Counter Stealth

[kcran567]

Straight planform edges are good for a spiky RCS where the radar returns are concentrated in lobes. This was one of the major breakthroughs of stealth - you can't actually not reflect anything, so if you try to reflect EVERYTHING in the smallest number of directions the chances of detection are pretty small.

The problem with earlier attempts at stealth e.g. the NAA Flying Banana was that curves give a proportionally smaller radar return but over a much wider range of angles. Its slightly hard to see in all directions rather than (like the F-117) near invisible in all but a few.

Speculation: everything since the F-117 has combined straight edges with some curves, so its not essential to have all straight edges. Presumably at some point, it may be desirable to stop concentrating major returns in a few directions and instead try for minimum returns in all directions to achieve "ultra stealth", assuming the RCS modelling and materials are up to it.

The black and white picture seems to show a flying wing with with compound sweep, more sweep in front and less at the wingtips.

Can anyone elaborate a little as to why Low Frequeancy Radars are useful in detecting stealth aircraft. Are they useful in a tactical sense? Might the T-50 have some equipment that is operating in the low frequency band to assist targeting and integrated with an IR sensor?
Also, the Gripen NG is going to really focus on next generation IR sensors to try to defeat stealth. What are the thoughts on this approach to counter stealth?

 

[quellish]

Can anyone elaborate a little as to why Low Frequeancy Radars are useful in detecting stealth aircraft. Are they useful in a tactical sense?

Because the physical size of the wavelength is greater than the physical size of the aircraft being observed. The lower the frequency, the larger (longer) the wavelength.

 

[TomS]

Can anyone elaborate a little as to why Low Frequeancy Radars are useful in detecting stealth aircraft. Are they useful in a tactical sense? Might the T-50 have some equipment that is operating in the low frequency band to assist targeting and integrated with an IR sensor?
Also, the Gripen NG is going to really focus on next generation IR sensors to try to defeat stealth. What are the thoughts on this approach to counter stealth?

Low-frequency radars basically "see" the overall dimensions of the aircraft, not specific reflective surfaces. But as quellish noted, they only work when the wavelength of the radar is substantially larger than the aircraft's major dimensions.


You will not see low-frequency radars on fighters, because the antennas are very large (meters across at least). They also tend not to be very precise (diffraction limits and so forth), meaning they're only usually good for general cueing and warning. Useful, but you still have to get a high-frequency fire control set to lock on.

 

[Sundog]

Useful, but you still have to get a high-frequency fire control set to lock on.

Or a good IR system to lock on.

 

[LowObservable]

The susceptibility of some stealth designs to VHF was well known before Have Blue. The answer was to route around them, design against them (B-2) or rely on the inability of higher-frequency radars to lock on to a VHF cue.
AESA VHF radars, fused with high-power tracking radars and IR, make the last option unworkable. You now need to jam or destroy the VHFs or go to a broadband stealth design.

 

[sublight_]

Can anyone elaborate a little as to why Low Frequency Radars are useful in detecting stealth aircraft. Are they useful in a tactical sense?

Because the physical size of the wavelength is greater than the physical size of the aircraft being observed. The lower the frequency, the larger (longer) the wavelength.

You'd have to go down to 50 Megahertz to get a good 20 foot wavelength. An array like that is not going to be very mobile, if even practical at all. So (theoretically) if you have a platform that is diamond shaped and more than 20 feet on a side, its going to be real hard to detect even with low frequency.

 

[sferrin]

The susceptibility of some stealth designs to VHF was well known before Have Blue. The answer was to route around them, design against them (B-2) or rely on the inability of higher-frequency radars to lock on to a VHF cue.
AESA VHF radars, fused with high-power tracking radars and IR, make the last option unworkable. You now need to jam or destroy the VHFs or go to a broadband stealth design.

In any case there will be orders of magnitude fewer VHS radars to deal with than those that can detect conventional aircraft. And once they're dealt with we're right back to stealth aircraft of any type being very difficult to target.

 

[SOC]

In any case there will be orders of magnitude fewer VHS radars to deal with than those that can detect conventional aircraft. And once they're dealt with we're right back to stealth aircraft of any type being very difficult to target.

Depends on the environment. "Orders of magnitude fewer"...well, sure, because there can be hundreds and hundreds of other EW radars out there. Look at Russia. At last count there were 68 identified 55Zh6 TALL RACK VHF-band CVLO radars deployed in Russia. At least 100 Nebo-M multi-band mobile systems are being introduced. That's not necessarily a lot compared to the overall number of sensors (I can ID about 700 individual radar sets, and there are a lot more either hidden under geodesic domes or unidentifiable in available imagery), but it's more than enough to give you overlapping, cmplementary coverage over important areas. Give a handful of these to Iran or Syria and it's not that hard to deal with (simply TLAM the crap out of the radar sites and move on), but Russia or China are different scenarios entirely.

 

[sferrin]

In any case there will be orders of magnitude fewer VHS radars to deal with than those that can detect conventional aircraft. And once they're dealt with we're right back to stealth aircraft of any type being very difficult to target.

Depends on the environment. "Orders of magnitude fewer"...well, sure, because there can be hundreds and hundreds of other EW radars out there. Look at Russia. At last count there were 68 identified 55Zh6 TALL RACK VHF-band CVLO radars deployed in Russia. At least 100 Nebo-M multi-band mobile systems are being introduced. That's not necessarily a lot compared to the overall number of sensors (I can ID about 700 individual radar sets, and there are a lot more either hidden under geodesic domes or unidentifiable in available imagery), but it's more than enough to give you overlapping, cmplementary coverage over important areas. Give a handful of these to Iran or Syria and it's not that hard to deal with (simply TLAM the crap out of the radar sites and move on), but Russia or China are different scenarios entirely.

And yet, compared to knocking out all the radars required to make it safe for conventional aircraft, it's a much smaller problem.

 

[SOC]

And yet, compared to knocking out all the radars required to make it safe for conventional aircraft, it's a much smaller problem.

Only relatively speaking. It's still not going to be a simple task given the scale of the networks involved in either Russia or China, with the former obviously being a bigger potential concern right now.

Plus, Russia isn't stupid and has started deploying Pantsyr-S1 (SA-22 GREYHOUND) batteries near important assets specifically for anti-PGM/LACM defense. LACMs can also be picked up and intercepted by other means. Hell, in 1991 Saddam managed to get Tomahawks with old Osa (SA-8 GECKO) systems.

 

[sferrin]

And yet, compared to knocking out all the radars required to make it safe for conventional aircraft, it's a much smaller problem.

Only relatively speaking. It's still not going to be a simple task given the scale of the networks involved in either Russia or China, with the former obviously being a bigger potential concern right now.

Plus, Russia isn't stupid and has started deploying Pantsyr-S1 (SA-22 GREYHOUND) batteries near important assets specifically for anti-PGM/LACM defense. LACMs can also be picked up and intercepted by other means. Hell, in 1991 Saddam managed to get Tomahawks with old Osa (SA-8 GECKO) systems.

True. But JASSM isn't Tomahawk. OTH I think it's long past time they developed a weapon specifically to deal with that kind of setup. Imagine something like an air-launched ATACMS with a stretched booster deploying a hundred or so munitions like this but designed for high speed flight:



Launch the missile from an F-15 (or F-35), maybe 300-400 miles out, and the missile lets the bomblets go outside the range of the defending S-400 site. And all you have to kill are the radars. Anything else would be a bonus.

 

[quellish]

Look at Russia. At last count there were 68 identified 55Zh6 TALL RACK VHF-band CVLO radars deployed in Russia.

How many of those are operating?
How capable are their crews?
How do they train and drill against VLO targets?

 

[marauder2048]

Wonder if Lockheed has flown the F-22 and/or the F-35 against their own Low-frequency AESAs (APY-9 and the MEADS LFS come to mind).
In any event, one hopes there are Western/Allied threat-representative surrogates for these emerging Russian systems.

 

[quellish]

Wonder if Lockheed has flown the F-22 and/or the F-35 against their own Low-frequency AESAs (APY-9 and the MEADS LFS come to mind).

They have.

In any event, one hopes there are Western/Allied threat-representative surrogates for these emerging Russian systems.

There are. RQ-170s aren't the only things at Tonopah.

 

[LMFS]

I want to clarify something: Firstly, the part that you quoted referring to Rayleigh region when the wavelength is longer than the circumference of the aircraft, normally an aircraft is 15-16 m long, so you need HF frequency to view them in Rayleigh region. The interaction of VHF, UHF, L band radar with normal aircraft is mostly in Mie region. In Mie region, the blended curve, serrated edges, serrated panels, conductive paint over gaps, trailing and leading edge treatment, still have great impact on RCS reduction.

Secondly, even though in Rayleigh region stealth design have no impact, in this region RCS will be reduced when wavelength get longer, this is opposite to Mie region. So while I can see OTH-B radar immune to stealth, OTH-SW radar will struggle.

The aircraft is not a sphere but has many geometric elements, some bigger and some smaller. It is not inly the biggest dimension that counts.

Ferrite magnetic RAM can be much thinner than dielectric RAM because their electrical thickness is much greater than mechanical thickness

Yes, still wavelength is an issue and they have the added compromise of weight. I am not making the absolute point that it is impossible to reduce RCS or that stealth is useless. I am saying that current fighter stealth can be countered with certain radar systems. There is always a way to optimize a system and a way to counter it. With the increasing complexity, a moment is reached where air forces can feel the pressure of putting some of their focus rather on attritable platforms than on ultra-expensive really VLO ones. Of course signature managament is here to stay on almost every platform and every air force, because it makes a lot of sense for many reasons.

Low frequency radar has the benefit of making the reflection lobes wider but at the same time, wider lobes resulted in lower intensity. In the photo I posted earlier, you can see that the energy return intensity at 300 MHz is about 0.09% of 10 GHz

The advantage of OTH systems is that they handle monstrous levels of power. So a fraction of the power is still a lot. Nebo-M also uses serious levels of power and added to that, a multiband structure. I don't exactly know how they extract simultaneous information from the different bands but that is apparently how the system works.

Resolution cell isn't a fixed volume, it has the same size as: (vertical beam width)*(horizontal beam width)* (pulse width) so it will get bigger with range.

Sure, it happens at any frequency.

Secondly, Konteyner radars are build with overlapping field because it is an OTH-B radar, and OTH-B radar has very big blind spot around them called the skip zone because they need to be reflected from the ionosphere. This blind skip zone is anywhere from 1000-3000km in diameter

I meant the upcoming Konteyner unit in Kaliningrad and the rest of units that are planed to be built, which will overlap on some regions and will cover the whole border against aerodynamic targets. Since they have a huge range, they can see aircraft at the runway 2000 km away from the borders despite being 1000 km inland. For a small country this skip zone is indeed a problem, for bigger ones it is not.

AESA/PESA radar can perform scan very rapidly in irregular pattern so they won't need to reveal position of the carrier for very long, and the pilot has option to use their radar only once a while.

This is a bit of the same old double standards. E-2D, as Josh_TN mentioned in the original thread where we started discussing this issue, is marketed as having both anti-stealth capability and being capable of target-quality tracking info with a UHF radar, and nobody bats an eyelid. ESM systems on the F-35 are supposed to get tracking quality info out of any emitting source out there and everybody is happy.

An emitting source like a radar, if it is in active scan mode and illuminates a receptor listening, can be seen and located at the single platform level.

geolocate a noncooperative moving airborne target with ESM system is very implausible in most cases because the change of bearing for a fast target at long range and a slow target at close range can be the same. Motion analysis method might allow a guesstimate of the range and target velocity but you need your target to maintain the same course, speed, altitude for a while or your estimation will get a huge error and become useless.

See above, there are different ESM antennas on every modern plane well separated to improve their capability to discern the direction of any emitter they pick up. Just a tiny phase shift is enough for that discrimination method to work.

 

[Ronny]

The aircraft is not a sphere but has many geometric elements, some bigger and some smaller. It is not inly the biggest dimension that counts.

Yes, but smaller parts also have smaller radar cross section. The Rayleigh or Mie scattering of the whole aircraft is order of magnitude greater than the Rayleigh or Mie scattering of the wing tip or something similar

The advantage of OTH systems is that they handle monstrous levels of power. So a fraction of the power is still a lot. Nebo-M also uses serious levels of power and added to that, a multiband structure. I don't exactly know how they extract simultaneous information from the different bands but that is apparently how the system works.

I'm making a general point, not just about OTH radar but low frequency radar. You get bigger specular reflection lobes but pay for that with lower lobes intensity.
OTH radar handle an enormous level of power but the range is also enormous so the power at long range isn't very extreme, because it decrease with 4 root of distance

Nebo M isn't an OTH system, and the principles is very simple, it uses different radar for different frequency, that it.

I meant the upcoming Konteyner unit in Kaliningrad and the rest of units that are planed to be built, which will overlap on some regions and will cover the whole border against aerodynamic targets. Since they have a huge range, they can see aircraft at the runway 2000 km away from the borders despite being 1000 km inland. For a small country this skip zone is indeed a problem, for bigger ones it is not.

The skip zone is often 1000-2500 km in diameter so OTH-B system need very big countries with great land area to be effective. For smaller countries, not so much.

This is a bit of the same old double standards. E-2D, as Josh_TN mentioned in the original thread where we started discussing this issue, is marketed as having both anti-stealth capability and being capable of target-quality tracking info with a UHF radar, and nobody bats an eyelid. ESM systems on the F-35 are supposed to get tracking quality info out of any emitting source out there and everybody is happy.

An emitting source like a radar, if it is in active scan mode and illuminates a receptor listening, can be seen and located at the single platform level.
See above, there are different ESM antennas on every modern plane well separated to improve their capability to discern the direction of any emitter they pick up. Just a tiny phase shift is enough for that discrimination method to work.

I don't think E-2D is a strong as anti stealth assets, most stealth aircraft should be able to attack it before they are detected themselves.
ESM on F-35 should have very easy time geolocate the exact location of any ground emitter.




But to geolocate the exact location of an airborne emitter is a different matter. The technique that rely on phase shift to determine direction is called "Interferometry". But it only let you know the direction of target. Like I said before, it is very important to know the range to target and its velocity as well. The technique that would normally allow geolocation of fixed or slowing moving ground target when used against a quick moving air target will have a lot of ambiguity and inaccuracy.


Even the very dedicate state of the art ESM system such as ALQ-218 on EA-18 only ever advertise the ability to precise geolocate ground emitters because getting anything more than the direction for noncooperative airborne emitter is impractical in most case

 

[Josh_TN]

Hypothetically you can geolocate an airborne emitter with differential time of arrival across several different platforms operating with a datalink, assuming all through platforms can hear the same pulse at once. Practically I don't think that is achievable very often, and at the very least you want a directional datalink like the MADL to share that info, since broadcasting an L band omni directional datalink is a big give away.

 

[Ronny]

Hypothetically you can geolocate an airborne emitter with differential time of arrival across several different platforms operating with a datalink, assuming all through platforms can hear the same pulse at once.

yes, that what I talked about in the other thread. But the low side lobes characteristic of AESA make it quite hard for several platforms to receive the same pulse.

 

[Josh_TN]

It seems unlikely in actual practice. You would probably need some kind of flight geometry tailored to accomplish this and it would probably only work at a long range enough where the detection cell was large enough to include all of the detecting aircraft.

 

[LMFS]

Yes, but smaller parts also have smaller radar cross section. The Rayleigh or Mie scattering of the whole aircraft is order of magnitude greater than the Rayleigh or Mie scattering of the wing tip or something similar

Yet it is widely assumed that the supposedly reflective IRST of the Su-57 would give it away and turn it into non-stealthy. But an entire wing resonating in the frequency of a radar would not...

Nebo M isn't an OTH system, and the principles is very simple, it uses different radar for different frequency, that it.

I know, I meant that I am not aware how the processing of the signal is made, if it is common based on more or less raw data at several frequencies or just a post-processing of the results of three separated radars.

The skip zone is often 1000-2500 km in diameter so OTH-B system need very big countries with great land area to be effective. For smaller countries, not so much.

True, still depending on the country it can help a lot, defending sea and land approaches to the country. But I agree the kind of users that really have a big need of them are big powers with big geographical extension where the radar is both protected inland and capable of covering directly the country borders.

But to geolocate the exact location of an airborne emitter is a different matter. The technique that rely on phase shift to determine direction is called "Interferometry". But it only let you know the direction of target. Like I said before, it is very important to know the range to target and its velocity as well. The technique that would normally allow geolocation of fixed or slowing moving ground target when used against a quick moving air target will have a lot of ambiguity and inaccuracy.

yes, that what I talked about in the other thread. But the low side lobes characteristic of AESA make it quite hard for several platforms to receive the same pulse.

Yes, it is not so ideal but still giving away your presence and bearing is extremely dangerous. All it takes to turn a phase interferometer into a tool for giving targeting info is that the enemy is not flying their planes alone but in couples or wings as it is normally done (not even considering ground passive locators of higher performance resources from the IADS helping there, which would be fully expected). First the radar signals give the direction, next the planes in the wing can separate a few km (or fly already in such way as is known from the MiG-31) and locate the enemy plane at the intersection of the directions their individual interferometers provide. You don't need to receive the same pulse at the different interferometers, since each of the platforms will make its own direction finding. Probably there are other tools like classification of the signal, analysis of the received power and so on, but the one I described above is more than enough IMHO.

That being said, my original points was not even the opponent getting purely passive, target grade information, but just knowing there is an enemy and where it is coming from. I think it is non disputable that a stealth plane does not use radar in scanning mode and would actually be extremely careful to use either it in a reduced sector or directional data links while trying to stay undetected.

 

[Josh_TN]

I feel like the discussion is going into circles a bit. A lower RCS is always going to be more desirable if you don’t have to pay for it. The question is, how much do you want to pay for it. The several countries that can achieve low RCS fighter designs continue to pursue those designs, and the one country that has produced a low RCS bomber design is replicating it, with both of its main competitors duplicating the effort.

We can discuss the abilities of individual fighter designs as amateurs, but the opinions of professionals with regard to low RCS is very apparent.

Edit to add: my point being that there are wavelengths and methods that can defeat low RCS designs, particularly fighter types...but clearly the powers that have the technical expertise to produce them continue to produce them. So we can probably take it for granted that they introduce defensive problems that are not easily overcome even by the nations that produce them. It is notable that the US now seems to employ F117 as aggressor stand ins and is already planning to make first batch F-35s aggressors as well. Low RCS isn’t going to be insurmountable but much like other major avionics like look down/shoot down or digital radio repeaters, it’s going to be how the game is played by top tier players and is a must have, not just something on a parade float.