reported AIM-120C losing targets easily for chaff even at close ranges

[Blinky.ben]

7 hours ago, nighthawk2174 said:

@BIGNEWY @GGTharos

 

Couldn't find much more than this about chaff effectiveness but well its in the .01-.02% range for an older con-scan pulse tracking radar with MTI.  Considering stuff like the amraam is going to have much better resolution, is monopulse, will be closer meaning an even smaller res cell, and is PD.  And that based on other sources the bloom rate for the chaff in the simulation is highly optimistic well...  An additional factor to also consider is that the RCS of the target aircraft is 10, which is reasonable but for the off axis test the rcs of the aircraft was not varied where it would irl where it'd grow significantly as you approached the beam.  And even more so with an increase in look down or up angle on an aircraft.

 

This chart doesn’t help a lot for this specific situation without knowing what was being used. Sam radars are entirely different systems compared to air to air radars. Air to air will always be the inferior cousin to Sam networks. Do we know what system was used for these charts? I would imagine this is ground based information.

 

what was the result they were trying to achieve. Are these results if the radar is now tracking chaff or is it the radar just lost lock on the aircraft?

 

All chaff needs to achieve is to create problems for the radar to deal with and that will always happen. All the examples you have that the radar has as features are all processes that happen AFTER the radar has already done much other processing that the chaff has made the radar go through due to its new presence. Meaning it has had to see the chaff and go through the process to identify it is not the target you want to track and then remove the chaff. So no matter how amazing a radar is chaff will ALWAYS no matter what have some kind of effect no matter the situation and no matter what aspect it just some aspects will have less issue the others. All the features you explained are features to help the radar stop tracking chaff but doesn’t exactly stop the missile losing lock which can happen for a huge amount of reasons before Doppler, speed gates, range gates have even started being a thing, when the missile is tracking the contact the radar pulse is still picking up objects in the area and it still has to process what keeps coming back to the missile while its still tracking a target and even if one pulse comes back too strong or makes the missile miss other pulses or anything that forces the radar to change a setting before Doppler is introduced then a problem has been created and the missile has to deal with that. This is why a lookup aspect is almost one of the greatest advantages you can have (I would argue it is more important then the Doppler feature that is over rated by the community) and look down aspect has such a huge disadvantage and this doesn’t include the problems that notching bring to the table either. But again notching only helps defeat the last part of the overall processing the radar has to go through.

 

Im with BIGNEWY in that I think there is some Hollywood expectations happening by SOME not all. The resistance from the Aim-120 before the change that caused this topic was too resistant, I’m not saying that’s it not broken now either but it definitely should not be how it was before.

Edited March 19, 2021 by Blinky.ben

[SgtPappy]

8 hours ago, nighthawk2174 said:

Couldn't find much more than this about chaff effectiveness but well its in the .01-.02% range for an older con-scan pulse tracking radar with MTI.  Considering stuff like the amraam is going to have much better resolution, is monopulse, will be closer meaning an even smaller res cell, and is PD.  And that based on other sources the bloom rate for the chaff in the simulation is highly optimistic well...  An additional factor to also consider is that the RCS of the target aircraft is 10, which is reasonable but for the off axis test the rcs of the aircraft was not varied where it would irl where it'd grow significantly as you approached the beam.  And even more so with an increase in look down or up angle on an aircraft.

 

 

 

Just a nitpick here, but I think that probability it expressed in decimals - not percent in this graph where probability, P(bl) = 1.0 is 100% probability. It's convention and I don't see why they'd make a graph where the maximum is 1% while showing an asymptotic rise in probability. So P(bl) = 0.01 is 1%. Much larger than 0.01%, but yes your point still stands. It looks like the break lock probability is tiny. I think I may have this very paper somewhere in my files but didn't really look into it since it's about conscan radars. 

 

4 hours ago, TotenDead said:

If we are talking about the radar air defense systems that were in Vietnam, then they were not Doppler. The SNR-75 had an optionally enabled moving target selection mode, which worked on a Doppler, but I see no point in enabling it to destroy aircraft when they are not flying inside a preventively scattered foil cloud

I believe that the leading edge and trailing edge tracking techniques work in non-PD systems. You just cut the start or end of the pulse return so you reject chaff (depending on if the target is leaving or coming toward the radar while dropping chaff). This, I imagine, would significantly decrease SNR to a prohibitive value if applied to the smaller airborne radars in fighters. 

 

2 hours ago, Blinky.ben said:

Im with BIGNEWY in that I think there is some Hollywood expectations happening by SOME not all. The resistance from the Aim-120 before the change that caused this topic was too resistant, I’m not saying that’s it not broken now either but it definitely should not be how it was before.

 

This is tough one, because I'm not confident that anyone can really prove that the AMRAAM was "too resistant" but then again I barely play on modern servers often so I don't know what others have experienced. As Nighthawk mentioned, the advancements in tech could really explain the AMRAAM's chaff resistance. Yes chaff will always have an effect on radar but would you actually be able to spoof AMRAAMs from 3 nm by spamming chaff and beaming? I'm inclined to believe no.

[dundun92]

4 hours ago, Blinky.ben said:

The resistance from the Aim-120 before the change that caused this topic was too resistant [...] it definitely should not be how it was before

And exactly what is the basis for this claim?

[nighthawk2174]

6 hours ago, Blinky.ben said:

This chart doesn’t help a lot for this specific situation without knowing what was being used. Sam radars are entirely different systems compared to air to air radars. Air to air will always be the inferior cousin to Sam networks. Do we know what system was used for these charts? I would imagine this is ground based information.

Not really they are comparable they work of the exact same principles.  Also It was not a specific radar but a generic con-scan FCR with MTI.

 

6 hours ago, Blinky.ben said:

what was the result they were trying to achieve. Are these results if the radar is now tracking chaff or is it the radar just lost lock on the aircraft?

That the radar was dragged onto the chaff and has lost lock of the aircraft.

 

6 hours ago, Blinky.ben said:

All chaff needs to achieve is to create problems for the radar to deal with and that will always happen. All the examples you have that the radar has as features are all processes that happen AFTER the radar has already done much other processing that the chaff has made the radar go through due to its new presence.

Language barrier? not sure what your trying to say here.

6 hours ago, Blinky.ben said:

 Meaning it has had to see the chaff and go through the process to identify it is not the target you want to track and then remove the chaff.

when the missile is tracking the contact the radar pulse is still picking up objects in the area

Well I mean first off if the chaff is not in the resolution cell of the target then it's not going to really do anything.  And it won't stay in the resolution cell for very long at all.  Not to mention it takes time for the chaff to bloom which will negatively impact its effect while it's in the res cell.  Plus with monopulse it has the ability to tell there are multiple targets in its resolution cell to the point it can compensate for this and track on the original target.

6 hours ago, Blinky.ben said:

So no matter how amazing a radar is chaff will ALWAYS no matter what have some kind of effect no matter the situation and no matter what aspect it just some aspects will have less issue the others. 

Sure but is that effect even enough to make a difference?  Based on what i've read I don't really think it has much noticeable impact especially with modern radars.

6 hours ago, Blinky.ben said:

All the features you explained are features to help the radar stop tracking chaff but doesn’t exactly stop the missile losing lock

 

No all of these features are there to reject clutter and keep the target locked.  

6 hours ago, Blinky.ben said:

 and it still has to process what keeps coming back to the missile while its still tracking a target and even if one pulse comes back too strong or makes the missile miss other pulses or anything that forces the radar to change a setting before Doppler is introduced then a problem has been created and the missile has to deal with that. 

Hence why its an integrative (not sure if that's the correct word) proces, it aggregates a bunch of returns over a short time.  And also how would this problem cause an immediate break lock? 

6 hours ago, Blinky.ben said:

This is why a lookup aspect is almost one of the greatest advantages you can have (I would argue it is more important then the Doppler feature that is over rated by the community) and look down aspect has such a huge disadvantage and this doesn’t include the problems that notching bring to the table either. But again notching only helps defeat the last part of the overall processing the radar has to go through.

I don't think that doppler processing is at all overrated plus it doesn't work alone either there are other mechanisms that support each other.

6 hours ago, Blinky.ben said:

Im with BIGNEWY in that I think there is some Hollywood expectations happening by SOME not all. The resistance from the Aim-120 before the change that caused this topic was too resistant, I’m not saying that’s it not broken now either but it definitely should not be how it was before.

 

I completely disagree how it was before was far more representative imho based on all of the various papers that i've linked in this thread.

[Blinky.ben]

8 hours ago, dundun92 said:

And exactly what is the basis for this claim?

18 years working with military radars ranging from short range radars to detect explosions up to airborne anti-submarine and air tracking radars. that are some of the best systems made to date and can I can absolutely put my hand on my heart and say none of those systems are that good. But basically it’s just my education opinion in the end

 

3 hours ago, nighthawk2174 said:

Not really they are comparable they work of the exact same principles.  Also It was not a specific radar but a generic con-scan FCR with MTI.

That depends on what systems. A lot of Sam sites work as a network and they have great advantages over air to air radars. Remember the Aim-120 is a small tracking radar not a search radar. One is they can search and listen at the same time greatly enhancing their accuracy. They are usual backed up but much more powerful systems that allow them to have much greater search modes and more processing power. They are also usually fairly reliant on user input and not completely automated like the ones in our fighters and missiles

 

3 hours ago, nighthawk2174 said:

I don't think that doppler processing is at all overrated plus it doesn't work alone either there are other mechanisms that support each other.

I’m not saying it should be disregarded or that it useless because it is very important but this community does put into a higher power then what it actually is. There are many many features to a radar and they all play a much more important role then Doppler. In fact Doppler can not even work effectively without these features doing their job first. Making the Doppler a tool that’s towards the back of a chain of tools the radar is using and it is these features that some people are trying to get across that Doppler isn’t this magical thing that solves all problems. When in fact many problems have to be solved first before Doppler can be considered.

3 hours ago, nighthawk2174 said:

Sure but is that effect even enough to make a difference?  Based on what i've read I don't really think it has much noticeable impact especially with modern radars.

And this is the most important point of ALL. No one here knows this answer, I highly doubt a fighter pilot who shoot these missiles would even know the true data. A lot of this kind of data are very tight secrets that the manufacturer and a close few actually get privileged to know this information. So I guess this is where ED listen to what their SME’s say over what material there is available on the internet. They are working close with military’s around the world and developing systems for them that we as common folk don’t get access to, this will be giving them real knowledge that can’t be read about on the internet

3 hours ago, nighthawk2174 said:

No all of these features are there to reject clutter and keep the target locked. 

I can’t speak for the Aim-120 but I can have a fairly good educated guess as to what anti-clutter circuits it will have and there are at least 3-5 other anti-clutter circuits that will be taking effect before the radar narrows downs enough spikes to interrogate, before it considers the Doppler within a pulse but this will be heavily decided by what aspect the radar is looking at the contact with other clutter. 2 of these features could very well completely ignore the radar return that has the contact within it but this is mostly done to make sure the antenna doesn’t burn out but it has a anti-clutter side effect. But due to insane PRF many other pulses will be making it through.

 

3 hours ago, nighthawk2174 said:

Hence why its an integrative (not sure if that's the correct word) proces, it aggregates a bunch of returns over a short time.  And also how would this problem cause an immediate break lock?

This is my main point that’s being missed. It doesn’t have to create an immediate break lock. Chaff needs to introduce problems for the radar to solve. For a simple example is if the chaff is creating such a massive return the radar MAY need to change search modes (I’m speculating here cause I don’t know what the actual search patterns is does or if it even has multiple modes) this will mean a different set of anti-clutter circuits a different PRF a different pulse width so a moment in time that has delayed its tracking ability. I doubt the Aim-120 would actually change or even has multiple search modes with such a short range radar but I hope this is at least showing the point I’m trying to achieve.

3 hours ago, nighthawk2174 said:

I completely disagree how it was before was far more representative imho based on all of the various papers that i've linked in this thread.

Like I stated before. A small tracking radar on the Aim-120 was definitely better then any of the most power search radars that I’ve ever used in my time.

Edited March 20, 2021 by Blinky.ben

[GGTharos]

49 minutes ago, Blinky.ben said:

18 years working with military radars ranging from short range radars to detect explosions up to airborne anti-submarine and air tracking radars. that are some of the best systems made to date and can I can absolutely put my hand on my heart and say none of those systems are that good. But basically it’s just my education opinion in the end

 

Cool, what systems?  If you can tell.

 

Quote

That depends on what systems. A lot of Sam sites work as a network and they have great advantages over air to air radars. Remember the Aim-120 is a small tracking radar not a search radar. One is they can search and listen at the same time greatly enhancing their accuracy. They are usual backed up but much more powerful systems that allow them to have much greater search modes and more processing power. They are also usually fairly reliant on user input and not completely automated like the ones in our fighters and missiles

 

Didn't most of this end with PATRIOT and things like the Sentinel radar?

 

Quote

And this is the most important point of ALL. No one here knows this answer, I highly doubt a fighter pilot who shoot these missiles would even know the true data. A lot of this kind of data are very tight secrets that the manufacturer and a close few actually get privileged to know this information.

 

Fairly certain you're wrong on this, at least in a bunch of cases.  This data is very important and likely available in the vault.  Maybe not the raw data, but the data needed to form tactics around this knowledge.

 

Quote

So I guess this is where ED listen to what their SME’s say over what material there is available on the internet.

 

The SMEs say nothing.   We've heard SMEs say the 120 should be a death ray inside 8nm for example - that doesn't say much.

 

Quote

2 of these features could very well completely ignore the radar return that has the contact within it but this is mostly done to make sure the antenna doesn’t burn out but it has a anti-clutter side effect. But due to insane PRF many other pulses will be making it through.

 

Self-protection chaff is never going to be effective enough to cause a gain drop-out IMHO.   Let me be clear:  We have studies here performed by the USAF itself, showing that chaff itself can only get up to so much RCS before its effectiveness is asymptotically limited.

 

Quote

Chaff needs to introduce problems for the radar to solve. For a simple example is if the chaff is creating such a massive return the radar MAY need to change search modes (I’m speculating here cause I don’t know what the actual search patterns is does or if it even has multiple modes) this will mean a different set of anti-clutter circuits a different PRF a different pulse width so a moment in time that has delayed its tracking ability. I doubt the Aim-120 would actually change or even has multiple search modes with such a short range radar but I hope this is at least showing the point I’m trying to achieve.

Like I stated before. A small tracking radar on the Aim-120 was definitely better then any of the most power search radars that I’ve ever used in my time.

 

Most of this discussion is about a 120 or really any radar already in STT - check thread title.   I agree that problems can be caused by chaff when searching or transitioning from search to track, but that's not what we're talking about.  And even then, the missile already has an idea of what it's searching for - range, doppler, angle gates.

As far as search patterns and modes, all we know is that the 120 goes active, searches in HPRF and may or may not track at this point, and at some point when close enough it transitions to MPRF for track (Don't know about search).

Edited March 20, 2021 by GGTharos

[Blinky.ben]

1 hour ago, GGTharos said:

Didn't most of this end with PATRIOT and things like the Sentinel radar?

Do you mean as for the User input stuff? If so I mean the user has the ability to manipulate the controls and setting/modes but yes they can just walk away and it will run themselves.

 

2 hours ago, GGTharos said:

Cool, what systems?  If you can tell.

Yeah sure my first radar I worked with was the small over weight MSTAR then moved onto GO12 & GO80. Left military and my new role was anti submarine with SV2020 & SV2022 upgraded to the APY-10 and now I do contracted work with a fairly new system. I don’t mean to be rude but I’ll have to leave the new system alone.

2 hours ago, GGTharos said:

The SMEs say nothing.   We've heard SMEs say the 120 should be a death ray inside 8nm for example - that doesn't say much

It would be great to hear from the SME’s ED use.

 

as for the rest of your post I totally agree with everything. Just to make clear I’m not suggesting chaff to be the ultimate defence but it can’t be ignored it does have a level of influence over radars even if it is small. But one small problem isn’t something worth worrying about. However combined with other tactics that all create small problems and we end up with a big problem.

 

All I’m trying to get across is that radars aren’t perfect and it needs assistance from many tools to deal with very common situations and Doppler is just one of those many tools, but it’s not a fool proof system cause it is relying on many other functions. Chaff isn’t something that is just dead weight it does serve a purpose even if the effect is small but it definitely isn’t just something Doppler just eradicates for the radar. There are other systems that will

probably remove chaff before Doppler does or remove the pulse not giving the Doppler feature a chance to kick in. A pulse is a pulse no matter what, the radar has to do something with that pulse. But it does do it at a speed that to this day still boggles my mind

[nighthawk2174]

7 hours ago, Blinky.ben said:

That depends on what systems. A lot of Sam sites work as a network and they have great advantages over air to air radars. Remember the Aim-120 is a small tracking radar not a search radar. One is they can search and listen at the same time greatly enhancing their accuracy. They are usual backed up but much more powerful systems that allow them to have much greater search modes and more processing power. They are also usually fairly reliant on user input and not completely automated like the ones in our fighters and missiles

Right and search radars are a bit of a different ball game than the amraam's TR.

Quote

And this is the most important point of ALL. No one here knows this answer, I highly doubt a fighter pilot who shoot these missiles would even know the true data. A lot of this kind of data are very tight secrets that the manufacturer and a close few actually get privileged to know this information. So I guess this is where ED listen to what their SME’s say over what material there is available on the internet. They are working close with military’s around the world and developing systems for them that we as common folk don’t get access to, this will be giving them real knowledge that can’t be read about on the internet

I mean the pilots i've talked too have all said that the chance of decoying an amraam with chaff is laughably low.  Plus SME's can be wrong too so its best to have a multitude of sources.  Just outright disregarding all the sources i've posted, some even formerly classified, is not the way to go these people making these sources aren't idiots and should be listened too.  

Quote

This is my main point that’s being missed. It doesn’t have to create an immediate break lock. Chaff needs to introduce problems for the radar to solve. For a simple example is if the chaff is creating such a massive return the radar MAY need to change search modes (I’m speculating here cause I don’t know what the actual search patterns is does or if it even has multiple modes) this will mean a different set of anti-clutter circuits a different PRF a different pulse width so a moment in time that has delayed its tracking ability. I doubt the Aim-120 would actually change or even has multiple search modes with such a short range radar but I hope this is at least showing the point I’m trying to achieve.

Like I stated before. A small tracking radar on the Aim-120 was definitely better then any of the most power search radars that I’ve ever used in my time.

 

RIght and the point i'm trying to make is the combination of bloom time, aircraft speed, and the rate that chaff slows down makes it so that in the time it has to make an effect (the res cell of the radar) its not going to be able to do much if really anything at all.  More effect against lower res and less effect against higher res radars.  We're talking much less than half a second for missiles like the amraam.  The amraam being monopulse is even able to solve for multiple targets in the res cell with moderate accuracy with only two pulses.  

Edited March 20, 2021 by nighthawk2174

[GGTharos]

5 hours ago, Blinky.ben said:

Do you mean as for the User input stuff? If so I mean the user has the ability to manipulate the controls and setting/modes but yes they can just walk away and it will run themselves.

 

Pretty much - I understand what you're saying about the multiple antennas etc, but this is effectively going away for SAMs these days.  At most there's a separate antenna for search vs. tracking, but the single antenna does the tracking now, and in the case of PATRIOT it does everything.   Caveat, of course, that 'dish' is actually the one main antenna plus something like 6 antennas for the TVM uplink and a couple more for IFF and other fun stuff (tm).  You can see all of those as separate blisters on the PATRIOT radar 'face'.

 

Quote

Yeah sure my first radar I worked with was the small over weight MSTAR then moved onto GO12 & GO80. Left military and my new role was anti submarine with SV2020 & SV2022 upgraded to the APY-10 and now I do contracted work with a fairly new system. I don’t mean to be rude but I’ll have to leave the new system alone.

 

No worries, most people understand that 'we don't talk about that' means 'we don't talk about that'.   That doesn't mean we won't continue to speculate, just that we know you can't answer    Isn't the APY-10 the P-8's surface search radar?

 

Quote

It would be great to hear from the SME’s ED use.

 

I'm reasonably certain that the SMEs will never say a word about AIM-120s.  Pilots have said various things, including what I've said above but never anything 'useful' in a technical sense.

 

Quote

as for the rest of your post I totally agree with everything. Just to make clear I’m not suggesting chaff to be the ultimate defence but it can’t be ignored it does have a level of influence over radars even if it is small. But one small problem isn’t something worth worrying about. However combined with other tactics that all create small problems and we end up with a big problem.

 

Ok, I understand where you are coming from, I appreciate that you bring in your knowledge and thank You for sharing it.   I wouldn't discourage you from doing it, many of us find this sort of stuff very interesting.

 

Quote

All I’m trying to get across is that radars aren’t perfect and it needs assistance from many tools to deal with very common situations and Doppler is just one of those many tools, but it’s not a fool proof system cause it is relying on many other functions. Chaff isn’t something that is just dead weight it does serve a purpose even if the effect is small but it definitely isn’t just something Doppler just eradicates for the radar. There are other systems that will

probably remove chaff before Doppler does or remove the pulse not giving the Doppler feature a chance to kick in. A pulse is a pulse no matter what, the radar has to do something with that pulse. But it does do it at a speed that to this day still boggles my mind

 

On my end, we mostly talk about what can be done with DCS - DCS has one filter, the doppler filter and that's seriously simplified (you're either within this amount of closure or not), and chaff in DCS acts like a die roll and a flare (fail the die roll, the missile switches to the chaff bundle).   The roll probability is modified by look-down and aspect.   The issue here is that a bunch of us believe that chaff is way too effective at aspects other than on the beam than it should be, and the reason for this is basically this die roll ... this doesn't represent how this process would work in reality IMHO unless you were to slow down the dispensing of chaff, then you might get something approximating a better representation, but ... it would be better to just come up with a better simulation of it than the good-old die roll.

 

Also, if the speed of processing that pulse boggles the mind, an AIM-9X can process the images it sees so fast, that by the time it's done with a frame it may have moved a couple of millimeters.   I really don't know how RF pulses are processed, the image stuff is a lot easier for me because I dabble in machine vision.

Edited March 20, 2021 by GGTharos

[Cmptohocah]

Maybe a stupid question, but what would happen if an 120 was shot at my 6 and I dump all the chaff I have. Would it present a tracking issue? Would the chaff also influence the fuse?

[nighthawk2174]

The fuze I don't know much about so i can't really say much.  But even from directly behind the chaff will still fall out of the res cell of the radar very quickly.  But most importantly it won't stay in a position to be directly in between you and the missile for very long at all making its impact in all probability still rather minimal.  And even while it is chaff isn't 100% opaque to radar.  As was posted earlier the effect here can be likened to a noise jammer.  And as such you can still get returns through it.  

[Blinky.ben]

2 hours ago, nighthawk2174 said:

The fuze I don't know much about so i can't really say much.  But even from directly behind the chaff will still fall out of the res cell of the radar very quickly.  But most importantly it won't stay in a position to be directly in between you and the missile for very long at all making its impact in all probability still rather minimal.  And even while it is chaff isn't 100% opaque to radar.  As was posted earlier the effect here can be likened to a noise jammer.  And as such you can still get returns through it.  

just a couple of questions don’t take this the wrong way they are literally just questions

 

1. When you say the Res cell do we know what the modulation is used and what the pulse compression is for the Aim-120?

 

2. in the scenario asked do we know what effect the chaff would have in terms of AGC which is something that would need to be sorted out before processing begins? This one is very important I would be very interested to know how strong the return would be.

Edited March 21, 2021 by Blinky.ben

[GGTharos]

1 hour ago, Blinky.ben said:

1. When you say the Res cell do we know what the modulation is used and what the pulse compression is for the Aim-120?

 

All we know is that band and that it can be in HPRF or MPRF.  We can also guess at the antenna diameter and we know it's a monopulse antenna, so I suppose you could make some educated guesses for the desired parameters.

 

Quote

2. in the scenario asked do we know what effect the chaff would have in terms of AGC which is something that would need to be sorted out before processing begins? This one is very important I would be very interested to know how strong the return would be.

 

Self-protection chaff usually (from reading certain papers) stop increasing in effectiveness after reaching an RCS of some 40-50m^2.  Not saying it won't kick some form of AGC off, just that I doubt it'll be enough to hide the target aircraft in the noise.

 

As far as DCS goes, tail-on chaff is the most effective with the biggest modification to the 'yes eat chaff please' probability.

Edited March 21, 2021 by GGTharos

[GGTharos]

5 hours ago, Cmptohocah said:

Maybe a stupid question, but what would happen if an 120 was shot at my 6 and I dump all the chaff I have. Would it present a tracking issue? Would the chaff also influence the fuse?

 

Chaff is the enemy of all fuzes, be they radar, laser or whatever.   The ways of dealing with this (for a fuze) are numerous but a) not 100% and b) none of this exists in DCS.

[Blinky.ben]

9 hours ago, GGTharos said:

All we know is that band and that it can be in HPRF or MPRF.  We can also guess at the antenna diameter and we know it's a monopulse antenna, so I suppose you could make some educated guesses for the desired parameters

I see your point however the modulation used is going to help the pulse compression which is the biggest factors to determining the distance a radar can detect between two objects. (Res cell)

 

Range resolution is probably our biggest factor here and there are a few modulations that help in this area but they all have disadvantages also. There is one in particular modulation I can think off that has the best resolution that I am aware of but With Doppler processing (I say processing cause a Doppler capable radar doesn’t always use Doppler so they can change the process) it creates discrepancies but it maybe be within tolerance, I would be interested in which one it would use.

 

Actually you got me thinking with a discussion we had on another forum with fusing and you might be into something. I’ll PM you.

Edited March 21, 2021 by Blinky.ben

[SgtPappy]

7 hours ago, Blinky.ben said:

I see your point however the modulation used is going to help the pulse compression which is the biggest factors to determining the distance a radar can detect between two objects. (Res cell)

 

Range resolution is probably our biggest factor here and there are a few modulations that help in this area but they all have disadvantages also. There is one in particular modulation I can think off that has the best resolution that I am aware of but With Doppler processing (I say processing cause a Doppler capable radar doesn’t always use Doppler so they can change the process) it creates discrepancies but it maybe be within tolerance, I would be interested in which one it would use.

 

I would think angular resolution is the toughest one right? Range resolution especially with pulse compression from what I understand appears to give very good range resolution in the order of a few m. Meanwhile for A-A radars with fixed shape main lobes, I expect a beaming target being tracked would have a larger angular resolution cell in the order of 100's of m (I think) at a given range, especially for further ranges. 

 

Would you be at liberty to discuss your ideal modulation type here? I'm very curious.

 

The ability of modern pulse radar processors to integrate pulse quadrature returns allows then to separate closely-spaced targets at separation distances smaller than the res cell angular spacing which is something I would think AMRAAMs and the like can do, but I am unsure that older radars would have had this ability since it is greatly enhanced by multiple (usually medium) PRFs that are usually present in modern digital MPRF modes. I would think this is why a fighter must maneuver in the beaming plane to spread chaff which has to be spammed to make it look like the rapid-blooming chaff is a part of the aircraft. Have I got the right idea?

 

No idea how effective that would be these days.

Edited March 22, 2021 by SgtPappy

[nighthawk2174]

On 3/22/2021 at 12:09 AM, SgtPappy said:

I would think angular resolution is the toughest one right? Range resolution especially with pulse compression from what I understand appears to give very good range resolution in the order of a few m. Meanwhile for A-A radars with fixed shape main lobes, I expect a beaming target being tracked would have a larger angular resolution cell in the order of 100's of m (I think) at a given range, especially for further ranges. 

 

It was my understanding that angular resolution is frequency dependent no?  Even then if the resolution is similar to the size of the main lobe the chaff wouldn't stay in the res cell for long anyway especially if the target is moving really quickly.  Its probably also part of the reason chaff's stated maximum effectiveness is near the notch, its where the res cell is the largest.  Plus on the separation of targets inside the resolution cell it is my current understanding that monopulse systems are quite capable of doing this due to the way they work.

 

 

Edited March 25, 2021 by nighthawk2174
Added a bit more to post

[SgtPappy]

On 3/24/2021 at 8:08 PM, nighthawk2174 said:

It was my understanding that angular resolution is frequency dependent no?  Even then if the resolution is similar to the size of the main lobe the chaff wouldn't stay in the res cell for long anyway especially if the target is moving really quickly.  Its probably also part of the reason chaff's stated maximum effectiveness is near the notch, its where the res cell is the largest.  Plus on the separation of targets inside the resolution cell it is my current understanding that monopulse systems are quite capable of doing this due to the way they work.

 

Yea I have the same text, it's a very good book. and yes, the angular portion of the res cell is determined by the wavelength size to the aperture ratio. The excerpt from the book shows an engagement range of 6 km = 3.23 nm - that's a very very short range and one which, as you said, would probably not be affected by chaff of a fast beaming target. At longer ranges, say, 8 nm or more (maybe as short as 5 nm), an X-band radar with an aperture of ~0.85 m would give an angular resolution in the order of ~2.5 degrees. At 5 nm, the crossing range in the cell is ~404 m and at 8 nm it's ~646 m. Not huge of course, but seeing as how rapid bloom chaff spreads to max RCS between 0.2-0.5 seconds, maneuvering while notching and adding chaff could have some effect. I'm not convinced that it would do much against the AIM-120C, but we have real world accounts of an F-15 pilot firing an AIM-120A and having it get notched by a MiG-29 between 12 and 7 nm or something like that.

 

I'm still doing my research but as I understand, the quadrature component of the monopulse signals (historically only the in=phase was taken) need to be integrated in order to resolve targets that are closely spaced. Monopulse of course has a great capability to track an RCS centroid within values much smaller than the radar res cell, but I believe if the RCS is scintillating, this is made more difficult from what I've read so far. A maneuvering fighter will not have a constant RCS and neither will the chaff. Older radars would likely have issues with this but I'm thinking the AMRAAM may have this quadrature integration capability.

[GGTharos]

AMRAAM probably had more computing power than some of the radars that support it back in the time it came out.  To add to this, there are filters that will deal with scintillation, and there are filters that can tell chaff from other types of reflections.

[SerialCaveman]

First of all, hello to everybody, it's my first post on forum

 

Wouldn't it be a no-brainer for AiM-120, at least in C variant, to implement some kind of Kalman filter? It should be then able to estimate target acceleration. Then, when monopulse solution would like to start tracking chaff instead of airplane, estimated target acceleration should fly throug the roof, and probably some kind of check should disregard current radar data as invalid.

Then, with no valid radar data, Kalman target trajectory estimation woud be used in further tracking loop iterations not only for antenna pointing, but also for guidance, with gradually increasing size of doppler and range gates. That is, until valid target (not that far of estimated position) is detected, or else - radar returns to search mode.

[GGTharos]

Great questions - there are no Kalman filters in the simulation, and don't expect any to show up.   In fact, there no tracking gates either.   In-game the missile is told to track object #1234 and when countermeasures show up they roll a die to see if the missile will switch to it.

 

I think we'd all love to see this stuff but setting expectations is also important.

Edited March 30, 2021 by GGTharos

[SerialCaveman]

Of course, I wouldn't search for implemented Kalman in DCS code (except most probably F-14). I rather wanted to make a point, that rockets jumping from 300m/s airplane to 0 m/s chaff cloud is - to say at least - not realistic. Not only because of range and Doppler gating, but also thanks to kinematic filters  - even when missile is notched. Hell, if i recall correctly, even R-73 and maybe even R-60M have analogue kinematic filters, that would try to reject flares based on motion characteristics.

 

I also know, that radar simulation for missiles looks like it's non - existent in DCS. Target tracking works most probably like you described. As for quick fix to problem from this topic, I would be satisfied  with simple check after roll die result told missile to go for chaff. If speed difference between tracked airplane and chosen chaff cloud  is greater than  - say - 50m/s, tracking stays on target. If it's less  - switch to chaff. That should make missiles behave in more believable manner.

 

EDIT: I've checked and I was wrong about IR missiles - kinematic filters were implemented later (eg. on Mistral), source:
http://www.mediafire.com/file/nq6i1ja0ds9gqi4/Histoy_of_the_Electro-Optical_Guided_Missiles.pdf/file

Edited March 30, 2021 by SerialCaveman
Information check and correction.

[GGTharos]

I would argue that a constant release of chaff might move the centroid behind the aircraft smoothly.  But, I don't actually know that.

[Cmptohocah]

Everyone here is discussing chaff effects on the AIM-120's radar, but what about its effects on the launching platform's radar?

Think we are missing an important aspect here.

There is virtually 0 effect on it in DCS and yet we have a 7 page disscussion on the effect it has on the AMRAAM.

[GGTharos]

Correct, there was never any effect on the aircraft's own radar in DCS.   The thread is about the 120 though - in the end that's the explosive delivery dart.

 

You can expect chaff to have zero effect on aircraft radars until ED decides otherwise, and, frankly, until radar cells and a whole host of things around radar cells are simulated, chaff effects on aircraft radar will probably be poor, if any.