RWR and SARH - How does it work?

[Cmptohocah]

I was wondering for a long time how does the RWR detect launch of a SARH missile. If it detects a change in the radar emission after the missile has been launched: How, and if at all, does it know if the missile is still on the way or it strayed off course and is not a threat anymore? If there are two target aircraft flying in close formation should both of their RWR detect the launch?

 

Thank you for any clarification.

[Scendore]

I'm sure some can answer better than I can but as I remembered it... RWR basically tells you that you're being Illuminated by a radar. It will change tone if that radar locks you because now it's focusing on you. Lastly it can detect a launch because now that weapon is being guided. I'm not sure but I believe the RWR can also detect the missiles own radar. Perhaps it only knows that something was launched at you. In the sim the only way you know you've lost track is when you break the radar lock. Not sure how it works in real life.

[Basher54321]

Basically (as I understand it) at launch the enemy radar will change the signal it sends to Continuous Wave type so it can guide the missile.

 

The enemy radar then must maintain the lock to guide the missile until it hits - so the RWR will keep sensing the CW signal until the missile hits you or the lock is broken for whatever reason.

[Bimbac]

CW illumination is no longer used because of its disadvantages.

 

Given the hardware currently available in DCS, the only cue that SARH missile is (possibly) launched is the STT warning, generated by RWR. Modern systems can detect other footprints, but generally, radar guiding an SARH missile doesn't change the waveform, just generates the M-link for the missile.

[Dudikoff]

Basically (as I understand it) at launch the enemy radar will change the signal it sends to Continuous Wave type so it can guide the missile.

 

AFAIK, the SARH missile seeker guided by CW illumination must be locked before the launch and thus the CW illumination will be started by the WCS I presume when the target is locked and tracked by the radar (and within a certain range depending on the selected missile type, I'd expect) and the missile is selected so that a missile lock can be established. So, for that kind of SARH missiles you cannot detect the launch.

Edited June 12, 2015 by Dudikoff

[GGTharos]

What bimbac wrote is likely the most correct answer. The RWR knows about the launch because the mlink is now transmitted to the missile. There may be other cues as well, I know the F15 does some interesting stuff when launching a sparrow.

[Cmptohocah]

... The RWR knows about the launch because the mlink is now transmitted to the missile....

 

So as long as the launch platform is communicating with the missile, RWR can pick up on that and interpret it as a launch?

 

Does it mean that the target RWR is issuing warnings until the SARH missile self-destructs, goes out of m-link range or that link is for any reason broken?

 

How would the RWR choose or differentiate that that particular link is aimed at the RWR being targeted? Does it use logic like: 1. Am I locked? 2. Is there an m-link? If 1. and 2. are true then issue a launch warning?

 

Thank you for the answers!

[GGTharos]

The warning is issued until the m-link transmission ceases. The missile isn't communicating with the launching radar, so that transmission may continue for some time. And yes the logic would be STT+M-Link.

[Tombstone]

So as long as the launch platform is communicating with the missile, RWR can pick up on that and interpret it as a launch?

Given RWR will have given PI against given m-link, and that will be most likely less than 100%. So its not granted that RWR will be able to pickup and distinguish m-link.

RWR can interpret anything it pickups anyhow it "likes", thing is, if it will be correct interpretation. For example what prevents enemy from transmitting m-link even when not guiding missile?

 

Does it mean that the target RWR is issuing warnings until the SARH missile self-destructs, goes out of m-link range or that link is for any reason broken?

RWR has no idea when missile self destructs, or if there was any real missile launch at all.

 

How would the RWR choose or differentiate that that particular link is aimed at the RWR being targeted? Does it use logic like: 1. Am I locked? 2. Is there an m-link? If 1. and 2. are true then issue a launch warning?

In modern systems that's probably programmable according to EOB. When missile uses m-link its still mid-course so radar can be in TWS mode so there is no lock.

[Basher54321]

AFAIK, the SARH missile seeker guided by CW illumination must be locked before the launch and thus the CW illumination will be started by the WCS I presume when the target is locked and tracked by the radar (and within a certain range depending on the selected missile type, I'd expect) and the missile is selected so that a missile lock can be established. So, for that kind of SARH missiles you cannot detect the launch.

 

Looks correct - would have thought the exact implementation should be dependent on what you can take from the specific radar being picked up.

 

 

Looking at the Nam era AN/APR-26 Launch Warning Receiver regarding SARH SA-2 (slightly different) - that triggered a launch on the signalling change to high PRF from the Fan Song but did not signal an actual launch - only that one was imminent.

 

The kit would measure the intensity of the azimuth and vertical scan signals from the Fan Song radar to determine that it was that aircraft actually under attack - not the wingman.

 

 

There are some good manuals on F-15C radar procedures from the early 80s that show the desired tracking mode is high PRF and the radar would continually attempt to switch to this when tracking a target in AIM-7 (MRM) mode.

There is no indication of any change when the AIM-7 is launched - so again just a switch to high PRF was likely the RWR launch warning trigger.

 

To complicate things further the radar could still launch AIM-7s in a Flood mode if the radar cannot switch to hi PRF (On the other hand SA-2xs could be launched optically or in HOJ in the 60s.)

 

 

I have no info on AIM-7 employment post 1990.

[Tombstone]

@Basher54321: SA-2 is radio-command guided not SARH.

[GGTharos]

The 26 had a pretty complicated way of signalling a launch, and you could get a false positive or a false negative depending on things.

 

It also picked up the M-Link ;)

 

And yes, there is an indication of change when the 7 is launched.

[WildBillKelsoe]

RWR detects frequency changes of radars painting your ship. If a radar guided missile is tracking you, this is a different band. Same for paint, same for lock. Chaff works by creating a larger cross section of you, but to be effective, at least in DCS, you have to sandwich chaff between you and the launcher.

 

There is a SAM simulator that requires one of those old 1024x1280 displays, but it teaches you the basics of SAMs, and its free. My favourite is the SA-2 guideline.

[GGTharos]

Who says that the stuff that applies to old SAMs applies to modern AI radars and AAMs?

[Basher54321]

@Basher54321: SA-2 is radio-command guided not SARH.

 

Yes - but a good example of how the RWR is determining signals from the tracking radar. The Fan Song still has to do all the tracking - it just relays the information to the missile differently.

[Basher54321]

The 26 had a pretty complicated way of signalling a launch, and you could get a false positive or a false negative depending on things.

 

 

You can get a false Positive / Negative on any RWR gear - let alone back then - the inputs don't come with CRC checks unfortunately.

 

Today LPI techniques and AESA would suggest massive issues for basic RWRs - so a change to multisensor/spectrum detection can only be a good thing.

[GGTharos]

What do CRC checks have to do with this?

 

The APR-25 would pick up the missile uplink signal, the various fan-song radar bands and their operating PRF, as well as some other threats in the area.

 

The pilot had to understand what all the indicators meant to judge what was really going on.

 

It really is that simple:

Which band, which PRF, is it steady or not, is the uplink up or not ... the funny thing is that the Fire Cans would provide position for the SA-2 to guide his missile until close, so you'd see AAA radars and an SA-2 uplink, you might think he's trying to fake you out ... then the last 5-10 sec you'd get the E-Band HPRF as the SA-2 operator would now start using the SA2 radar for terminal guidance.

[Basher54321]

Means that mother nature does not always provide clarity in the provided information.

 

Jamming pods and area Jamming also screwed up the RHAW gear a lot.

 

 

The FireCan could apparently relay information to the Fansong the same way as Spoon Rest/Flat Face etc.

In another case you might have been jamming the uplink and get no launch warning at all due to track on Jam techniques.

[ilya1502]

How does the RWR determine the type of the signal source? It differs SA-2 from SA-8 and both of them from Su-27. How does it do that?

 

Also, what is M-link?

[Tombstone]

By signal parameters like carrier frequency, pulse repetition frequency, duty cycle, modulation, etc. It can also analyze combined antenna-scan characteristic, ringing on pulse edges, but that is mostly done in ELINT receivers.

 

M-link is missile link - radio-frequency channel used to transmit guidance/mid-course navigation data to/from missile.

[Dudikoff]

There are some good manuals on F-15C radar procedures from the early 80s that show the desired tracking mode is high PRF and the radar would continually attempt to switch to this when tracking a target in AIM-7 (MRM) mode.

There is no indication of any change when the AIM-7 is launched - so again just a switch to high PRF was likely the RWR launch warning trigger.

 

OK, but I was talking about older missiles which were guided by a separate CW illuminator (so, e.g. up to AIM-7F). The one described here is probably for the 1982 AIM-7M which had a monopulse seeker so basically after it was introduced, the CW illuminator was no longer necessary on the F-15C and was even disabled at some point (there was a comment by GGTharos on the very forum saying when it was disabled, but it was a long time ago), but I guess that depended on how long the AIM-7F was used on the type. For these missiles, all the sources mention that illumination was necessary only in the final stages so I'd expect that an actual seeker lock was not necessary for launch (i.e. a digital autopilot receiving midcourse updates were guiding the missile towards the target until the seeker was in range).

 

I don't know if a switch to High PRF would be used in RWR systems to indicate a possible launch, but, if so, again, it would be more like a "launch imminent" warning (which I believe you were trying to say, but it's not clear from the end comment).

Edited June 13, 2015 by Dudikoff

[ilya1502]

By signal parameters like carrier frequency, pulse repetition frequency, duty cycle, modulation, etc. It can also analyze combined antenna-scan characteristic, ringing on pulse edges, but that is mostly done in ELINT receivers.

I presume this requires a thorough knowledge of the enemy hardware... Does it usually come from spying or are there other ways? Say, analyzing data gathered inflight or something...

Edited June 13, 2015 by ilya1502

[Tombstone]

There are dedicated ELINT platforms to gather this sort of information like RC-135, other than that, data can come from analysis of acquired equipment and of course espionage.

[GGTharos]

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