better, but I spoke without having my brain in motion. Happens too often when one gets to my age. Walt |
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 ? ;-) |
J. Harvey wrote:
"Thanks Roy. It now makes perfect sense to me that 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." That`s true according to J.D. Kraus, inventor of the helical antenna. On page 477 of his 1950 book "Antennas": "Elliptical Polarization as Produced by Two Circularly Polarized Waves - When the amplitudes are equal, the resultant wave is linearly polarized (Fig.15-28a)." Best regards, Richard Harrison, KB5WZI |
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