How to Counter BVR Missiles- DRFM

[Dr sim]

The AIM-120 AMRAAM. Primary weapon for F22, F35, F15, F16 and F18.

aim-120c.jpg (image)

First some background.
There are three types of air-to-air missile guidance techniques:
• Semi-Active Homing.
• Active Homing.
• Passive Homing.

Semi-Active Homing Guidance:
semiactive.jpg (image)

Missile relies on an external pointed energy source to 'illuminate' the target. The energy reflected by this target is intercepted by a receiver on the missile. The weapon uses radio energy collected by its radar receiver to determine target trajectory and adjust control surfaces/nozzles to intercept.

The American AIM-7 Sparrow and British SkyFlash use this is homing technique.
Active Homing Guidance:
aim-120c.jpg (image)










Active homing works like semi-active homing, except that tracking energy is both transmitted-received by the missile itself. No external source is needed. It is this reason that active homing missiles are called "fire-and-forget".
At longer ranges, called Beyond Visual Range (BVR), these weapons store target information downloaded internally from the launch aircraft - just prior to launch - however can also receive target position updates from launch platform via command-data link (mid course update) data pulse(s) after weopon release. In this BVR mode, the seeker head goes 'active’ (awakens) only for the final terminal phase - close to target. The AIM-54, AIM-120 and Vampel R-77 use this 'fire-and-forget' homing technique. Again most modern active homing air-to-air missiles that operate in the radio (radar) spectrum can delineate a noise-jamming signal (from the target) from their own targeting transmission, and so (can) switch to home-on-jamming, coming off a target.

Passive Homing Guidance:


passive.jpg (image)




Passive missiles instead rely on some form of energy that is transmitted or emitted by the target. Weopon only receives signals and cannot transmit. This includes short range heat-seeking Infrared (IR) class like American AIM-9 Sidewinder and Russian Vympel R-27 the medium range Vympel R-77T, and radio homing ‘anti-radiation’ missiles like AGM-88 HARM in the SEAD (Suppression of Enemy Air Defense) role - used against SAM radar systems.


Although anti-radiation typically is used against fixed enemy radar sites, other types of radio transmissions, including communication radios can also be targeted in this manner.

- Now enter DRFM Jamming -


Digital Radio Frequency Memory (DRFM) is an electronic method for digitally capturing and retransmitting (reproducing) an RF signal. The DRFM technique ‘snoops’ then digitizes the received signals, stores it in memory, then if needed, replicates and retransmits.


phase-shift.bmp (image)




Because it’s a copy of the original signal, the attacking transmitting radar will not be able to distinguish its legitimate original return signal from the DRFM ‘copy’. Neither does DRFM generate and transmit radio 'noise' class jamming, so the ‘home-on-noise-jamming' used by current weopons - is useless.
The real twist with DRFM, is that slight variations in frequency (phase) can be retransmitted (imbedded) by the more powerful DRFM jam signal, to create Doppler (velocity) error in the attackers receiver (seeker) head.
The attacking weapon may not (or can not) resolve these more powerful “false” DRFM signals (in time) - remember - only a fraction of a second of confusion is all that's required - the weapon will fly wide of the target – and so - is defeated.


Su-27M: note wingtips pods. Pods reportedly can “receive” as well as “transmit.”



These type of DRFM signal reproduction could include snooping/creating/retransmitting distorted phase signals to confuse attacking aircraft main radar sets (including radar gun-sights) as well?


Core issues for DRFM may be:
• Any radio-spectrum transmission can be snooped including: beeps, squawks, data-links and digitized radio communications.
• DRFM would not be effective in the Infrared (IR) EM spectrum.
• DRFM increases need for robust Within Visual Range (WVR) capability.
• DRFM may require offering aircrews more than one type of homing technique for BVR, similar to say Vympel R-77 plus Vympel R-77T usage model?


DFRM is used on new aircraft entering service, as well as being able to be fitted to existing legacy platforms (F-15, F-16, F-18) via pods.



This could be one reason that stealth is effectively absent on Grippen, Typhoon and Rafael?


http://http://1.bp.blogspot.com/_aYAUsn-hXgc/SlZnzG1gp7I/AAAAAAAAAEo/qdmTXD0NJk0/s1600-h/alq_903.jpg

Ultra-long range air-breathing weapons, with fully passive wide-band EM-spectrum homing (anti-radiation class) seeker-heads might be the few options remaining for BVR?

LPI (Low Probability of Intercept) radars might give a new lease-on-life to traditional semi-active guidance techniques?

However if DFRM has indeed turned the radio spectrum of the battlefield upside down, then (even) gun-sights using IRST rather than radar - might soon be essential?

 

[gambit]

DRFM tactics can be defeated here...

http://www.defence.pk/forums/477228-post54.html

 

[SQ8]

DRFM tactics can be defeated here...

http://www.defence.pk/forums/477228-post54.html

Know DSP's in my sleep and its freakishly difficult to make them do real time stuff even with GhZ processors for an intensive signal reproduction process. Let alone picoseconds..

 

[zagahaga]

Lol I'll say it once more all ya need to do is 40 degreese down and pu chaff out that how you break a lock

 

[SQ8]

Lol I'll say it once more all ya need to do is 40 degreese down and pu chaff out that how you break a lock

And pause the game if your mother calls you..

 

[Crypto]

And pause the game if your mother calls you..

hahahahahah

 

[hataf]

Lol I'll say it once more all ya need to do is 40 degreese down and pu chaff out that how you break a lock

And pause the game if your mother calls you..

yes normally we do that in games

and i really want to know about reality ....

this video is already posted where Iraqi pilot Doug missiles. he is using the same tactics

look onward to 7:12

 

[vizier]

Many use towed decoys these days to misguide active+homeonjam missiles like this example of israel

X-Guard - New Towed Active RF Decoy

For imaging infrared seekers a red/white phosphorus hot smoke screen might be useful which are used to block FLIR. In aircraft case I don't know how by a uav screening the aircraft flying underneath or something else.

if you can jam the communication signal when the missile ie. amraam is near you(you don't need to detect the signal as you see the missile by irst you can employ wideband comm jamming) by a towed decoy the launching aircraft can't guide the missile for a hit as well.

 

[Nishan_101]

To counter the latest generation of BVRs as well as WVRs missiles which aren't deflected by the Chaff's or Flare's easily, can only and only be countered through Jamming like using the ECM/ECCM/EW countermeasure systems that are fitted in the aircraft. And only those aircraft will and can survive in the battle that are fitted with best EW/ECCM systems

 

[SQ8]

yes normally we do that in games

and i really want to know about reality ....

this video is already posted where Iraqi pilot Doug missiles. he is using the same tactics

YouTube - Dogfights - Dogfights of Desert Storm (2 of 5)

look onward to 7:12

Against a 3rd gen heatseeker..combined with flares and against the hot desert sand.. yes it might work..
Against a monopulse armed 5th gen radar guided missile, with extensive ECCM and home on jam. he is a toasted duck.
If by any chance the eagle driver was armed with an Aim-120.. the Iragi pilot might have been down way before that.
Still.. the iraqi pilot in this case was well trained in combat.

 

[zagahaga]

You can do it with anymissel now a days you need EW suits but it still workIve been taught this when I WAS in CAF but thAt story is for another Tyme

 

[Nishan_101]

You can do it with anymissel now a days you need EW suits but it still workIve been taught this when I WAS in CAF but thAt story is for another Tyme

Whats that CAF mean????

 

[Super Falcon]

well how sam system these days reply to the jammers can they be jammed these days

 

[gambit]

First...We need to have the correct understanding of what is 'digital radio frequency memory' (DRFM) technology...

Digital radio frequency memory - Wikipedia, the free encyclopedia

Digital Radio Frequency Memory (DRFM) is an electronic method for digitally capturing and retransmitting RF signal. DRFMs are typically used in radar jamming, although applications in cellular communications are becoming more common.

DRFM is essentially a replicator/relay technique for over-the-air (OTA) transmissions. The system take in a signal, analyze, amplify and transmit a replica signal. The 'digital' aspect of the technique is what make it superior, just as much of modern technology are 'digital' in operation. DRFM is NOT a technology developed specifically for warfare. But since this is about the military, we will focus on that application.

Second...We need to have a review on radar detection, specifically the 'pulsed' operation of the radar transmission side.

The vast majority of radar systems out there are mono-static, meaning a single antenna perform both transmit and receive functions. In order to detect the echoes that a target may produce from the transmission side, the system must periodically be 'silent' or non-transmitting. The result is a 'pulsed' or 'pulsing' system. A series of pulses is called appropriately called a 'pulse train'. A series of pulse trains make up a transmission, which can be one second or one hour in duration, however capable is the system. So to keep it simple, we will just use the word 'transmission'.

Inside a transmission are four major basic and important characteristics...

- Pulse width
- Pulse frequency
- Pulse amplitude
- Pulse interval

Frequency and amplitude are self explanatory. Pulse width is the duration of a particular pulse. The 'pulse repetition freq' (PRF) is how many pulses per time unit. The PRF is not the operating frequency of the pulse itself. This is a crucial distinction. Interval is the space between a pulse and its brethens, before and after itself. The 'pulse repetition interval' (PRI) is that space between the BEGINNING of one pulse to the BEGINING of the next pulse, regardless of the pulse width. Or between the END of one pulse to the END of the next pulse. In other words, the PRI is from leading-to-leading or trailing-to-trailing, not trailing-to-leading or leading-to-trailing. A designer cannot use both perspectives in his work, meaning he cannot define the PRI as leading-leading in one processing section and trailing-trailing in another. He must consistently use either leading edge or trailing edge throughout. The pulse width and possibly its variability will destroy his work.

Radar detection is a stochastical process, fanciful phrasing for statistics. If a transmission of ten pulses produced only one return or 'echo', it is statistically insignificant. However, we can set the 'alert' threshold to be this low if we want. The 'alert' threshold is when the system display a 'blip' on the scope. The system is basically saying that there is a 'valid' target based upon this one echo out of ten pulses. Another system that has a higher threshold wil dismiss this single echo. May be it is programmed or hard wired to say 'valid' or to 'alert' with two echoes out of ten pulses. What the human operator does with that information is a different issue but for military purposes, any so-called 'valid' target warrant an investigation -- voice or visual. For military purposes, the default assumption is 'hostile' for all so-called 'valid' targets. Guilty until proven innocent and the burden of proof of innocence is upon the target. We can see then that even for civilian air traffic controllers, two echoes out of ten pulses as 'valid' would make for a very busy day asking electronic ghosts for indentifications. For military purposes, fuel cost alone in chasing after said ghosts would bankrupt the air force. So we raise the threshold to be five or more echoes out of ten pulses as 'valid'. At least 50% is reasonable enough.

Enter ECM via DRFM...

The above is the most basic DRFM architecture for whatever purposes. Everything between the converters, analog (ADC) or digital (DAC), gains increasing importance as we move inward, from either end, into the architecture. Signal acquisition can be with a simple blade antenna but not everyone have equal access to the latest processor, which is downstream of the antenna. Anyway...What the system must do is gain an understanding of the transmission's pulse characteristics in order to replicate the transmission to the highest possible fidelity or to create not only a new but different signal for its own transmission. This is where processor power and memory capacity gains that increasing importance. The system's purpose is to create a deceptor signal so it must know as much as possible the details of the transmission. Just like how detection and alert cannot be as simple as one echo out of ten pulses, this DRFM system cannot assume pulse characteristics based upon analyzing just one pulse in that ten. That mean there is a delay between reception and transmission.

These 4 items will affect the overall performance of an ECM system using the DRFM method...

- Processor speed
- Memory (capacity and speed)
- Sampling rate
- Bus speed

Assume that the system can create an effective deceptor signal after analyzing 3 pulses out of 10. The goal then is to transmit that deceptor signal as soon as possible. But if bus speed cannot move that deceptor signal to the transmit section by the time the threat transmission complete its impact, the threat radar may have 8 echoes out of 10 pulses, enough to establish some target resolution. Low memory capacity affect sampling rate and will produce the same effect. Remember, the threat radar will not create a 'valid' target based upon one echo out of ten pulses, therefore, the ideal situation is to deduce threat transmission characteristics from analyzing just one pulse, create a deceptor signal and transmit that BEFORE receiving the second pulse in the threat transmission. Perfect processor, instant speed memory modules or zero impedance circuit board copper trace lines are not possible.

What if the threat radar is frequency agile? What if the threat radar is capable of altering its pulse repetition freq (PRF)? What if the threat radar is capable of altering ALL transmission characteristics, from pulse train to pulse train? That mean the threat radar usually will have some target resolutions before a pulse train is deceived precisely because of that delay in the DRFM process. For this threat radar, itself is not deceived but a particular pulse train is deceived. It mean the threat radar will assume that the first few pulses in a pulse train will be successful before the rest is analyzed by the defender and a DRFM-ed deceptor signal is created. The threat radar will transmit a ten-pulse pulse train and will ignore any echo produced by the last five because it will assume those last five are compromised. Next...The threat radar will produce another ten-pulse pulse train but with a higher pulse amplitude. The next ten-pulse pulse train may have a longer pulse width. The next ten-pulse pulse train may have a shorter PRF. Or a longer PRF. The next ten-pulse pulse train may have a different pulse width. This is why a designer must be consistent on how he define the pulse repetition interval (PRI) as mentioned several paragraphs above. The combinations are enormous and the time constraint created by a missile traveling at double-digit Mach will not allow the defender much time to analyze and attempt to deceive.

So is it possible to deceive a threat radar via DRFM? Absolutely. Is it possible for a threat radar to successfully counter the DRFM method? Absolutely. The issue for both sides is always -- money.

 

[Chogy]

In addition to Gambit's excellent post, always remember that the same engineers who created advanced missiles like the AIM-120 are highly motivated to make that missile as effective as possible, and that includes investing time and resources into internal counter-countermeasures to defeat external jamming, spoofing, and systems like this one ^^^. These are undoubtedly highly classified, but rest assured that they exist.

There's nothing new in this "game." It has been going on for decades in various forms, the most recognizable one being the battle between tanks (armor) and AT weapons. Like a game of tennis, the ball gets knocked back and forth, with one side having an advantage, then the other.