Stealth and active cancellation

[AeroFranz]

Since I found no real thread on this, i thought I'd start one on active radar cancellation.
I heard rumors (very sketchy) about B-2 having a lot of antenna real estate in the leading edges that could be used towards this goal. Certainly advances in computing power and active arrays could be a big help, but I think the task is daunting to say the least. Not being an EM expert myself, I would be interested in hearing the member's opinion on this, namely

1) is this within the state of the art? how would you use it (in selected directions only, say, to cancel the main leading edge/ trailing edge spikes?)
2) do bi-static radars invalidate any attempts at cancellation?
3) which platforms (if any) are/will be equipped with this technology?

Thanks!

 

[gery]

hi aerofranz,

Stealth technogie has been.....today with "portable telephone relais antenna" (that you can see on top of block and house) you can detect all "flying think" by triangulation....all relais create a "static radar"
Only subdevelopped countrys can dread "shadow plane's"...

 

[AeroFranz]

Yes, I've heard speculation about that, but just speculation. I have not read reliable accounts of how well that works. I can see maybe some usefulness as a surveillance device, but I doubt that something of the sort would give you a firing solution. More like "there's something out there in that general direction".

 

[overscan (PaulMM)]

Yup, its been speculated, but I've not heard of anyone even trying it as a test let alone putting such a system into operation.

 

[gery]

Hi over scan,

Like we tel in "FRANCE" ......"No smock without fire"....pas de fumée sans feu....

France developped a news static radar called "NOSTRADAMUS"...it' send "low frequency" microwaves in direction of stratosphere...all "flying think" in middle of heart and startosphere is detected..
Just type in web...for more infos...

Stealth technology is very old....developped by german' in WW2 with Ho 229 "ferrite paint" and ply wood covered (plus the fist realy designed stealth shape....) for plane...and the " indetectable u boot" covered with
a "caoutchouc fine holed" cover called "alberich" see here..

http://www.uboataces.com/sonar-coating.shtml

Northrop studied captured Horten plane like Ho 6 (hi perf glider ) for his performances....and the Ho 229 for his advansed technology...they made many year after the B2..

Today, you can see at NASM the Horten glider restaured and the Only one first stealth plane the Ho 229...

 

[AeroFranz]

There are two Horten gliders hanging in the Steven F. Udvar-Hazy Smithsonian annex at Dulles, DC. The Ho-IX (Go-229) is so far unrestored at the Garber facility, malheureusement closed to public.
Regarding the -229's supposed stealth qualities, there should be a national geographic documentary coming out this year with RCS tests performed by Northrop Grumman - see appropriate thread(s) in this forum.

Returning to radar detection, I hadn't heard of Nostradamus, I will have to check it out and see if I find a description of how it works. i might be wrong, but within the constraints of antenna size and power available, wouldn't you be able to produce the phase conjugate of any incoming frequency?
BTW, It's not quite active cancellation, but i heard that AESA radars can modify returning radiation in such a way that the detection radar "thinks" the aircraft is actually in a different location ("ghost returns"). Anyone care to comment?

 

[Jemiba]

There was an article about jamming in AirInternational 11/1999, describing what you probably meant.
The method is called "range deception jamming". The jammer increases the delay between the echo
and the stronger jamming signal, so on the radar screen the distance of the tagret seems to inrease.
(diagram from the mentioned AI)

 

[gery]

aerofranz,
can you tel where i can see the famous article...
"national geographic documentary coming out this year with RCS tests performed by Northrop Grumman"..please..

Just an interesting detail about Ho IV b (first picture...) you can note that the profil of the root's wing is'nt the "horten standart profil" (airframe) but an "experimental profil" developped by german's ingeniors inspired (copied) from a captured "Mustang" for this exeptionnal low drag coef...

 

[gery]

some infos about "nostradamus"..sorry in french...

http://www.lexpansion.com/economie/nostradamus-le-radar-ultralucide-peut-voir-les-avions-furtifs_16931.html
http://www.onera.fr/synindex/radar-nostradamus.html
http://www.techno-science.net/?onglet=articles&article=32&page=8
http://www.onera.fr/images-science/installation-experience/nostradamus.php
http://gdr-isis.org/rilk/gdr/Kiosque/TheseHDR-351
http://adsabs.harvard.edu/abs/1992ONERA....U....S
http://bbs.keyhole.com/ubb/ubbthreads.php?ubb=showflat&Number=1208234
http://www.bulletins-electroniques.com/actualites/38019.htm

 

[AeroFranz]

can you tel where i can see the famous article...
"national geographic documentary coming out this year with RCS tests performed by Northrop Grumman"..please..

There is at least one thread talking about it http://www.secretprojects.co.uk/forum/index.php/topic,5851.0/highlight,horten+northrop.html

some infos about "nostradamus"..sorry in french...

Thanks for the links, et t'en fais pas, ca ira meme en francais!

 

[gery]

Thank for link...

 

[r16]

regarding range increasing deception , ı believe U-2s carried such means in their flights of Soviet Union .

 

[Spring]

Interesting, so you are saying the B-2 could use destructive interference to reduce it RCS....well..

Welcome to ECM basics

Is a bit funny how the "stealth" technology is promoted, suddenly destructive interference is a stealth concept, suddenly ECM is a bad word which is replaced better with the "EW suits" one

BTW, you can't really hide something with such means, you must know where is each photon to cancel it, which is impossible, not because computer procesing,but because nature laws.

The RCS reduction is nice to avoid missile interception and a good support with ECM, but to penetrate heavy defences, better to use your B-2's terrain following radar, than to rely on "stealth"

The antennas are more likely RWR receivers linked with an automatic pilot

I think the Ho 229 design was purely aerodynamic and had nothing to do with any "stealthy" requirement, for example, one could confuse the engine's placement as somehing that was designed to hide it IR signature, but then...which IR missile was on service in 1945?...

Such kind of confusion stll happens...even in today's aircraft

 

[r16]

without taking sides in any probable argument , the Mosquito has been promoted as an early Stealth type due wooden construction but the only book ı have on stealth says the engines and every single item inside would be visible to the radar due that same wooden structure

 

[cluttonfred]

without taking sides in any probable argument , the Mosquito has been promoted as an early Stealth type due wooden construction but the only book ı have on stealth says the engines and every single item inside would be visible to the radar due that same wooden structure

True, but given the very primitive state of radar at the time, it seems logical that the wooden structure/metal engine and equipment of the Mosquito would have returned a significantly smaller ping than the metal structure, engines and equipment of other aircraft. That ought to decrease the range before the radar operator could make an accurate identification of a target.

 

[r16]

can't argue . ı am repeating what the author said .

 

[Matej]

MBDA-France has been developing active stealth systems that attempt to cancel the radar return from an airframe by transmitting a second signal of equal frequency and amplitude to the genuine return. Unlike Ram, this technique retains is effectiveness at low and medium frequencies, where the efficiency of passive stealth technology tends to decline.

In 1999, the company conducted ground tests using a C-22 target drone fitted with an experimental active-stealth system, and flight tests conducted using ‘testbeds’ (probably C-22s) were carried out at the Centre d’Essais des Landes range at Biscarosse in southwest France.

Possible applications for active stealth measures include the nose, seeker, wing-leading edges and engine air inlets of future missiles. France hopes to use such technology on the mid-life update of the Scalp EG air-to-surface cruise missile, and in next-generation supersonic missiles. Studies have been underway since the mid-1990s, when designers investigated a possible stealthy variant of the Apache with a redesigned fuselage of flattened triangular cross-section.

http://www.armadainternational.com/03-4/article-full.cfm

 

[saintkatanalegacy]

would this mean that SPECTRA would come with active cancellation? or does it really have one?

 

[sferrin]

Wouldn't the transmissions from the system themselves be detectable?

 

[saintkatanalegacy]

since they are emissions themselves, they would be. from what i understand, the emissions would just try to spoof the radar into "thinking" that there's nothing there as if it was just background noise.

http://www.geocities.com/capecanaveral/9735/rafale1.htm

 

[donnage99]

The reason why there's a buzz over it is that it supposedly jam "stealthily." However, I'm curious that whether it still carry other fundamental limitation of jamming? What if the enemy are using AESA that emitting random frequency that are virtually impossible to jam? Or that the jammer power is less than the radar scattering of the target?

 

[saintkatanalegacy]

that's the only drawback i guess since the system works only if the enemy radar is sending out consistent frequencies. the problem however is that the enemy radar is giving off its position. but i guess that's where plasma stealth comes in

 

[overscan (PaulMM)]

Cancellation works by transmitting a copy of the incoming radar signal half a wavelength out of phase with the original. With DRFM and very fast processors, it has become more achievable. Done correctly, the two waves cancel each other out and there are no emissions to detect. This is the same principle used in noise-cancelling headphones.

Its not simple to do, but in principle could provide a black box "cloaking device".

 

[Jemiba]

"Wouldn't the transmissions from the system themselves be detectable?"

Following the pure and simple theory, I think not . As the jammer would be
active only when receiving a radar signal, both signals should be wiped out.
With regards to reality, things might be different. Quite probably no aircraft,
not even the stealthiest ones, act as a single Hertzian dipole, but as a conglo-
merate of dipoles, scattered around the aircrafts volume. And every single dipole
would create a different phase shift, then the others, so the returning radar signal
should consist a multitude phase shifts, probably distributed along a Gaussian bell
curve. For an already stealthy aircraft, this curve should be relatively narrow, as
the dipoles, leading and trailing edges, are aligned, although still spatially divided.
But for a non-stealthy aircraft the curve can well be wide enough, to render cancellation
of just a single phase shift useless, I think.

 

[overscan (PaulMM)]

Thats why its taken until now to have the computing power needed to analyse the incoming signal, correctly model the required counter signal and then near-instantaneously transmit it.

 

[Matej]

Note that the original text says, that this technology is going to be applied to the *missiles*. It means relatively simple surface and only a few edges to care about. Also active stealth is usually the supplemental technology, combined with the shape, RAM material, flight profile and other things.

 

[donnage99]

the problem however is that the enemy radar is giving off its position.

What do you mean? That applies for everyone, including your own aircraft, too, right?

but i guess that's where plasma stealth comes in

plasma stealth only works at certain altitude and speed, and from certain angles where it is applied.

 

[zen]

I reccal reading in Flight International BAE Systems wheree looking at this I think.

In theory if enough of the planes skin is covered by this the system can use electric switching of areas on and off to create false impressions of the aircrafts size, shape and even direction of travel and speed.

 

[PNorwood]

Missiles with active-cancellation stealth technology? Now that's a formidable weapon.

 

[saintkatanalegacy]

specially since you can't tell which direction it's heading :-[

what's threatening is that automated protections systems can get fooled

 

[PNorwood]

With active cancellation, I take it you could use any airframe shape and get by

 

[sublight]

Cancellation works by transmitting a copy of the incoming radar signal half a wavelength out of phase with the original. With DRFM and very fast processors, it has become more achievable. Done correctly, the two waves cancel each other out and there are no emissions to detect. This is the same principle used in noise-cancelling headphones.

Its not simple to do, but in principle could provide a black box "cloaking device".

This is technically not correct. For example, if I have a radio that is tuned to receive on 50Mhz and I have 6 devices in the room transmitting at 50 Mhz at the same time they are supposedly "jamming" each other and the radio cannot discern their transmissions. However, these radio waves are not actually canceling each other out, the waveforms all co-exist without interfering with each other at all. The radio just isn't intelligent enough to receive and separate all of their signals at the same time.

Likewise it is the same for radar waves.

What is really happening there is that the receiver is just getting jammed by the inversely phased radiation, while the waves and particles themselves continue on unmolested.

 

[zen]

Well you need a airframe that can fit the systems, and one that is very precisely known in terms of its radar return signature.

 

[saintkatanalegacy]

since it's unlikely to "replicate" pseudorandom frequency, the airframe as well would be needing some RCS reduction as implemented in the rafale(not sure if they really placed the device)

 

[quellish]

1) is this within the state of the art? how would you use it (in selected directions only, say, to cancel the main leading edge/ trailing edge spikes?)
2) do bi-static radars invalidate any attempts at cancellation?
3) which platforms (if any) are/will be equipped with this technology?

Thanks!

1. A likely use is to use it to address sculpted return spikes. VLO designs are all about *managing* the energy the system takes in and reflects back. Because of the limitations of absorbers, etc. and the practical requirements of your aircraft, this means some areas will have high returns - spikes - by design. High is realtive, on a VLO aircraft this is not a lot of energy - which is why it is *possible* to conceal these spikes using an active cancellation system. Concealing a whole conventional aircraft this way would require many antennas, and far too much transmit power to be practical.
2. ....maybe?
3. Something with an already low RCS, that can carry an antenna of the appropriate size, and has the kW to power it. I do not know of a specific platform this could be applied to (other than one from the past), but those requirements would mean things like small missiles would be unlikely. 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.

 

[quellish]

This is technically not correct. For example, if I have a radio that is tuned to receive on 50Mhz and I have 6 devices in the room transmitting at 50 Mhz at the same time they are supposedly "jamming" each other and the radio cannot discern their transmissions. However, these radio waves are not actually canceling each other out, the waveforms all co-exist without interfering with each other at all. The radio just isn't intelligent enough to receive and separate all of their signals at the same time.

Likewise it is the same for radar waves.

What is really happening there is that the receiver is just getting jammed by the inversely phased radiation, while the waves and particles themselves continue on unmolested.

Errrr, no. Overscan is correct.
"Active cancellation involves the process of modifying and retransmitting the received radar signal. The target must emit radiation in the same time with the received pulse whose amplitude and phase cancel the reflected energy. The required data are the angle of arrival, intensity, waveform and frequency of the received wave. An active cancellation system should sense these data accurately and then reradiate the pulse with proper amplitude and phase. Obviously, this requires a challenging task for the system, as the frequency increases the work becomes much more difficult."
...yadda yadda.

 

[sublight]

FYI phase cancellation happens at the receiving antenna and not with the electromagnetic radiation itself. With the right antenna and signal analyzer you would know your getting played.

 

[sublight]

Phase cancellation happens at the receiving antenna and not with the electromagnetic radiation itself.

 

[Jemiba]

I think physically we are speaking of "destructive interference" and
as far as I know, that happens directly to the reflected radiation.

 

[overscan (PaulMM)]

Yes, that is my 'A level' physics understanding too.