
U.S. army developing encrypted radar waveform - chewymouse
https://thestack.com/world/2016/03/16/u-s-army-developing-encrypted-radar-waveform/
======
nradov
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.

~~~
hatsunearu
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](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.

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

UWB radar is also a thing.

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rocky1138
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.

~~~
dogma1138
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.

~~~
giardini
_" 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).

~~~
vonmoltke
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.

~~~
giardini
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."

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__mbm__
This relates closely to the [Darpa Spectrum
Challenge]([http://archive.darpa.mil/spectrumchallenge/](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.

~~~
lsaferite
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.

------
vlehto
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](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.

~~~
vonmoltke
> 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.

~~~
termain
"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.

~~~
vlehto
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.

------
dfc
Does anyone know what non-traditional radar could mean?

~~~
vonmoltke
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.

------
ivan_ah
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](https://www.youtube.com/watch?v=ZTC_RxWN_xo)

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

~~~
vonmoltke
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.

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

~~~
wrigby
Sounds exactly like direct sequence to me. Pretty neat.

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kylehotchkiss
Nice! sounds like recent LIDAR innovations

[https://youtu.be/30Jc0GpYKYI](https://youtu.be/30Jc0GpYKYI)

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

/s

~~~
dfc
Please do not make posts like this.

~~~
TallGuyShort
Please do not make posts like this.

