New Radar Techniques Make U.S. Stealth Bombers/Fighters Visible?

Factual Questions
1

According to a lead article by the AP:

"America’s stealth bombers may be in danger of having their cover blown by a new type of radar that uses cell phone technology, researchers say.

The Air Force says the problem is limited and America’s stealth fleet is in no danger. Yet U.S. intelligence reports label the radar a serious threat, and several scientists say they agree."

If this is true, what can the U.S. do to counteract this new type of radar and preserve our military edge? Does this make the JSF obsolete before deployment?

Obliterating transmission towers prior to a raid as a preventive measure would seem to tip our hat rather obviously.

Let’s keep this factual and out of IMHO, please.

2

Stealth aircraft use a number of technologies to reduce their radar signature. Non-reflective coatings/materials, baffles, curved surfaces, absence of protrusions, etc. No one new detection technology will overcome all these in one fell swoop. So the AP headline may be slightly hyperbolic.

FWIW, stealthy aircraft are still visible to radar. It’s just that the size of the return echo is so small that their detectable range is too limited to be useful.

Also, obliterating transmission towers is already an established tactic. Before we had stealth aircraft we would use jamming aircraft to mask the incoming strike against the enemy’s radar installations. It’s still one of the riskiest parts of an attack.

3

I heard this report on the radio a few days ago. There’s a report here (which I think needs to be taken with a pinch of salt, there’s something not quite right about it IMO), including the suggestion that the stealth bomber lost over Serbia may have been located with this system (although there doesn’t seem to be any evidence for this).

4

Well, the nuts and bolts of the system got immediately classified, so there’s really only rumor and guesswork as to how it actually works.

That having been said, from my admittedly very limited knowledge of microwave transmission and detection, I have a couple of ideas how it might work.

A) The system actually detects “void” areas. Instead of sending a search-radar beam out and getting a reflected signal, the cell array makes note of “empty” areas, where there should be signal, but there isn’t.

If Tom Clancy can be believed, some of our modern submarines suffer the same problem- they’re actually quieter than the surrounding random noise of the ocean, and so can be located (roughly) by looking for small, localized quiet zones.

B) The cell arrays are so sensitive, they can detect even the tiny fraction of reflected energy.

Or C) The arrays are just that, arrays. “Stealth” technology doesn’t necessarily “absorb” all the microwave energy, most of it is simply reflected away from the point source. With a widely-seperated array, other cells can detect the energy reflected from different directions

Point-source search radars have the emitter and detector at the same- or nearly so- location, so the stealth has to reflect the energy off to the side, or above and below. But with an array, there’s additional “detectors” off in the directions the energy is being reflected to.

Personally, I think it’s a factor of the last two. The cell receptors are typically dealing with fractional-milliwatt signals, so they have to be pretty sensitive to keep a good voice signal. (Which is surely a more complex signal than simply a mere reflected fixed pulse-rate signal from a search-radar.) And second, the arrays are wide-set, heavily interconnected and designed to share and transfer signals as the user moves from cell to cell.

It’s actually a brilliant idea. How long before the FAA starts leasing air-time from the Baby Bells to augment their 60’s era traffic-control radars? :smiley:

5

There is no mystery to this technology. It has long been known that stealth aircraft present almost no return signal to the radar site that illuminates it, but that they DO present a return signal to some OTHER location than the origin of the radar signal. So all you have to do is network your radar systems. When site A sends a pulse, sites B, C and D listen for the return. Add some fancy computer analysis and you have located the plane. All the cellular gadget system does is provide a large amount of illumination of the plane from many angles, and a large amount of receivers networked together to detect backscatter from the planes.

6

Supposedly, the Russians developed an “anti-stealth” radar system several years ago. They sold a few to the Serbs, who used them to shoot down that F-117 during the Balkan War.

7

Boy, the Romulans aren’t going to be happy about this…

8

When I first moved here to the Czech Republic, they were talking about this. The Czechs (supposedly) came up with the (or a) system that worked on the ‘less noise’ concept. This was back in 1997. I can’t look for a cite right now, but I remember talking with friends about it.

-Tcat

9

The “anti-stealth” radar was nothing more than a slightly modified, older system that the Russians were no longer using in front line service. What makes it dangerous is that it uses longer wavelengths, which the steath technology wasn’t designed to deal with. Basically, the wider the the bandwidth stealth technology is designed to defeat, the more expensive and difficult it becomes to design and build. The F-117 took a look at the most common threats (short-wavelength radar) from the supposed most likely enemy (USSR), and designed to defeat that. The folks at the Skunk Works never expected the USSR to collapse, nor did they expect to be facing obsolescent radars in low-intensity conflict, so they never designed for it. Now, of course, everyone around the globe will be buying or designing long wave radars, and slapping modern signal processing electronics on them.

Turn, and turn about: It’s a constant contest between offense and defense, detection and steath. Right now, detection has gained some small ground, but the designers, now alerted to the vulnerability, will be hard at work, looking for a new counter-measure. The game goes on.

10

The system mentioned works but it requires a fairly dense network of cell phone towers. Currently cell phone towers are only located in in dense metropolitan areas and along major hiways. Most poor countries such as serbia do not have nearly the density needed for this to work.

11

When I first read about Stealth Technology, it seemed clear to me that it only minimized retroreflection of the radar waves. (It’s very easy to make a radio retroreflector – any interior corner structure will do it. See a book on radar or read Heinlein’s The Rolling Stones). So it seemed obvious that you could defeat stealth technology if you decouple your radio source and your detector, putting them long distances apart. If I understand the current system correctly, it makes use of existing radio and microwave sources elsewhere in connection with a radar receiver. But there’s absolutely no reason that a determined opponent couldn’t build there own broadcast towers to be used in conjunction with a sepsarate receiver. I’m just surprised it all took this long to come out in the open.

12

This isn’t especially a new topic, actually. There was discussion on this at least a year ago, that I recall. A search on Slashdot.org might be useful.

The point of the matter is that it requires a large infrastructure that can not be easily hidden. Certainly, it is possible to build this, but only countries that have large cell-phone networks will have them ready-made.
This means that the people who are currently most likely to find themselves in conflict with the US must make a large investment in a antenna and computer setup that will be blown at start of hostitilites, or stealth aircraft will be as stealthy as ever. It might even make themselves greater targets, by marking militarily significant areas with a forest of cell towers.
Add to this the fact that this radar complex will not transmit targeting data to a weapons system after launch, or a flying fighter, without an additional, and easily jammed communications channel and you have the interesting point of possibly knowing exactly, more or less, where the fighter is, and not being able to hit it with anything.

13

Yes, you need a lot of infrastructure to make this work. That’s not necessarily a difficulty, though: In China, for instance, wireless phones are cheaper than landlines, because they don’t already have the landline infrastructure like the US does. Even without a military application, China is being covered with cell towers.

14

Does any body has more info on what cell phone technology is used? I don’t think they can just tap into the cell phone towers.

15

The technology is called “passive” radar, because it relies on detecting anomolies in a background radio frequency illumination. The idea is that with enough transmitters, you can provide an ambient background illumination of radio waves, which a radar-aborbing object will cause a change in the signals picked up by scattered receivers. In fact, Spoofe’s quip about the Romulans is apt because it’s exactly like the “tachyon grid” that’s been featured in a few of the shows. A visual light analogy:

Conventional Radar: It’s a pitch-black moonless overcast night. You turn on a searchlight to try to spot someone. If they’re wearing matt-black clothing like a ninja, they’re going to be pretty hard to spot.

Passive Radar: You have a baseball field lit up for a nighttime game with lots of lights. You can easily spot someone; if they’re wearing light-absorbing clothes, they just show up as a black spot.

Drawbacks: You need a fairly dense network of transmitters and receivers to cover a given area, and sophisticated signal processing software to translate the data into a fix on an aircraft.

To remain stealthy in such an environment, an aircraft would actually have to transmit a signal to try to duplicate the radar waves that would otherwise be passing through it; like wearing a “hologram suit” for invisibility. Needless to say, that’s going to be difficult to achieve.

Note: I don’t think they’re talking about actually having cell-phone transmitters doing double duty as part of such a system (although that might be possible); it was just an analogy.

16

http://www.telegraph.co.uk:80/et?ac=005319116709487&rtmo=lzlFSAHt&atmo=rrrrrrrq&pg=/et/01/6/11/nbom11.html

I went to find the article posted by andy. His link did not work but goto http://www.telegraph.co.uk:80 and search for stealth. Those stealth links are hard to spot on a casual read through.

The article basically said that you setup a bunch of antennas about a football feild worth and watch how your reception of other peoples cell phone calls changes do a lot of math and find the planes.

So it sounds like the cell phone towers are the lights in Lumpy’s analogy.

17

I’m curious, because I don’t understand exactly what’s been said, about long wavelength radar. With velocity a constant (i.e., both signals promulgated in the same medium), a longer wavelength signal will have a lower frequency content. It would seem that instituting such a system where a shorter wavelength system had been in place would have to decrease resolution, as it does in other remote imaging methodologies.

So, I’m at a loss as to how that would aid in detection.

All the rest that’s been said, particularly with respect to receiver arrays and and passive (and/or source-independent) receivers, I understand and they make sense - in fact that’s the guts of what I surmised when I saw that wire story. My daily working world shifted from the use of 2D seismic data to 3D in the past decade, and expanded source and receiver arrays are (most of) the story there. I’m comfy with that.

But the long period radar part is something I didn’t grasp.

18

It does reduce resolution, which is why it’s not considered frontline equipment anymore. However, just because it’s lower resolution, doesn’t mean it’s not useful. With the application of improved signal processing, the resolution issue isn’t all that significant. Witness the F-117 shot down over the Czeck Republic as an example of “old” not being “useless”.

The reason longer wavelengths work is based on the principles of Radar Absorbant Material (RAM). Without going into classified detail, RAM is designed to absorb and attenuate electromagnetic radiation, either by trapping it, redirecting it, or by converting it to a different form (such as heat). RAM can only absorb a limited range of wavelengths and still be functional to design, build, and maintain within practical limits. The wider the range, the heavier and more complex RAM becomes. So, the designers target the range of expected threats, and design to that. With SovBloc armies, that threat was modern short wavelength radar. RAM and other stealth technologies are still effective to some degree outside their design parameters, but with sufficiently sensitive recievers, and good signal processing, a little can be enough.

Also, remeber that “stealth” is actually more accurately labeled “low observable technology”. Even within the design parameters, stealth aircraft still return some small amount of radar energy. The trick is to keep that energy return below detectable levels.

19

The thing is, if we really got into a war, all we would have to do is send in a bunch of F 117’s (YOU try tracking something that moves over 3.5 times it’s length a second with passive radar) armed with HARM missiles. Goodbye cellphone towers.

20

Stealth planes have always been detectable by radar. The problem is that you get a lot of false signals [noise] and reflections from things like birds, rain, sandstorms, etc. Since the people who put the radar in want it to be able to see, they filter this stuff out along with the small signal from stealth planes. All you need to detect stealth planes with existing radar is to upgrade the computing power to smart filter the signal. This is easier to say in the newspaper or in a book than it is to actually do it. But you can be sure some governments either have it or are working on it.

The “new” cell phone tower approach will also require a huge amount of computing. Think about how this would work. The stealth plane does not block out reception at the cell tower, it only changes it slightly. You need a central location, with a huge computer, to take real time feed from EACH cell tower. The computer has to see everything that each tower sees. You have to get all of these signals to the computer. If you do it by cell phone, then the signal will degrade, so you will need it sent over land lines. The computer can analyze all of the signals to look for a pattern of signal disturbance.

There is no one signal from one tower that proves there is a stealth plane. You look for a slight signal from one tower and an even slighter signal from the towers on either side of it, then a slight signal from the next tower which occurs at a later time corresponding to a plane’s speed, and so forth.

Or as others have mentioned, you could look for a series of exploding towers. This saves the cost of a new radar system and works with existing technology.

Think of it like the missle defense system the US is working on. The newspapers show the pretty sketches of how it works [like they did for the new radar]. But no one believes it is even close to a workable system.