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AIM-120 still can not chase simple Split S manuever.


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3 minutes ago, GGTharos said:

No need to be dramatic.   Developers can't just magically code up something new.  This takes preparation and care, assuming it even gets green-lighted by any business decision making which may be prioritizing something else.

We all want improvements and it's not fair to say that ED is not making them.

I agree progress can be seen although slower than we would like. The lack of prioritisation on missiles however does anger me it’s no secret. 

That being said… if the scenario in the OP is the intended behaviour and that’s the level of simulation we have to look forward to?…. Then I’m not particularly interested 

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Maestro only said that the missile does what they coded it to do, and works an intended ie. there is no bug.

So while I agree that things move slowly in this area (For us users anyway), I don't think ED are opposed to reviewing how their overall concept for a specific feature (in this case, the look-down clutter and therefore notch) works.

Unfortunately everything is a victim to time constraints in the software business, most of all things that have been coded to completion but where their change is desired.


Edited by GGTharos
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So for a brief period of time the 120 had the ability to counter the notch by searching the target's known flight path, waiting for it to come out of the notch.

People complained that it was too hard to evade and that shall we say ... more advanced behavior is no longer part of the missile's repertoire or at least, on the same level.   Re-coding the clutter effect would certainly make the missile deadlier.


Edited by GGTharos
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Guys, unfortunately I have no time to answer your every question rigth now, so there is drawing with rundown on missile behavior in TS track.

Missile at high altitude and looks down at shallow angle, so footprint is a huge ellipse. Yes, different parts of footprint located at sufficiently different distances  and returns different amount of power, that calculates accroding to radar eqation. Normalized surface RCS depends on angle of incidence as it should. So there is no errors in modeling power of mainlobe ground return I suppose.

Range of notched radial veloctites depends on missile velocity, mainlobe width and mainlobe-surface interseсtion geometry(angles between LOS and surface, missile velocity vector and LOS). Let's consider moment when one of missiles in TS track looses target and estimate notched velocities range at this moment. Missile velocity is 678m/s, missile pitch-AoA angle is -25 degress, seeker deflected 16.5 degress down. Surface radial velocity in direction of LOS will be 678 * cos(-25 +16.5) ~= 671m/s. Radial velocity of upper mainlobe bound will be 678*cos(-25+16.5-7.5) ~= 652m/s. Radial velocity of upper mainlobe bound will be 678*cos(-25+16.5+7.5) ~= 678m/s. So full range of notched velocities is 678-652=26m/s.

Why ranage gating does not help in this case? Because of range ambiguity. For 10KHz PRF maximum unambigious range is 15km. Lower PRFs(provide bigger unamibgous range) not practical for several reasons. From simple geometry calculations we can obtain that closest point of surface lay at ~29km distance and more far point at ~75km. So the range of ground return ranges is around 46km. Due to range ambiguty ground return fill all range bins 3 times (46/15~=3). Dispite of long ditances such return still may mask target due to huge footprint area.

Why missile do not extrapolate target position after lock loosing? It's extrapolete, but not very good due to lack of datalink updates. When seeker looses target missile guides on target INS-predicted position, but INS cant predict manuevers.

 

notching.png

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51 minutes ago, Маэстро said:

Guys, unfortunately I have no time to answer your every question rigth now, so there is drawing with rundown on missile behavior in TS track.

Missile at high altitude and looks down at shallow angle, so footprint is a huge ellipse. Yes, different parts of footprint located at sufficiently different distances  and returns different amount of power, that calculates accroding to radar eqation. Normalized surface RCS depends on angle of incidence as it should. So there is no errors in modeling power of mainlobe ground return I suppose.

Range of notched radial veloctites depends on missile velocity, mainlobe width and mainlobe-surface interseсtion geometry(angles between LOS and surface, missile velocity vector and LOS). Let's consider moment when one of missiles in TS track looses target and estimate notched velocities range at this moment. Missile velocity is 678m/s, missile pitch-AoA angle is -25 degress, seeker deflected 16.5 degress down. Surface radial velocity in direction of LOS will be 678 * cos(-25 +16.5) ~= 671m/s. Radial velocity of upper mainlobe bound will be 678*cos(-25+16.5-7.5) ~= 652m/s. Radial velocity of upper mainlobe bound will be 678*cos(-25+16.5+7.5) ~= 678m/s. So full range of notched velocities is 678-652=26m/s.

Why ranage gating does not help in this case? Because of range ambiguity. For 10KHz PRF maximum unambigious range is 15km. Lower PRFs(provide bigger unamibgous range) not practical for several reasons. From simple geometry calculations we can obtain that closest point of surface lay at ~29km distance and more far point at ~75km. So the range of ground return ranges is around 46km. Due to range ambiguty ground return fill all range bins 3 times (46/15~=3). Dispite of long ditances such return still may mask target due to huge footprint area.

Why missile do not extrapolate target position after lock loosing? It's extrapolete, but not very good due to lack of datalink updates. When seeker looses target missile guides on target INS-predicted position, but INS cant predict manuevers.

 

notching.png

So you are saying you are range gating with HPRF yeah of course that isn't going to work at all if your Range ambiguity is as large as your seekers detection range. What exactly is the point of that feature then.

Also HPRF seekers start to have good range ambiguity at very close ranges, once you get close enough that you are receiving returns before the next pulse goes out. it should be quite possible to have good range ambiguity at 2-3 miles with an HPRF X band seeker.

Range gating with HPRF is completely pointless so if this was known why did you implement it like this.

And why is this not using MPRF which does not have any of this issue.

Regarding the INS..... your telling me it has to exactly match the predicted INS cue, the INS cue doesn't have error bars based on last prediction and how long its been since it saw it, it just says straight line and gives up even if it sees another target magically appear out of the notch?

And that also doesnt hold up with why all the missiles pitched UP when the target went into the notch, if they had any kind of predictive tracking through their INS, the last they saw the target was going DOWN before it entered the notch, so they should have at lost track pitched DOWN towards their last cue not UP.

Here is the last instant before the notch. I've circled roughly where the missiles should think the target is going. Upon loss of track should they not point at that point and look for the target again?

image.png

Instead They start to pull up away from that intercept point the instant they get notched.

image.png

It also cant predict a turn? The target was turning towards MLC, THE MOST DOMINANT THING in the doppler spectrum (especially in HPRF) that has been known about since we started operating with pulse doppler radars, and it has zero logic to go..... maybe the target will come out of the notch in a moment, and it was turning?

 

This is all before I point out that the F-16 turned its belly to the missile revealing the massive RCS (compared to its nose or even side on profile) of its wings, and tail surfaces perpendicular to the missiles seeker. So it should have seen an absolutely massive amplitude spike even though yes there is all that ground clutter. 

There is a lot of ground clutter but the ground clutter is diffuse, and not nearly as reflective as the metal F-16 directly in front of it.

The target return from that RCS that is at 2-3 miles that just flashed a reflective billboard at the missile isn't enough to keep it visible above main lobe clutter which while large is also 22 miles away down the direct line of sight. You are also assuming that the radar once in track isn't angle gating the target and ignoring all returns that aren't within a very narrow window around the target.... precisely to mitigate this kind of issue and increase SnR. 

Finally this entire lookdown happens over water. Unless you are modelling a severe sea state, water has nowhere near the direct clutter return that land does, most of the energy in this scenario is reflected off the surface long of the target, yes some will still be coming back, but not nearly as much.

So yeah for what you've implemented working as intended I guess, but I question why range gating was implemented on a radar (or mode of the radar) that it is apparently useless on, and there are so very many other things that a computerized missile of this sort can do to combat this. The notch is a known feature of working with Pulse doppler radars and has been for over 60 years, that a very modern missile as you have implemented it has zero effective countermeasures against it seems rather wrong.

Now if you were to make this in MPRF, that's a completely different discussion, and is what everyone was assuming.


Edited by KlarSnow
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48 minutes ago, Маэстро said:

...missile pitch-AoA angle is -25 degress...

Please don't hate me, but pitch and AoA are two different things.
Pitch is angle relative to the horizont, and AoA is angle between wing's chord-line and the airflow.

Cmptohocah=CMPTOHOCAH 😉

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44 minutes ago, KlarSnow said:

 

 

 

10KHz is not HPRF. Its a lower bound of MPRF. RCS increasing at perpendicular angles of sight is also implemented and gives up 40 times increasing in RCS. Before saying somthing about visibility of tagets above clutter it's better to calculate it. Otherwise it's just assumptions.

5 minutes ago, Cmptohocah said:

Please don't hate me, but pitch and AoA are two different things.
Pitch is angle relative to the horizont, and AoA is angle between wing's chord-line and the airflow.

I know that. pitch-AOA means pitch minus AoA, that gives direction of velocity vector.

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You should easily be able to get to .1 NM with an MPRF radar for range ambiguity. Multiple miles of range ambiguity is a characteristic of HPRF radars, not MPRF ones.

Unless you are saying the radar isnt using a PRF jitter in order to solve the range ambiguity problem, which is what.....every MPRF radar does.

Ok, so what I have gathered is you are simulating a single PRF MPRF seeker, which at first glance exactly as you have depicted here....is functionally useless. Which is why EVERY FUNCTIONAL VERSION OF MPRF in use.... uses a PRF jitter in order to give it very accurate range and velocity measurement with no ambiguity. you can find many MANY papers on this and how this works, and this is what everyone has assumed you are implementing when you say MPRF. 

So yeah again, working as intended, but not realistic for any MPRF radar that I'm aware of in a military context.

My question now, is why did you implement a useless range gating feature on a radar that cannot exploit it? Should you not have researched and added MPRF Jitter first? Have you researched this type of radar at all? Because to me it looks like you are running through the entire timeline of radar research in the 1960's and 70's where scientists around the world figured this out. Instead of using the ample resources that are available online that tell you how this all works.


Edited by KlarSnow
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Why not, this paper seems to think you can do exactly what you are saying it cannot.

As does just about any other you go and look at, where is your source that extended clutter prevents MPRF from resolving targets. Because every source I, and everyone here but apparently you has seen, says exactly the opposite. Every source on MPRF says MPRF has range and velocity ambiguity, but with techniques like PRF jitter and various processing techniques it is the most reliable method of tracking targets at all aspects in lookdown.

MPRF is specifically chosen to help with sidelobe and main lobe clutter because it reduces the amplitude in the range cells

https://calhoun.nps.edu/handle/10945/5544

What exactly is the reason this does not work?

And seriously it takes 30 seconds to google a research paper that is explicitly saying your claim is incorrect.

This is why everyone is getting so utterly frustrated with how this guidance and radar stuff is going. There are blatantly clear sources that say how this works and whoever is designing these projects appear to be explicitly avoiding any of these for some unknown reason.


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30 minutes ago, Маэстро said:

10KHz is not HPRF. Its a lower bound of MPRF. RCS increasing at perpendicular angles of sight is also implemented and gives up 40 times increasing in RCS. Before saying somthing about visibility of tagets above clutter it's better to calculate it. Otherwise it's just assumptions.

I know that. pitch-AOA means pitch minus AoA, that gives direction of velocity vector.

So RCS increasing when side on is implemented now?

 

Also I know that there are references even the AIM-7 docs to "anti-Split S logic".  Exactly what this entails is not discused but its not hard to make a reasonable guess.  Its almost certaintly just a damper put on the acceleration command if the targets angular position and velocity meet a certain set of criteria.  As such the flight path would look like the red line below instead of green which is what it does now:

1 hour ago, KlarSnow said:

So you are saying you are range gating with HPRF yeah of course that isn't going to work at all if your Range ambiguity is as large as your seekers detection range. What exactly is the point of that feature then.

You can solve for range ambiguity even in HPRF just use PRF switching.

1 hour ago, KlarSnow said:

Also HPRF seekers start to have good range ambiguity at very close ranges, once you get close enough that you are receiving returns before the next pulse goes out. it should be quite possible to have good range ambiguity at 2-3 miles with an HPRF X band seeker.

Sorta, HPRF seekers are highly ambigous in range so i'm not sure if the ku/ka band amraam seeker would even have an unamiguous range of even that far.

1 hour ago, KlarSnow said:

Range gating with HPRF is completely pointless so if this was known why did you implement it like this.

Its hard to range gate with HPRF as due to the range ambiguities its hard to seperate clutter from the target when putting returns into the range bins.

1 hour ago, KlarSnow said:

And why is this not using MPRF which does not have any of this issue.

Exactly

1 hour ago, KlarSnow said:

The target return from that RCS that is at 2-3 miles that just flashed a reflective billboard at the missile isn't enough to keep it visible above main lobe clutter which while large is also 22 miles away down the direct line of sight. You are also assuming that the radar once in track isn't angle gating the target and ignoring all returns that aren't within a very narrow window around the target.... precisely to mitigate this kind of issue and increase SnR. 

Finally this entire lookdown happens over water. Unless you are modelling a severe sea state, water has nowhere near the direct clutter return that land does, most of the energy in this scenario is reflected off the surface long of the target, yes some will still be coming back, but not nearly as much.

So yeah for what you've implemented working as intended I guess, but I question why range gating was implemented on a radar (or mode of the radar) that it is apparently useless on, and there are so very many other things that a computerized missile of this sort can do to combat this. The notch is a known feature of working with Pulse doppler radars and has been for over 60 years, that a very modern missile as you have implemented it has zero effective countermeasures against it seems rather wrong.

Now if you were to make this in MPRF, that's a completely different discussion, and is what everyone was assuming.

 

Ontop of all of this Monopulse systems are renound for massive S/N gains over even planar arrays.  Which would help even more.  And yes range to ground clutter and type should be factored in I don't know if it is currently.

image.png

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16 minutes ago, Маэстро said:

Oh..you really think I do not know about abmiguty resloving? The thing is.. you can perform such resolving for separate relatively small target. That would not work when you have such extended "target" as clutter.

You absolutly can in MPRF especially in a monopulse seeker with its extremely good range resolution, especially in mprf.  And considering the amraam's lack of need for long range I don't doubt its pulse width isn't quite small fractions of a microsecond.  Not to mention other techniques developed to break out closely spaced contacts.  Which monopulse seekers are capable of determing and even partially solving for multiple contacts inside its resolution cell.


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3 minutes ago, KlarSnow said:

Why not, this paper seems to think you can do exactly what you are saying it cannot.

As does just about any other you go and look at, where is your source that extended clutter prevents MPRF from resolving targets. Because every source I, and everyone here but apparently you has seen, says exactly the opposite. Every source on MPRF says MPRF has range and velocity ambiguity, but with techniques like PRF jitter and various processing techniques it is the most reliable method of tracking targets at all aspects in lookdown.

MPRF is specifically chosen to help with sidelobe and main lobe clutter because it reduces the amplitude in the range cells

https://calhoun.nps.edu/handle/10945/5544

What exactly is the reason this does not work?

 

PRF jitter has issues it reduces range what radars use now if PRF switching.  You switch between a few distinct PRF's usually 3-4 and get the same effect without as many issues.

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53 minutes ago, KlarSnow said:

My question now, is why did you implement a useless range gating feature on a radar that cannot exploit it? Should you not have researched and added MPRF Jitter first? Have you researched this type of radar at all? Because to me it looks like you are running through the entire timeline of radar research in the 1960's and 70's where scientists around the world figured this out. Instead of using the ample resources that are available online that tell you how this all works.

Keep the feedback constructive please. 

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23 minutes ago, nighthawk2174 said:

You absolutly can in MPRF especially in a monopulse seeker with its extremely good range resolution, especially in mprf.  And considering the amraam's lack of need for long range I don't doubt its pulse width is quite small.  Not to mention other techniques developed to break out closely spaced contacts.

Ok, then please, tell how you will resolve ambuguties and seprate target from clutter signal if all range bins filled with clutter? 

25 minutes ago, nighthawk2174 said:

So RCS increasing when side on is implemented now?

A long time ago

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Not trying to imply anything, just honestly quite curious as to why these things have been prioritized and then implemented in an apparently nonfunctional manner, I quite honestly think this entire conversation has been quite constructive, because it at least has shown exactly where the disconnect between your community and at least one of your staff is regarding how radars work.

I apologize if my incredulity came off harsh.

This should be really easy. The paper I just posted describes exactly what maestro is saying is impossible, somebody at ED read it please. There are many many like it and they are not hard to find.

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7 minutes ago, Маэстро said:

A long time ago

 

Is this a different issue? It seems like the issue may still be present if I'm following correctly.

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1 hour ago, Маэстро said:

Ok, then please, tell how you will resolve ambuguties and seprate target from clutter signal if all range bins filled with clutter? 

A long time ago

Part of what's going on here too, aside from mprf stuff as i'm not quite up far enough in my reading to know the exact answer I know it can be done though.  We can't ignore S/N either, i've seen missiles notched at less then two miles.  Except that there's a ton of things that should make the target compete even against a large MLC.  The STT nature of the track ensures that integration time is extremely high effectively infinite, monopulse itself also has S/N benefits, side on RCS will be huge as well, the employment of PDI will also help.  The type of terrain would also be important:

image.png

 

https://patents.google.com/patent/US4559537

method of tracking targets in MLC patented by Raytheon in 1985 right when AIM-120 development was in full swing.

 

Also from earlier are you using 15deg for the beamwidth for the amraam?  That's huge way beyond a reasonable value.  MACE uses a value of ~3-4deg

 

Edit:

The video posted by Vatikus is exactly how you deal with mprf ambiguities i'm still working on understanding the exact mechanisms behind mprf but as shown in the vid it can be done easily.  There's a reason MPRF is so widly used.


Edited by nighthawk2174
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1 hour ago, KlarSnow said:

Why not, this paper seems to think you can do exactly what you are saying it cannot.

As does just about any other you go and look at, where is your source that extended clutter prevents MPRF from resolving targets. Because every source I, and everyone here but apparently you has seen, says exactly the opposite. Every source on MPRF says MPRF has range and velocity ambiguity, but with techniques like PRF jitter and various processing techniques it is the most reliable method of tracking targets at all aspects in lookdown.

MPRF is specifically chosen to help with sidelobe and main lobe clutter because it reduces the amplitude in the range cells

https://calhoun.nps.edu/handle/10945/5544

What exactly is the reason this does not work?

And seriously it takes 30 seconds to google a research paper that is explicitly saying your claim is incorrect.

This is why everyone is getting so utterly frustrated with how this guidance and radar stuff is going. There are blatantly clear sources that say how this works and whoever is designing these projects appear to be explicitly avoiding any of these for some unknown reason.

 

From your own link

clutter_link.jpg

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9 minutes ago, Маэстро said:

From your own link

clutter_link.jpg

Keep reading

there is a lot more pages to that

image.png

Page 81, that's his conclusion on what a 10Khz PRF jittered radar could see at 9000 feet just by randomly picking PRF's, not even optimizing it, just randomizing it.

image.png

And Page 88 shows that by optimizing it at 9000 feet above the ground his theoretical 10Khz MPRF radar can detect targets out to 23 nautical miles in clutter.

And this is according to Nighthawk and others the bad way of doing this that reduces your detection range. PRF switching as they said should be even better...

 

To be honest this isn't even the best paper about this, it just was one of the first to pop up, and it is fairly easy to understand.


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25 minutes ago, nighthawk2174 said:

Part of what's going on here too, aside from mprf stuff as i'm not quite up far enough in my reading to know the exact answer I know it can be done though.  We can't ignore S/N either, i've seen missiles notched at less then two miles.  Except that there's a ton of things that should make the target compete even against a large MLC.  The STT nature of the track ensures that integration time is extremely high effectively infinite, monopulse itself also has S/N benefits, side on RCS will be huge as well, the employment of PDI will also help.  The type of terrain would also be important:

image.png

 

That all well known. At the moment very low S/N chosen(2 dB only) for target detection assuming effect of PDI. Regarding sigma values - now its some averaged value depending on incidence angle.

25 minutes ago, nighthawk2174 said:

https://patents.google.com/patent/US4559537

method of tracking targets in MLC patented by Raytheon in 1985 right when AIM-120 development was in full swing.

I saw this earlier. it assumes unambiguous range.

25 minutes ago, nighthawk2174 said:

Also from earlier are you using 15deg for the beamwidth for the amraam?  That's huge way beyond a reasonable value.  MACE uses a value of ~3-4deg

That's correct value(you may estimate it knowing antenna diameter and carrier frequency). You can't obtain narrow beam with small dish. Also 15 degrees circle you can see on F-18s HUD in amraam visual mode. For AIM-7 it will be 12 degrees.

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2 hours ago, nighthawk2174 said:

You absolutly can in MPRF especially in a monopulse seeker with its extremely good range resolution, especially in mprf.  And considering the amraam's lack of need for long range I don't doubt its pulse width isn't quite small fractions of a microsecond.  Not to mention other techniques developed to break out closely spaced contacts.  Which monopulse seekers are capable of determing and even partially solving for multiple contacts inside its resolution cell.

I don't think anyone said that HPRF/MPRF ambiguity cannot be solved for most conditions. For a target only the range bins that correspond to its doppler frequency need to be checked, and there will only be a few peaks. So solving the ambiguity will be simple.

But when the target is in the notch, the range bins that corrensponds to its doppler will also be full of ground return. So you cannot just search for single peaks and compare their positions over multiple PRFs unless the target really stands out due to favourable geometry of the setup.

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