Stealth and active cancellation

The destructive interference is a phenomenon experienced at the receiver. There is no phase cancellation of the electromagnetic waves during travel. Try canceling out a laser beam with another one at the same frequency, opposite phase, as a proof of concept. The laser is electromagnetic waves the same as radar, but different wavelength. The different wavelength would not negate the proof of concept.
 
I'm absolutely unsure, but relying on my school physics, I would say, that a wave means
that the oscillators along the path of the wave are stimulated to oscillate between their
neutral point and their amplitude. In the case of destructive interference, they are
experiencing two contrary forces, that in the result would leave the oscillator at his neutral
point, if there's a receiver or not. Actually, such an interference should be recognisable, I think,
as the energy applied must be emitted. As warming up of the rope, in the case of the well known
experiment at school and perhaps as warming up of the air along the wave path in the case of
a cancelled out electromagnetic wave ?
Well, to hard for me !
 
Yes, in case of perfect cancellation no receiver would be capable of resolving the deception. However, sublight has a point in that the interference pattern might be highly directional, so the technique could be defeated by multi-static systems (as quellish has alluded to in another thread).

See: http://en.wikipedia.org/wiki/Double-slit_experiment

One of the slits represents the wave reflected off the target, the other plays the role of the active cancellation transmitter. If the receiver finds itself in an area where the condition

abe9b0ad9089b694ca64b819ed85b01d.png


is satisfied, it will not be able to detect a signal - either signal of the two - no matter how sophisticated it is.
 
Trident said:
Yes, in case of perfect cancellation no receiver would be capable of resolving the deception. However, sublight has a point in that the interference pattern might be highly directional, so the technique could be defeated by multi-static systems (as quellish has alluded to in another thread).

See: http://en.wikipedia.org/wiki/Double-slit_experiment

One of the slits represents the wave reflected off the target, the other plays the role of the active cancellation transmitter. If the receiver finds itself in an area where the condition

abe9b0ad9089b694ca64b819ed85b01d.png


is satisfied, it will not be able to detect a signal, no matter how sophisticated it is.
Click to expand...


When the enemy stops transmitting there will be a lag between the time the signal stops and the time the cancellation signal stops. It may be brief but if you pulsed your radar so the cancellation radar was constantly having to do that maybe you could detect the brief periods where only the cancellation signal was transmitting with passive sensors.
 
From what I can gather, active stealth probably works by sending out a mask signal that modifies the return the threat radar detects, rather then eliminating it, and doing so in such a way that the threat hardware logic and clutter rejection software decides the track cannot be an aircraft. That could be accomplished a number of ways, most likely several of the simultaneously. The actual radar return being detected can actually become larger, not smaller depending on how the jamming is implemented. This would all be specific to known threat radars.

Remember that modern radars aren’t displaying waveforms like an oscilloscope anymore, it’s a computer generated video of what the radar program thinks exists. Everything from swarming insects to mountains and the moon is filtered out of the raw return. A big chunk of the worlds radars are physically compromised to France and other NATO states, so a whole lot of options should be possible.

This kind of stealth is also logically subject the same limitations jammers are, you can only output so much power on so many frequencies with so much bandwidth on each one. It might work fairly well against a SAM battery already isolated from its air defense system or a small formation of enemy planes, but not as well in larger scenarios or against a sophisticated enemy with a lot of passive electronic warfare gear.
 
Watch the video. Like I said, interference happens at the antenna. Jamming just got a whole lot harder....

http://www.youtube.com/watch?v=RiQb5NdDWgk
 
Not so fast there, this set-up is about addressing self-interference and conventional jamming, not active cancellation! The system is entirely consistent with my explanation in the other thread, and thus does not invalidate the active cancellation approach. The emissions from each transmit-antenna are coherent and the receive-antenna is placed in a location where destructive interference between them is known to occur, given their separation and phase relationship. This causes the first radio's own transmissions to cancel each other out at that particular place and those from the other radio (which are NOT coherent with respect to the first one) to become legible even while it is emitting simultaneously. A jammer that produces a signal in such a way that it interferes destructively with the emissions from the second radio at the location of the first radio's receive-antenna (the equivalent of using active cancellation against a radar) would shut down communications between the two no problem at all.

What's more, that is actually a good example of how well active cancellation works in theory: think of the signal from the first of the radio's transmit-antennas as the radar return from the target while the other represents the active cancellation emitter. The receiver is unable to detect either the return or or the interfering transmission, as long as the jammer is able to maintain an emission pattern which puts the receiver inside a null area (which it can do by adjusting its cancellation signal appropriately).

Again, you have a point in that another receiver in a different location might be outside the area of cancellation, i. e. a multi-static radar might be able to defeat the technique. If the target knows the whereabouts of the receiver (rather than just operating on the assumption that it is co-located with the transmitter) even that can be taken care of, though. So to have a good chance of detecting the target you'd preferably have two receive-antennas, separated by a significant distance to ensure that it will be difficult for the target to generate an interference pattern which blanks both of them at the same time. You OTOH seem to be under the impression that this video proves how a mono-static radar would be able to deal with active cancellation and that is definitely not the case.

It's also worth remembering that multi-static radar has been touted as a countermeasure to passive stealth as well, so it is not clear whether this vulnerability of active cancellation represents a significant weakness compared to the conventional approach.
 
The professor highlights that the interference is at the antenna, not with the radio waves. I believe this supports the argument that you cannot distort/cancel/etc a radio wave with a radio wave.
 
quellish said:
It may be possible, however, to use an aircraft's existing AESA radar as an active RCS control system, for a limited range of frequencies. Food for thought.
Click to expand...

Yes, that's an interesting idea! Sounds like an ideal complement for a frequency-selective radome.

sublight said:
The professor highlights that the interference is at the antenna, not with the radio waves. I believe this supports the argument that you cannot distort/cancel/etc a radio wave with a radio wave.
Click to expand...

You are way too hung up on the literal meaning of those words, I think (note that he *never* said anything like "not with the radio waves"). Given the transmitter antenna set-up in those radios there would always be destructive interference at the location where they have placed the receiver (and certain other places as well), no matter whether the receive-antenna is actually present or not. The job of an active cancellation system is to make sure that such a null area is created in the same place where the enemy's receiver is.
 
Do you still have the doubts about the active stealth cancellation or about the quiet helicopters?

http://en.store.creative.com/headphones-headsets/ep-3nc/437-19120.aspx
 
Matej said:
Do you still have the doubts about the active stealth cancellation or about the quiet helicopters?

http://en.store.creative.com/headphones-headsets/ep-3nc/437-19120.aspx
Click to expand...

Big difference between a closed, controlled, environment and the wide outdoors. I've yet to see an active cancellation system that would nullify the neighbor's super loud stereo for example.
 
sferrin said:
Big difference between a closed, controlled, environment and the wide outdoors. I've yet to see an active cancellation system that would nullify the neighbor's super loud stereo for example.
Click to expand...

Such things are out there. There are audio equivalents to AESAs, and I've seen/heard demos of them being used for targetted active cancellation. Sadly not quite ready for office use. I had seen something about using such a thing for crowd control though.
 
Not sure where to put this but DOT&E had a gem that rarely gets much open literature coverage.

http://www.dote.osd.mil/pub/reports/FY2017/pdf/other/2017lfte.pdf


In the RF domain, JASP has funded projects to develop
and implement algorithms to detect Digital RF Memory
(DRFM)-based jamming, mitigate DRFM jamming, and
employ DRFM jamming to counter advanced RF threat
weapons systems.
- In FY17, the Naval Research Laboratory (NRL) completed
a multi-year project to develop algorithms that enable a
friendly system to detect hostile DRFM emissions and
then provide an electromagnetic screen for friendly radar
systems to operate freely behind. NRL completed testing
with the ALQ-214 system and published the results.
- In FY17, the Air Force Special Operations Command
completed a 3-year project to develop 12-bit DRFM
techniques against three RF threat systems with
non-traditional signals of interest. The Special Operations
Command has transitioned the first technique into the
ALQ-211(V)2 (utilized by a variety of fixed-wing and
rotorcraft) and is working to add the second and third
techniques to ALQ-211(V)6 & 9 in FY18.
 
Doesn't the Rafale use some sort of active cancellation system? And what about the "Khibini" system that supposedly "shut down" American Aegis destroyers in the Baltic? I'm not saying it did, but they touted it as using a signal processor to send out a return signal to baffle the incoming missile or whatever...

It makes sense, if I was a Russian planner why spend Billions on stealth when you could use Low frequency radars an IR sensors to detect stealth aircraft like bombers and fighters?

It would also make sense to use some sort of active radar cancellation EW system to make the stealth aircraft miss their intended air targets and force them to either run or get into a close range engagement with a conventional aircraft having equal or better aerodynamic performance. If that philosophy could be successfully used by the Russians it would be a huge way to save money for the Russians and keep flying updated Mig-29s, Mig-35s well into the future.

Is this their approach? it seems like they aren't too concerned about the stealth threat. Sure the T-50 has basic stealth shaping but it is very conservative. And restarted the Blackjack bomber fleet, which isn't very stealthy.
 

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