By: Mercurius
- 31st August 2014 at 20:03Permalink- Edited 1st January 1970 at 01:00
It's not so much the resonant effect, it's just that the RAM doesn't work terribly well in the low band below 3GHz.
Given that very little is published about military-grade RAM and RAS, I do not think we can rely too much of the published details of unclassified materials and their limitations. Some of the latter forms of RAM are already designed to operate at 500 MHz and below. A lot of research is being done on more advanced materials.
I don't see any way of effectively jamming it without either telepathy or espionage to steal the frequency swapping algorithm.
No need for crystal balls or James Bond. In practice, the frequency hopper does not have a huge range of frequencies over which to operate. It remains within a predictable percentage of its centre frequency. As I understand it, the solution is to be able to search that band of frequencies at very high speed in order to locate the signal after each hop, and then start jamming it. (I am sure that I have posted this information some months ago.)
I don't know what kind of tech you reffer about but it kind of unlikely that f-22 and f-35 have such technology in them even if they exist because these 2 aircraft was designed a long time ago
I know little more than I have already said - there is evidence that low-observable techniques applicable to VHF exist, and are either operational or about to become operational.
In 1981 the US DoD set up two 'Tiger Teams' tasked with trying to find a possible technology that could counter the F-117 and B-2. At that time, the Soviets operated large numbers of VHF radars, so the potential capability of these against the new US aircraft would have been investigated. They were presumably judged not to represent a significant threat. That would suggest either that low-observable techniques were expected to cover VHF, or that the data from VHF radars was not accurate enough to cue a weapon system such as a SAM or fighter.
New
Posts: 6,983
By: obligatory
- 31st August 2014 at 20:14Permalink- Edited 1st January 1970 at 01:00
VHF civilian accuracy
operations from the U.S. coastline to points 300 nm offshore are characterized by:
•
Minimum en route altitude of 500 feet above sea level or above obstructions.
•
100
-
foot minimum descent altitude to 100 feet in designated areas.
?
Exclusionary means that, with agreed exceptions, aircraft and operators must be approved to fly in designated RSVM
airspace. Examples of agreed
exceptions are humanitarian, maintenance, aircraft delivery, and military flights. Prior to such
flights, operators must coordinate with the appropriate air traffic service.
2
-
8
•
Navigation accuracy sufficient to support 4 nm wide routes (or narrower) with 95 percent confidence.
By: TR1
- 31st August 2014 at 21:02Permalink- Edited 1st January 1970 at 01:00
""Low-band radars like the VHF-band 55Zh6 can see most LO aircraft much easier, yes. Until recently, there wasn't enough acuracy within a low-band radar to make it really mean anything. Now you've got digital VHF-band AESAs like the 55Zh6 that are significantly more capable. Shorter wavelength systems, such as fire control radars, are what the bulk of LO measures are intended to defeat (things like serrated panel edges, faceting, the intake grill of the F-117, etc.). That includes fighter radars, SAM engagement radars, etc. There's only one aircraft capable of defeating both short and long wavelength systems, and that's the B-2. It's big enough to employ LO measures against the much larger VHF-band type wavelengths, and has various LO features tailored to the smaller fire-control wavelengths as well. An F-22, F-35, or T-50 is too small to do anything relevant against a VHF-band system, short of putting a meter thick coating of RAM on the things. Given the number of advanced long-wavelength systems appearing and their ability to interface directly with SAM units, the F-35 is a hilarious waste of time. The T-50, not so much, as the US has never really put much effort into VHF-band systems. You need big-ass transmitters for one, making them unsuitable for airborne or naval use."
By: halloweene
- 31st August 2014 at 22:03Permalink- Edited 1st January 1970 at 01:00
No need for crystal balls or James Bond. In practice, the frequency hopper does not have a huge range of frequencies over which to operate. It remains within a predictable percentage of its centre frequency. As I understand it, the solution is to be able to search that band of frequencies at very high speed in order to locate the signal after each hop, and then start jamming it. (I am sure that I have posted this information some months ago.)
By: mig-31bm
- 31st August 2014 at 22:29Permalink- Edited 1st January 1970 at 01:00
Given the number of advanced long-wavelength systems appearing and their ability to interface directly with SAM units, the F-35 is a hilarious waste of time. The T-50, not so much, as the US has never really put much effort into VHF-band systems. You need big-ass transmitters for one, making them unsuitable for airborne or naval use."
-Sean O'Connor (SOC).
I will have to disagree with this
SPY-1 and THAAD radar seem very good to detect low RCS target, while US don't have many VHF radar, their air defence system are pretty decent ( very powerful radar), another thing is that t-50 likely go in service much latter than f-35, so I won't say either f-35 or T-50 more useless than the other
By: Mercurius
- 1st September 2014 at 10:37Permalink- Edited 1st January 1970 at 01:00
VHF civilian accuracy
operations from the U.S. coastline to points 300 nm offshore are characterized by:
The document being cited refers to navigation aids, not radar.
An F-22, F-35, or T-50 is too small to do anything relevant against a VHF-band system, short of putting a meter thick coating of RAM on the things. Given the number of advanced long-wavelength systems appearing and their ability to interface directly with SAM units, the F-35 is a hilarious waste of time.
I am aware of Mr O'Connor's reputation as a photo analyst, but does that make him any more qualified to speak about low-observable technologies than the rest of us? The fact that he is apparently being quoted as thinking that the F-35 is "a hilarious waste of time" is no more meaningful than similar sentiments by other posters. The idea that forum members are better placed than members of the F-35 community (including the aircraft's developers, users, and customers) to evaluate the aircraft's usability seems unrealistic, to say the least.
By: halloweene
- 1st September 2014 at 11:54Permalink- Edited 1st January 1970 at 01:00
I do not understand what you are trying to say.
DAmn was doing my best in english :(
What i'm traying to say is that radar pulses aren't simply "pings", but short signal with specific polarization etc. These "patterns" are used by radar receiver to identify its own signals way under background noise threashold using correlators. The same way our GPS identifies a 25W signal coming from 20000 Kms. But the number of these "patterns" is limited.
Hope i was clear and didn't say BS translating ;)
New
Posts: 1,760
By: lukos
- 1st September 2014 at 12:11Permalink- Edited 1st January 1970 at 01:00
Given that very little is published about military-grade RAM and RAS, I do not think we can rely too much of the published details of unclassified materials and their limitations. Some of the latter forms of RAM are already designed to operate at 500 MHz and below. A lot of research is being done on more advanced materials.
Well those are my thoughts on why the B-2 is so stealthy despite it's size. It isn't just relying on RAM for wave absorption. The resonant affect people talk about being the cause only causes a fluctuating difference in RCS between 0.25 and 4 times that of optical. It can be either good or bad, so it probably isn't the reason:
RAM may have improved since the F-117 but that's an untested theory. Radars may have improved too, who knows.
No need for crystal balls or James Bond. In practice, the frequency hopper does not have a huge range of frequencies over which to operate. It remains within a predictable percentage of its centre frequency. As I understand it, the solution is to be able to search that band of frequencies at very high speed in order to locate the signal after each hop, and then start jamming it. (I am sure that I have posted this information some months ago.)
Really not that easy. The waveform is coded and the AN/APG-77 is said to hop 1,000 times per second and the energy can be spread over the X-Band spectrum on each hop. You will only really detect a signal by integrating the X-Band over time. The sector that shows a higher cumulative value is the direction of the AESA. Actually establishing what the frequencies and the coding being used are, on a millisecond basis, is something that I'd need evidence of to believe. Most of the processing components on even the very latest fighters are also at least 10 years old. How do you begin to distinguish between background EM and other transmitters and the actual signal of interest on a millisecond basis?
There is this document on AESA jamming but the conclusions aren't confidence inspiring:
By: lukos
- 1st September 2014 at 12:15Permalink- Edited 1st January 1970 at 01:00
DAmn was doing my best in english :(
What i'm traying to say is that radar pulses aren't simply "pings", but short signal with specific polarization etc. These "patterns" are used by radar receiver to identify its own signals way under background noise threashold using correlators. The same way our GPS identifies a 25W signal coming from 20000 Kms. But the number of these "patterns" is limited.
Why would they be limited? As long as the Rx knows the pattern, they are easily detected on their return and so can take on an unlimited number of patterns. For enemy RWRs who don't know the pattern, not so easy.
By: halloweene
- 1st September 2014 at 12:42Permalink- Edited 1st January 1970 at 01:00
Did i say the opposite? RWR have the advantage of stronger signals, Rx to "know" what to search already...
New
Posts: 1,760
By: lukos
- 1st September 2014 at 13:41Permalink- Edited 1st January 1970 at 01:00
Did i say the opposite? RWR have the advantage of stronger signals, Rx to "know" what to search already...
I'm talking about the sending Rx knowing what frequency patterns to look for. An enemy RWR doesn't know this. The problem is that you have to receive the signal to even begin to guess what it is but then it changes, so you're always faced with a delay. At best you can jam the back end of the pattern over that millisecond which won't be effective. The sender will still get their pulse back plus some downstream garbage which is easily ignored because it's downstream. You could try continuously jamming certain frequencies after monitoring usage and making a prediction but this presents the problem of giving you away because, in itself, it can be detected and then the sending radar can just avoid these frequencies and the unpredictable coding won't be there in the jamming waveform either.
The absolute best bet in jamming an AESA may just be to send back your own random AESA signal, rapidly varying, and hope that there's enough overlap with the sender's signal to mess things up.
By: Mercurius
- 1st September 2014 at 18:14Permalink- Edited 1st January 1970 at 01:00
Really not that easy. The waveform is coded and the AN/APG-77 is said to hop 1,000 times per second and the energy can be spread over the X-Band spectrum on each hop. You will only really detect a signal by integrating the X-Band over time.
I never suggested it was easy, just that it was doable.
Cannot comment on the alleged hop rate of the APG-77, but irrespective of pulse length, each pulse is being transmitted at whatever power level the radar requires, so it is going to be strong, on the same bearing as the last one, and within a predictable frequency range.
I do not know what specifically you mean by 'coding' - the word could have several meanings in this context. However, modern digital RF memory (DRFM) can handle whatever form of coding the radar pulses may have received. You do not need to 'establish' the coding that the enemy radar applied to the pulse, just get the DRFM to copy and mimic the pulse.
At best you can jam the back end of the pattern over that millisecond which won't be effective.
Milliseconds are out of the question - think in terms of nanoseconds for locating the pulse and starting to emit your 'doctored' return. That is the speed needed to make sure that you are jamming for most of the duration of the pulse length.
If you had problems in accepting the concept of working in milliseconds, I would imagine that you will find nanoseconds even less credible. But state of the art EW has always been classified, so I doubt there will be much on the internet for you to see as 'evidence'.
By: Phaid
- 1st September 2014 at 18:36Permalink- Edited 1st January 1970 at 01:00
Given the number of advanced long-wavelength systems appearing and their ability to interface directly with SAM units, the F-35 is a hilarious waste of time.
Nobody is going to use a VHF radar for target engagement, so at best the VHF will hand off the target to some shorter-ranged system which is easier to defeat.
The T-50, not so much, as the US has never really put much effort into VHF-band systems. You need big-ass transmitters for one, making them unsuitable for airborne or naval use."
VHF, yes, but the USN for example uses plenty of UHF radars since the E-2D Hawkeye's APY-9 is a UHF set. The J-20, T-50, etc, are no less vulnerable to detection by radars operating at those wavelengths.
Radar systems work by sending out a signal and then listening for its echo off distant objects. Each of these paths, to and from the target, is subject to the inverse square law of propagation. That means that a radar's received energy drops with the fourth power of the distance, which is why radar systems require high powers, often in the megawatt range, to be effective at long range.[1]
The radar signal being sent out is a simple radio signal, and can be received with a simple radio receiver. It is common to use such a receiver in the targets, normally aircraft, to detect radar broadcasts. Unlike the radar unit, which must send the pulse out and then receive its reflection, the target's receiver does not need the reflection and thus the signal drops off only as the square of distance. This means that the receiver is always at an advantage over the radar in terms of range - it will always be able to detect the signal long before the radar can see the target's echo. Since the position of the radar is extremely useful information in an attack on that platform, this means that radars generally must be turned off for lengthy periods if they are subject to attack; this is common on ships, for instance.
Turning that received signal into a useful display is the purpose of the "radar warning receiver" (RWR). Unlike the radar, which knows which direction it is sending its signal, the receiver simply gets a pulse of energy and has to interpret it. Since the radio spectrum is filled with noise, the receiver's signal is integrated over a short period of time, making periodic sources like a radar add up and stand out over the random background. The rough direction can be calculated using a rotating antenna, or similar passive array using phase or amplitude comparison. Typically RWRs store the detected pulses for a short period of time, and compare their broadcast frequency and pulse repetition frequency against a database of known radars. The direction to the source is normally combined with symbology indicating the likely purpose of the radar - airborne early warning, surface to air missile, etc.
This technique is much less useful against AESA radars. Since the AESA (or PESA) can change its frequency with every pulse (except when using doppler filtering), and generally does so using a pseudo-random sequence, integrating over time does not help pull the signal out of the background noise. Moreover, AESA radars may extend the duration of the pulse and lower their peak power. This makes no difference to the total energy reflected by the target but makes the detection of the pulse by an RWR system less likely.[2] Nor does the AESA have any sort of fixed pulse repetition frequency, which can also be varied and thus hide any periodic brightening across the entire spectrum. Older generation RWRs are essentially useless against AESA radars, which is why AESA's are also known as 'low probability of intercept radars. Modern RWRs must be made highly sensitive (small angles and bandwidths for individual antennas, low transmission loss and noise)[2] and add successive pulses through time-frequency processing to achieve useful detection rates.[3]
AESA radars can be much more difficult to detect that they can broadcast continually and still have a very low chance of being detected. This allows such radar systems to generate far more data than traditional radar systems, which can only receive data periodically, greatly improving overall system effectiveness.
i think the best way to jam an AESA radar is just to use power full barrage noise jamming
New
Posts: 1,760
By: lukos
- 2nd September 2014 at 09:24Permalink- Edited 1st January 1970 at 01:00
I never suggested it was easy, just that it was doable.
Is it? Obviously radar makers and ECM people will do their best but since the introduction of AESA, the advantage is definitely with the radar people. If effective jamming was possible and detection easy, stealth would be redundant for air superiority purposes because every fight would end up WVR.
Cannot comment on the alleged hop rate of the APG-77, but irrespective of pulse length, each pulse is being transmitted at whatever power level the radar requires, so it is going to be strong, on the same bearing as the last one, and within a predictable frequency range.
I have no doubt that integrating across the X-Band wrt time will probably detect AESA but that on its own is a significant task. Actually jamming in such a way that pulses are jammed upstream is the hard part. The strength won't be as easily detected as you think, because the power can be split over a pattern across the frequency range, so whilst it adds up to a lot, the individual intensity at any frequency is low and easily mistaken for noise unless you continually add everything together.
I do not know what specifically you mean by 'coding' - the word could have several meanings in this context. However, modern digital RF memory (DRFM) can handle whatever form of coding the radar pulses may have received. You do not need to 'establish' the coding that the enemy radar applied to the pulse, just get the DRFM to copy and mimic the pulse.
The coding isn't constant, it's time varying too and would again require prediction and more advanced ones even implement changes when an attempt at jamming is made or an enemy is detected.
Milliseconds are out of the question - think in terms of nanoseconds for locating the pulse and starting to emit your 'doctored' return. That is the speed needed to make sure that you are jamming for most of the duration of the pulse length.
If you had problems in accepting the concept of working in milliseconds, I would imagine that you will find nanoseconds even less credible. But state of the art EW has always been classified, so I doubt there will be much on the internet for you to see as 'evidence'.
Show me a fighter with a supercomputer on board and I will think nanoseconds. The problem is that at 1GHz, a single clock cycle = 1 nanosecond. One line of code, depending on what language it's in, can take anything from several clock cycles at assembly code level to dozens of clock cycles at higher language levels. That's just one line of code in what must be a very complicated program. Presumably some bits can be done in FPGA but the complexity of actually adding across the X-Band and time to detect a signal and then trying to isolate the signal and then implementing jamming is hugely complicated. Jamming has traditionally been upstream and downstream to provide effectiveness, upstream isn't possible given the nature of AESA, so that limits you to immediate jamming at the very best. All you can really try do with that is cancel the signal, which is an ar5e of a task in itself and depends on the bearing of the emitter, the orientation of your aircraft and probably even crap like the weather, e.g. how much energy will be absorbed on the return path?
The return is also like a fingerprint, even a feint finger print is still a finger print, so unless you get the whole pulse, or pre-empt it, the jamming is likely ineffective.
New
Posts: 1,760
By: lukos
- 2nd September 2014 at 09:39Permalink- Edited 1st January 1970 at 01:00
and add successive pulses through time-frequency processing to achieve useful detection rates.
i think the best way to jam an AESA radar is just to use power full barrage noise jamming
The bit in bold is exactly what I've been saying as regards detection.
The problem with an all out noise biltz is that the frequency pattern added to the noise will still act as a finger print if we're talking about a white noise type approach. If however, you adopt the approach of simply creating an AESA-like barrage and pseudo-randomly bombard frequency patterns across the X-Band spectrum, that might mess around with the response enough to influence range and velocity computation at the other end if you get lucky. The downfall is that a partial fingerprint will still remain, i.e. a set of frequencies at a given spread with coding across that part intact. A well programmed AESA will be a monster to confront with traditional jamming. RF cyber warfare approaches may have some merit though. If you can't fool the system, corrupt the system or hijack it.
By: halloweene
- 2nd September 2014 at 11:05Permalink- Edited 1st January 1970 at 01:00
The problem with an all out noise biltz is that the frequency pattern added to the noise will still act as a finger print if we're talking about a white noise type approach. If however, you adopt the approach of simply creating an AESA-like barrage and pseudo-randomly bombard frequency patterns across the X-Band spectrum, that might mess around with the response enough to influence range and velocity computation at the other end if you get lucky. The downfall is that a partial fingerprint will still remain, i.e. a set of frequencies at a given spread with coding across that part intact. A well programmed AESA will be a monster to confront with traditional jamming. RF cyber warfare approaches may have some merit though. If you can't fool the system, corrupt the system or hijack it.
Point is do you need to permanently jam the radar or simply disrupt the kill chain?
By: snafu352
- 2nd September 2014 at 11:15Permalink- Edited 1st January 1970 at 01:00
At this point it might be worth asking yourself -
"Why did the Russians design PAK-FA to be so maneuverable when conventional logic would suggest they focus more on VLO instead?"
Good question, if uncomfortable for some. The answer in some less thoughtful peoples minds will be US smart, Russians dumb.
Some companion questions:
Why is the F22 manoeuvrable?
Why was it the original intention of the US that the F22 would be built in much larger numbers?
Why is the F35 manufacturing base spread out across so many US States?
What is a hi - lo mix? ;-)
Posts: 1,149
By: Tu22m - 31st August 2014 at 19:29 Permalink - Edited 1st January 1970 at 01:00
The encryption algorithm has nothing to do with password entropy other than being a limiter.
Posts: 1,348
By: Mercurius - 31st August 2014 at 20:03 Permalink - Edited 1st January 1970 at 01:00
Given that very little is published about military-grade RAM and RAS, I do not think we can rely too much of the published details of unclassified materials and their limitations. Some of the latter forms of RAM are already designed to operate at 500 MHz and below. A lot of research is being done on more advanced materials.
No need for crystal balls or James Bond. In practice, the frequency hopper does not have a huge range of frequencies over which to operate. It remains within a predictable percentage of its centre frequency. As I understand it, the solution is to be able to search that band of frequencies at very high speed in order to locate the signal after each hop, and then start jamming it. (I am sure that I have posted this information some months ago.)
I know little more than I have already said - there is evidence that low-observable techniques applicable to VHF exist, and are either operational or about to become operational.
In 1981 the US DoD set up two 'Tiger Teams' tasked with trying to find a possible technology that could counter the F-117 and B-2. At that time, the Soviets operated large numbers of VHF radars, so the potential capability of these against the new US aircraft would have been investigated. They were presumably judged not to represent a significant threat. That would suggest either that low-observable techniques were expected to cover VHF, or that the data from VHF radars was not accurate enough to cue a weapon system such as a SAM or fighter.
Posts: 6,983
By: obligatory - 31st August 2014 at 20:14 Permalink - Edited 1st January 1970 at 01:00
VHF civilian accuracy
operations from the U.S. coastline to points 300 nm offshore are characterized by:
•
Minimum en route altitude of 500 feet above sea level or above obstructions.
•
100
-
foot minimum descent altitude to 100 feet in designated areas.
?
Exclusionary means that, with agreed exceptions, aircraft and operators must be approved to fly in designated RSVM
airspace. Examples of agreed
exceptions are humanitarian, maintenance, aircraft delivery, and military flights. Prior to such
flights, operators must coordinate with the appropriate air traffic service.
2
-
8
•
Navigation accuracy sufficient to support 4 nm wide routes (or narrower) with 95 percent confidence.
http://www.navcen.uscg.gov/pdf/frp/frp2001/FRS2001.pdf
Posts: 9,579
By: TR1 - 31st August 2014 at 21:02 Permalink - Edited 1st January 1970 at 01:00
""Low-band radars like the VHF-band 55Zh6 can see most LO aircraft much easier, yes. Until recently, there wasn't enough acuracy within a low-band radar to make it really mean anything. Now you've got digital VHF-band AESAs like the 55Zh6 that are significantly more capable. Shorter wavelength systems, such as fire control radars, are what the bulk of LO measures are intended to defeat (things like serrated panel edges, faceting, the intake grill of the F-117, etc.). That includes fighter radars, SAM engagement radars, etc. There's only one aircraft capable of defeating both short and long wavelength systems, and that's the B-2. It's big enough to employ LO measures against the much larger VHF-band type wavelengths, and has various LO features tailored to the smaller fire-control wavelengths as well. An F-22, F-35, or T-50 is too small to do anything relevant against a VHF-band system, short of putting a meter thick coating of RAM on the things. Given the number of advanced long-wavelength systems appearing and their ability to interface directly with SAM units, the F-35 is a hilarious waste of time. The T-50, not so much, as the US has never really put much effort into VHF-band systems. You need big-ass transmitters for one, making them unsuitable for airborne or naval use."
-Sean O'Connor (SOC).
Posts: 4,168
By: halloweene - 31st August 2014 at 22:03 Permalink - Edited 1st January 1970 at 01:00
:applause:
That applies also to waveforms.
Posts: 2,014
By: mig-31bm - 31st August 2014 at 22:29 Permalink - Edited 1st January 1970 at 01:00
I will have to disagree with this
SPY-1 and THAAD radar seem very good to detect low RCS target, while US don't have many VHF radar, their air defence system are pretty decent ( very powerful radar), another thing is that t-50 likely go in service much latter than f-35, so I won't say either f-35 or T-50 more useless than the other
Posts: 1,348
By: Mercurius - 1st September 2014 at 10:37 Permalink - Edited 1st January 1970 at 01:00
The document being cited refers to navigation aids, not radar.
I am aware of Mr O'Connor's reputation as a photo analyst, but does that make him any more qualified to speak about low-observable technologies than the rest of us? The fact that he is apparently being quoted as thinking that the F-35 is "a hilarious waste of time" is no more meaningful than similar sentiments by other posters. The idea that forum members are better placed than members of the F-35 community (including the aircraft's developers, users, and customers) to evaluate the aircraft's usability seems unrealistic, to say the least.
I do not understand what you are trying to say.
Posts: 4,168
By: halloweene - 1st September 2014 at 11:54 Permalink - Edited 1st January 1970 at 01:00
DAmn was doing my best in english :(
What i'm traying to say is that radar pulses aren't simply "pings", but short signal with specific polarization etc. These "patterns" are used by radar receiver to identify its own signals way under background noise threashold using correlators. The same way our GPS identifies a 25W signal coming from 20000 Kms. But the number of these "patterns" is limited.
Hope i was clear and didn't say BS translating ;)
Posts: 1,760
By: lukos - 1st September 2014 at 12:11 Permalink - Edited 1st January 1970 at 01:00
Well those are my thoughts on why the B-2 is so stealthy despite it's size. It isn't just relying on RAM for wave absorption. The resonant affect people talk about being the cause only causes a fluctuating difference in RCS between 0.25 and 4 times that of optical. It can be either good or bad, so it probably isn't the reason:
http://www.radartutorial.eu/01.basics/Rayleigh-%20versus%20Mie-Scattering.en.html
RAM may have improved since the F-117 but that's an untested theory. Radars may have improved too, who knows.
Really not that easy. The waveform is coded and the AN/APG-77 is said to hop 1,000 times per second and the energy can be spread over the X-Band spectrum on each hop. You will only really detect a signal by integrating the X-Band over time. The sector that shows a higher cumulative value is the direction of the AESA. Actually establishing what the frequencies and the coding being used are, on a millisecond basis, is something that I'd need evidence of to believe. Most of the processing components on even the very latest fighters are also at least 10 years old. How do you begin to distinguish between background EM and other transmitters and the actual signal of interest on a millisecond basis?
There is this document on AESA jamming but the conclusions aren't confidence inspiring:
http://edocs.nps.edu/npspubs/scholarly/theses/2006/Sep/06Sep_Denk.pdf
Posts: 1,760
By: lukos - 1st September 2014 at 12:15 Permalink - Edited 1st January 1970 at 01:00
Why would they be limited? As long as the Rx knows the pattern, they are easily detected on their return and so can take on an unlimited number of patterns. For enemy RWRs who don't know the pattern, not so easy.
Posts: 4,168
By: halloweene - 1st September 2014 at 12:42 Permalink - Edited 1st January 1970 at 01:00
Did i say the opposite? RWR have the advantage of stronger signals, Rx to "know" what to search already...
Posts: 1,760
By: lukos - 1st September 2014 at 13:41 Permalink - Edited 1st January 1970 at 01:00
I'm talking about the sending Rx knowing what frequency patterns to look for. An enemy RWR doesn't know this. The problem is that you have to receive the signal to even begin to guess what it is but then it changes, so you're always faced with a delay. At best you can jam the back end of the pattern over that millisecond which won't be effective. The sender will still get their pulse back plus some downstream garbage which is easily ignored because it's downstream. You could try continuously jamming certain frequencies after monitoring usage and making a prediction but this presents the problem of giving you away because, in itself, it can be detected and then the sending radar can just avoid these frequencies and the unpredictable coding won't be there in the jamming waveform either.
The absolute best bet in jamming an AESA may just be to send back your own random AESA signal, rapidly varying, and hope that there's enough overlap with the sender's signal to mess things up.
Posts: 1,348
By: Mercurius - 1st September 2014 at 18:14 Permalink - Edited 1st January 1970 at 01:00
I never suggested it was easy, just that it was doable.
Cannot comment on the alleged hop rate of the APG-77, but irrespective of pulse length, each pulse is being transmitted at whatever power level the radar requires, so it is going to be strong, on the same bearing as the last one, and within a predictable frequency range.
I do not know what specifically you mean by 'coding' - the word could have several meanings in this context. However, modern digital RF memory (DRFM) can handle whatever form of coding the radar pulses may have received. You do not need to 'establish' the coding that the enemy radar applied to the pulse, just get the DRFM to copy and mimic the pulse.
Milliseconds are out of the question - think in terms of nanoseconds for locating the pulse and starting to emit your 'doctored' return. That is the speed needed to make sure that you are jamming for most of the duration of the pulse length.
If you had problems in accepting the concept of working in milliseconds, I would imagine that you will find nanoseconds even less credible. But state of the art EW has always been classified, so I doubt there will be much on the internet for you to see as 'evidence'.
Posts: 342
By: Phaid - 1st September 2014 at 18:36 Permalink - Edited 1st January 1970 at 01:00
Nobody is going to use a VHF radar for target engagement, so at best the VHF will hand off the target to some shorter-ranged system which is easier to defeat.
VHF, yes, but the USN for example uses plenty of UHF radars since the E-2D Hawkeye's APY-9 is a UHF set. The J-20, T-50, etc, are no less vulnerable to detection by radars operating at those wavelengths.
Posts: 2,014
By: mig-31bm - 1st September 2014 at 19:14 Permalink - Edited 1st January 1970 at 01:00
here is good paper explaining LPI Radar and ESM radar detection
http://www.scribd.com/mobile/doc/231936174#fullscreen
i think the best way to jam an AESA radar is just to use power full barrage noise jamming
Posts: 1,760
By: lukos - 2nd September 2014 at 09:24 Permalink - Edited 1st January 1970 at 01:00
Is it? Obviously radar makers and ECM people will do their best but since the introduction of AESA, the advantage is definitely with the radar people. If effective jamming was possible and detection easy, stealth would be redundant for air superiority purposes because every fight would end up WVR.
I have no doubt that integrating across the X-Band wrt time will probably detect AESA but that on its own is a significant task. Actually jamming in such a way that pulses are jammed upstream is the hard part. The strength won't be as easily detected as you think, because the power can be split over a pattern across the frequency range, so whilst it adds up to a lot, the individual intensity at any frequency is low and easily mistaken for noise unless you continually add everything together.
The coding isn't constant, it's time varying too and would again require prediction and more advanced ones even implement changes when an attempt at jamming is made or an enemy is detected.
Show me a fighter with a supercomputer on board and I will think nanoseconds. The problem is that at 1GHz, a single clock cycle = 1 nanosecond. One line of code, depending on what language it's in, can take anything from several clock cycles at assembly code level to dozens of clock cycles at higher language levels. That's just one line of code in what must be a very complicated program. Presumably some bits can be done in FPGA but the complexity of actually adding across the X-Band and time to detect a signal and then trying to isolate the signal and then implementing jamming is hugely complicated. Jamming has traditionally been upstream and downstream to provide effectiveness, upstream isn't possible given the nature of AESA, so that limits you to immediate jamming at the very best. All you can really try do with that is cancel the signal, which is an ar5e of a task in itself and depends on the bearing of the emitter, the orientation of your aircraft and probably even crap like the weather, e.g. how much energy will be absorbed on the return path?
The return is also like a fingerprint, even a feint finger print is still a finger print, so unless you get the whole pulse, or pre-empt it, the jamming is likely ineffective.
Posts: 1,760
By: lukos - 2nd September 2014 at 09:39 Permalink - Edited 1st January 1970 at 01:00
The bit in bold is exactly what I've been saying as regards detection.
The problem with an all out noise biltz is that the frequency pattern added to the noise will still act as a finger print if we're talking about a white noise type approach. If however, you adopt the approach of simply creating an AESA-like barrage and pseudo-randomly bombard frequency patterns across the X-Band spectrum, that might mess around with the response enough to influence range and velocity computation at the other end if you get lucky. The downfall is that a partial fingerprint will still remain, i.e. a set of frequencies at a given spread with coding across that part intact. A well programmed AESA will be a monster to confront with traditional jamming. RF cyber warfare approaches may have some merit though. If you can't fool the system, corrupt the system or hijack it.
Posts: 2,163
By: Amiga500 - 2nd September 2014 at 10:44 Permalink - Edited 1st January 1970 at 01:00
At this point it might be worth asking yourself -
"Why did the Russians design PAK-FA to be so maneuverable when conventional logic would suggest they focus more on VLO instead?"
Posts: 4,168
By: halloweene - 2nd September 2014 at 11:05 Permalink - Edited 1st January 1970 at 01:00
Point is do you need to permanently jam the radar or simply disrupt the kill chain?
Posts: 2,248
By: snafu352 - 2nd September 2014 at 11:15 Permalink - Edited 1st January 1970 at 01:00
Good question, if uncomfortable for some. The answer in some less thoughtful peoples minds will be US smart, Russians dumb.
Some companion questions:
Why is the F22 manoeuvrable?
Why was it the original intention of the US that the F22 would be built in much larger numbers?
Why is the F35 manufacturing base spread out across so many US States?
What is a hi - lo mix? ;-)