U.S. army developing encrypted radar waveform | Hacker News Reader

U.S. army developing encrypted radar waveform

thestack.com

60 pointschewymouse40 comments

In the future military radars will increasingly look like directed white noise emissions rather than any sort of steady waveform on a particular frequency. This will make it much harder for targets to apply countermeasures, or even reliably detect when they are being illuminated. High speed signal processing makes it possible to reassemble radar returns that seem almost random into an accurate picture.

Yup. In fact, if you use a technique called spread spectrum emissions you can have your signal below the noise floor but have it still be possible to pick it up because it carries so much redundant information across a massive bandwidth.

https://en.wikipedia.org/wiki/Spread_spectrum

I can't find much information about using SS to go below the noise floor on wikipedia but it is a thing.

GPS is below the noise floor at the receiver, IIRC.

UWB radar is also a thing.

Anti-radar devices will have to go the Russian route and just blast the shit out of every frequency to disrupt radar. It won't help that the radar is shifting frequencies over time if every channel and frequency is filled with strong noise from a jammer.

Barrage noise jammers (to which you refer) have always been the most difficult jammers to deal with in the sensor. The usual countermeasure to them is "region blanking", where the sensor simply stops listening for returns on the azimuth of the jammer.

Fortunately, barrage noise jammers are the easiest to deal with using AGM-88 HARMs.

Edit: Also, I should note that barrage noise jammers have limited bandwidth, and have to trade off bandwidth for power. If the APCN system keeps its operating frequency sufficiently masked it may require multiple jammers to actually interfere with the system sufficiently.

> The AGM-88 High-speed Anti-Radiation Missile (HARM) is a tactical, air-to-surface missile designed to home in on electronic transmissions coming from surface-to-air radar systems.

Figured that's what it was, but I'll save everyone the googling.

Well not really....

1) Jammers are a realy good target for anti-radiation missiles.

2) Jammers are also limited in power and frequency you can't make a jammer that can saturate every frequency multi-spectrum jammers allow you to jam different frequencies but usually not at the same time because you are power limited. So even if you have a jammer with say 50 different physical transmitter if you operate all of them each transmitter will operate at 1/50th of the peak transmission power. Wide spectrum jamming is usually done using timing, radars send pulses based on some specific cycle so what you do is attenuate your jammer to the cycle and frequency which allows you to "effectively" jam multiple radars because you don't have to be transmitting all the time to create false signals.

So this (#2) is what this whole new "encrypted radar" concept is supposed to combat which is cheap and effective wide spectrum radar jammers because today anyone with an SDR and a hacked TV dish can make quite an effective jammer.

"Jammers are a realy(sic) good target for anti-radiation missiles."

Yes, but jammers are cheap and lightweight; missiles are expensive and bulky. And there are other types of jammers that mimic a target: they listen for a radar ping and respond with the simulated target's echo. Such jammers are smarter, more difficult to ignore, and more expensive but they still cost far less than a missile (and weigh far less too).

Barrage noise jammers with sufficient power and bandwidth to effectively shut down radar systems are neither cheap nor lightweight. The ones that are both are merely a nuisance.

You're right. I spoke too soon.

I was thinking of _decoys_, which are typically cheap, light and inexpensive and provide, in the most optimistic of circumstances for the target, a multitude of other indistinguishable "targets."

It's not as effective as you imagine. Noise radar can still operate when the return signal is below the noise floor. It's very difficult to jam because the jamming is uncorrelated with the noise signal. The low power levels make it harder to detect even with modern direction finding / interferometry arrays.

This relates closely to the [Darpa Spectrum Challenge](http://archive.darpa.mil/spectrumchallenge/) that I participated in a couple years ago. The goal was to transmit information in a congested and contested RF environment. I think that they wanted to develop rapid spectrum-aware sensing as well as hard-to-jam signals.

I was literally talking about this yesterday with a friend in the context of military robotics and their control systems. He said those C&C systems would be a huge IW/EW target and my counter was that DARPA was already addressing that through things like the Spectrum Challenge.

As soon as someone learns to detect F35 radar signal, more than half if it's stealth advantage melts away. So far U.S. has only made air-to-ground anti-radiation missiles, but the Russians have tried also air-to-air version.

https://en.wikipedia.org/wiki/Anti-radiation_missile

All this has not gone unnoticed in the Pentagon, so radars like there have probably been in the works for quite some time. F35 sales pitches are probably warming up right now, so news like this are expected.

The only surprise for me is that this comes from the army and not the air force or navy. They probably need to worry about enemy droids. And if they worry about those droids using radar, they need to worry about enemy anti-radiation missiles.

This is probably part of larger picture of U.S. armed forces to avoid using Infra Red Search and Track (IRST). Because that makes stealth planes look bit silly, when you go past ~0,07m^2 radar cross section. At that point you would get parity with detection ranges of common radars and modern IRST sensors, which would be something like 80km for fighter jet sized object. But this would mean no operations in enemy airspace, as flight ceilings are typically around 20km. F35 has RCS 0,01 and F22 RCS 0,001 which is just great for operating in enemy airspace, if the enemy can't detect their radars and lacks IRST.

Currently it seems the best USAF can do about IRST is to pretend it doesn't matter. So if there is any coordination between the branches, the army has to get their own stealth radar against enemy drones. After two decades and gazillion dollars, we probably see subsonic F40-cool-skin, with reflecting mirror finish aluminum body, that eliminates this problem. And power projection and proceed uninhibited.

Why mirror finish aluminum? Current IRST sensors can detect current fighters from tens of kilometers away from sun heated surfaces radiating at IR spectrum. Having orthogonal plates means that sun glare doesn't hit the IR sensor directly, the mirror finish prevents excessive heating and smooth aluminum has very small IR emissivity naturally. Conveniently aircraft are already made from aluminum.

Right now we don't hear about this aluminum shit, because U.S. is still funding some weaponized lasers. Airborne lasers smelled like "overspending" before, but it's really going to smell like bluff when reflecting surfaces increase power requirements some 400%. They already suffer from bad power/weight ratios. But once naval laser "close-in weapon system" has been fielded (because any chance is a good one when you're desperate) we can go back to airplane design.

Sorry, this is bit long. I've had this autistic streak about this subject for past two weeks.

Modern aircraft don't need RADAR that much, they can run the RADAR in passive mode and since they are all equipped with IRST[0] they have other sensors to compensate for the lack of active radar.

[0]https://en.wikipedia.org/wiki/Infra-red_search_and_track

Missiles have their own seeker (CCD/IR/Radar) which are used to guide them to their targets, on modern jet fighters the radars usually need to be activated only for a very short period for a coarse BVR EIP and that's about it.

For (W)IVR engagements the radar is not needed at all as the pilot can see it's target, the missile seeker can then be activated prior to launch and you get a lock from the missile no the on board radar (that's the actual iconic tone lock), and today you don't even need a full (or even any type of lock) as most missiles have Lock After Launch capabilities which will allow the missile to either select a target autonomously or receive a target designation from the pilot after launch.

Also as far as RADAR goes then don't forget that F35's don't fly solo but rather in strike groups meaning that even if they are not accompanied by special missions aircraft that only one of them will have the radar on in active mode and the data will be shared using the combat data link (and the other passive radars can actually use the return signal from the active one to independently identify targets). But the even more common formation will be several strike groups of jets with a special missions aircraft (e.g. AWACS) flying couple of 100's of miles behind them with a much bigger radar that could lock on BVR and BHR targets and transmit the details to the strike aircraft via a datalink.

I don't think any modern fighter yet has all aspect IRST. They are usually mounted above the nose and have somewhat limited field of vision.

Current USAF tactic is probably to illuminate targets with AWACS and engage them from long range with F-22. Then conduct SEAD mission with F35. Pretty much as you said. That's actually somewhat good idea against future enemy stealth fighters, if you can simply increase that AWACS radar power. (Easier said than done, you probably need couple orders of magnitude more power.) But radar guided missile ranges have been increasing recently, S400 should have 400km range. Fighters might be able to dodge that massive missiles, but AWACS plane is probably doomed. And radars tend to show on radar.

Current short and medium range missiles are so good, that as long as you have lock on, the "no escape zone" is quite large. Increase in computation power and seeker resolution has rendered chaff and flares almost obsolete. (Or that's what most sources tell you. They don't get to test those systems in real life engagements too often.) This and combined to off bore-sight launch capability has led analysts to predict mutual kill in any close combat situation involving relatively modern fighters.

One major problem with selling the F35 is to convince other countries that they actually need a flying platform anymore. If missiles are as good as everybody is saying and if Russia, China and India are able to launch stealthy aircraft, why not just buy trucks with IRST sensors and heat seeking SAM missiles? You can buy quite a bunch of such systems with the price of single F35.

F35 flying in a pack and using their radars one at the time? Cool. But if PAK FA has the stealth they claim it will have, you are better off with just IRST, because as completely passive, it doesn't warn anybody about anything. Ditch the radar and get ~400kg more fuel on board, or equally lighter aircraft.

I never made a comment about the F-35's potential performance it's a weapons platform not a fighter jet.

That said the PAK-FA is not in production and given the Russian track record it might never actual enter any production, the procurement that was initially intended for 2007 with a 2016 delivery was halted and with the Russian economy in the toilet it looks like the well will be dry for quite a while.

The Russians had a bet that their gas would fund their rearmament they've had 5 stealth programs in the works with the most advanced (in terms of progression) the PAK-FA costing over 10 bln. which was unprecedented for Russian defense spending.

So currently with the falling gas prices and economic sanctions it almost looks like a repeat of the Reagan era forcing the Russkies to spend them selves out of existence.

I would also take any potential performance of Russian jet with a huge grain of salt they've always looked superior and scary as fuck on paper but every time western Jets faced against them mainly in the middle east the soviet jets were left splattered on the ground, and while it's true that Israeli pilots might have been better trained than their Arab counterparts by all accounts they shot down just as many soviet "advisers" as Egyptian or Syrian pilots.

What you're saying is correct for short term.

I guess my point is that F35 service life is not goint to be four decades long, as it was for F16. It's too optimized for current threat enviroment, which is likely to change a lot in just few decades. Unless China implodes, gas prices remain very low for Russia for several decades in a row. And India suddenly remembers how Mahatma Gandhi was a great guy.

The F35 can also evolve, an F16 block 16/25 is quite a different beast from a modern Block 52/52+ one.

Heck if the F15 gets it's SE variant you could potentially extend it's life for 3 or more decades, and even without it it's probably good for another 20 years or so as it doesn't look like anyone is building a strike fighter with similar payload delivery capabilities and speed.

Heck if the US can find use for it's B52 fleet till ~2050 (which will make it the first aircraft to serve for a whole century) they could probably find a use for an F35.

Heck convert them all to drone and use them as expandable weapon delivery platforms you are unlikely to see much dog fighting in 2030.

Yes you can use it. But F16 was still credible aerial superiority fighter against everybody in 2005. Mostly because of collapse of Soviet union, as there was a decade of low intensity R&D with everything except F-22. Now with latest SAM missiles and long range air-to-air missiles being slowly adopted by everybody, stealth is the only way to go. If you wish to control airspace with impunity. Lot less is required just to defend your own with credibility.

My guess is that F35 is going to see new more stealthy radar, new all aspect IRST, new RAM coatings better optimized against IR emission. Some engine tweaks are going to happen to later models.

Then at some point (decided by everybody else) it comes obvious that F35 is going to run into some other stealth aircraft and get mutual kill. Some active protection system adopted from tanks, but no matter how successful that is, some startstreak type "I'll throw tungsten rods at you as soon as I detect that shotgun blast".

https://en.wikipedia.org/wiki/Starstreak_(missile)

Missiles already travel at speed of mach 3, which is same that autocannon shells. Maybe you could also (finally) get some use for metal storm concept, and implement five round burst cannon inside AA missile. (That kind of cannon can get significant weight reduction once you don't need to worry about fatigue and safety factors to keep close by personnel safe.)

The final nail in the coffin is engines. F35 engines have very good thrust/weigh, but they have poor fuel economy. This allows big weapons load for quick short mission. But if we accept that you can't after-burn, you don't need to turn that fast, and you won't survive to shoot more than 4 missiles etc, then your top priority is low fuel usage, long loiter and long range. Back to the missileer concept.

The problem with F22 and F35 is exactly their success. They are the first prototypes of the stealth/missile age. I'm expecting bit similar situation than with first swept wing afterburning planes. Those things got outdated in a decade. But if China implodes, then everything slows down.

> As soon as someone learns to detect F35 radar signal, more than half if it's stealth advantage melts away.

Much of the stealth advantage of any aircraft evaporates as soon as it turns on its radar. It's not a matter of "learning to detect" anything. An aircraft that wants to be stealthy runs with radar off and relies on passive sensors. A system like this, if it could be made to work at the scale of a fighter radar, would change that.

> F35 sales pitches are probably warming up right now, so news like this are expected.

Scaling this system up to the range and power required for a fighter radar is going to be a lot of work.

> The only surprise for me is that this comes from the army and not the air force or navy. They probably need to worry about enemy droids. And if they worry about those droids using radar, they need to worry about enemy anti-radiation missiles.

I will hazard a guess that this effort grew out of the artist formerly known as Future Combat Systems. Part of the effort was the Multi-Function Radar Frequency System (MFRFS, pronounced "merrfs") which was a vehicle-mounted scan-and-warn radar that would have been part of a larger active protection system. The idea was to identify incoming ordinance, particularly RPGs, and 1) identify the shooter's location; 2) identify the specific target vehicle and warn the crew; 3) trigger an active protection system, if equipped.

All of this predates drones, and the Army has been interested in small-scale radar for decades. The concern on detectability is to keep the enemy from identifying and tracking ground forces using systems like MFRFS by using the emissions from the sensors.

> This is probably part of larger picture of U.S. armed forces to avoid using Infra Red Search and Track (IRST). Because that makes stealth planes look bit silly, when you go past ~0,07m^2 radar cross section. At that point you would get parity with detection ranges of common radars and modern IRST sensors, which would be something like 80km for fighter jet sized object. But this would mean no operations in enemy airspace, as flight ceilings are typically around 20km. F35 has RCS 0,01 and F22 RCS 0,001 which is just great for operating in enemy airspace, if the enemy can't detect their radars and lacks IRST.

I have no idea where you are getting RCS numbers from, since those are classified.

As for IRST, I have no idea from where you got the idea that the US is ignoring it. The US Navy and Air Force have been mounting IRST sensors on their fighters since Vietnam. The F-22A and F-35 carry the very sensors you say the USAF is ignoring. Also, an IRST sensor can detect a fighter (ass-on) at 80km; it cannot identify or track that aircraft like a radar can. It needs to be much closer to do that.

> Currently it seems the best USAF can do about IRST is to pretend it doesn't matter. So if there is any coordination between the branches, the army has to get their own stealth radar against enemy drones. After two decades and gazillion dollars, we probably see subsonic F40-cool-skin, with reflecting mirror finish aluminum body, that eliminates this problem. And power projection and proceed uninhibited.

No, you won't. First off, the primary source of heat in an aircraft is the aircraft's own power plant, not solar heating. Second, a mirror finish would be a beautiful target for radar. It would be a blinding "KILL ME!" sign to even the most primitive systems. For that matter, so would a subsonic aircraft. Third, like I said, not modern air force is ignoring IRST.

> Right now we don't hear about this aluminum shit, because U.S. is still funding some weaponized lasers. Airborne lasers smelled like "overspending" before, but it's really going to smell like bluff when reflecting surfaces increase power requirements some 400%. They already suffer from bad power/weight ratios. But once naval laser "close-in weapon system" has been fielded (because any chance is a good one when you're desperate) we can go back to airplane design.

The airborne laser projects are intended to target ground vehicles and missiles, not aircraft. Naval CIWS is also intended primarily for targeting missiles. Current gun-based systems only have a range of ~2km, and no fighter pilot has been ballsy enough to come that close to an enemy ship in combat since the Argies bombed British landing ships at mast height in the Falklands.

> Sorry, this is bit long. I've had this autistic streak about this subject for past two weeks.

Yeah, so am I. I worked in it for almost a decade, though.

>No, you won't. First off, the primary source of heat in an aircraft is the aircraft's own power plant, not solar heating. Second, a mirror finish would be a beautiful target for radar. It would be a blinding "KILL ME!" sign to even the most primitive systems. For that matter, so would a subsonic aircraft. Third, like I said, not modern air force is ignoring IRST.

I just read few lengthy papers on that. Supersonic cruise causes so much skin friction that you can't gain in speed what you lose in detection distance. Future fighters are likely to be subsonic for this reason. The hot jet plume is surprisingly invisible, but hot engine parts do show from behind. Current detection relies mostly on skin friction and hot engine parts, but if you go even slower both drop to x^3. Then you need to worry about sun heating, etc, which some systems are already capable of detecting to pretty whopping ranges.

Mirror finish with faceted plates is practically Lockheed F-117 Nighthawk, withouth its RAM paint. That paint gives only part of it's stealth, it's maintenance heavy and typically optimized for relatively narrow band. So if that goes out of the window, you get bigger RF signature but smaller IR signature. Which sounds pretty good idea.

"Third, like I said, not modern air force is ignoring IRST."

Right? I mean, just consider the B-2 and F-117 exhausts and the amount of work done to reduce their thermal signatures.

Eurofighter and Superhornet first flew in mid 90's. Eurofighter has been shipped with PIRATE IRST since 2007. At the same time dudes started thinking about equipping Super Hornet with short range IRST. That option will be available some time this year. Maybe, or it will be delayed by two years.

U.S. is not ignoring IR spectrum completely. But it's pretty low priority compared to other players.

Infrared sensors aren't magic. Anything that fits on an airplane has a severely limited field of view and low resolution. Weather conditions can degrade it far more than radar. It may be able to give you bearing and azimuth to a target but you're not going to get accurate data on range, speed, or heading. It's not like radar where that data can be calculated from the return delay and Doppler shift. If you only see a blob of pixels it's pretty hard to distinguish between a nearby small airplane moving away versus a far away large airplane moving towards you.

That would be correct for ranges above 50km or for systems that we're first fielded in the 60's. With modern system at ranges below 50km you can get speed, identification and distance. But it all depends on weather, heat signature and contrast against backround.

For anything you can fit in a missile, that 50km is close to current max range of detection and we have all the problems you mention. But direction is all that missile needs for most of the flight time. Modern missiles have so good kinematic performance that they might begin to "lead the target" only one second before impact. At mach 3 thats about 1km.

Digital radio frequency jamming can hide size and distance from a radar too. The downside is that you need your own radar to send the masking signals. But it can't hide direction. https://en.wikipedia.org/wiki/Digital_radio_frequency_memory

Gripens Skyward-g IRST is said to weight about 60kg, which is light for such system. Gripen also has light weight radar, that weights 150kg. Other 4th gen figthers seem to sport 150kg IRST and 400kg radar. So you could theoretically replace the radar with 3 or 4 IRST, while not gaining any weight.

Does anyone know what non-traditional radar could mean?

It's "non-traditional radar waveform". They are referring to waveforms and modulation techniques not traditionally applied to radar signals. Radar typically has a very regular waveform. So regular, in fact, that a receiver can tell what type of radar is sending the signal by recording the overall signal pattern and deriving radar parameters from that (center frequencies, chirp bandwidths, scan patterns, and such). The type of obfuscation they are doing here is more typical of communications systems.

It looks like it combines features from pulse-Doppler radar and noise radar. It amplitude and phase modulates a complex pulse-linear FM waveform (linear chirp) using pseudo-noise.

I'm not familiar with this particular research. ACPN is not something US army just discovered. Agile beam, agile frequency, pulse compression and pseudo-noise waveforms are the direction military radars are going towards.

At a guess, it includes things like the tricks in

http://dtic.mil/dtic/tr/fulltext/u2/a456960.pdf ("DETECTION AND JAMMING LOW PROBABILITY OF INTERCEPT (LPI) RADARS")

but (1) it's obviously not a very precise term and (2) it would be surprising if all of the relevant techniques were available in an unclassified review from 2006.

Interesting progress; It's like CDMA for radar.

For those who have one hour available, check out this amazing talk about the early history of silicon valley, back when the first tech sector was radars for WWII: https://www.youtube.com/watch?v=ZTC_RxWN_xo

So this is spread-spectrum CDMA applied to a radar pulse?

My reading, based mainly on what they called it (Advanced Pulse Compression Noise), is no. I think what they are doing is adding an extra step that convolves the transmitted signal with a random noise signal before transmission, then deconvolves it when received as part of the normal convolution step in pulse compression.

They may also be randomly shifting the center frequency and chirp bandwidth in top of this. Frequency-hopping radar is not a new idea.

So direct sequence + frequency hopping? Interesting. Makes it hard to detect.

Sounds exactly like direct sequence to me. Pretty neat.

Nice! sounds like recent LIDAR innovations

https://youtu.be/30Jc0GpYKYI

But does it have a back door? Hopefully not "end to end" encryption, at least.

Please do not make posts like this.

Wow - what's with the downvotes?

IMHO what's good for the goose is good for the gander.

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