mingmar@cs.mcgill.ca (Ming MAR) (06/15/91)
In article <1991Jun14.143930.28999@eng.umd.edu> sdorsey@eng.umd.edu (Bill Dorsey) writes: >I'm working with some RAM (Radar Absorbing Material) here at work How does RAM work?
mingmar@cs.mcgill.ca (Ming MAR) (06/18/91)
In article <2003@ole.UUCP> ssave@ole.UUCP (Shailendra Save) writes: > HaHaHaHaHa!......... No, these things are not illegal, and I > am not laughing at that. The thing about having RAM is fine and > dandy, but as you will find out (just as I did) is that the > shape and size of those things are so funny, your car will look > like a chameleon with overgrown spikes. ... > I attended a seminar at Univ. of Michigan, and the Prof gave a > neat lecture about radar, and told us about how those things > worked, and what you can do about it. You'll notice that stealth aircraft don't look like chameleons with overgrown spikes. Do you have any idea how Radar Absorbing Materials work?
ssave@ole.UUCP (Shailendra Save) (06/18/91)
From article <1991Jun18.005130.28440@cs.mcgill.ca>, by mingmar@cs.mcgill.ca (Ming MAR): > In article <2003@ole.UUCP> ssave@ole.UUCP (Shailendra Save) writes: > > You'll notice that stealth aircraft don't look like chameleons with > overgrown spikes. Do you have any idea how Radar Absorbing Materials > work? Stealth does use a RAM for *reducing* detection by radar. However, what gives it the "stealth" ability is not that, but the fact that the aerodynamics of the planes on the aircraft are such that no radar is reflected back to the originator. Now, if the question was to make it radar proof by changing the shape of your car, then I agree it can be done. But if you expect to get immunity to radar using RAM, dream on. You will certainly get a reduced return from such cars, but as I pointed out, it takes only a windshield or a head-lamp lens to get an accurate enough reading of the vehicle speed. So let me ask you your question. Do you have any idea how Stealth aerodynamics work? Shailendra ssave@caen.engin.umich.edu sumax!ole.uucp!ssave
ssave@ole.UUCP (Shailendra Save) (06/20/91)
In article <1991Jun18.005130.28440@cs.mcgill.ca>, mingmar@cs.mcgill.ca (Ming MAR) writes: > You'll notice that stealth aircraft don't look like chameleons with > overgrown spikes. Do you have any idea how Radar Absorbing Materials > work? If RAM worked 100%, like you contend they do, how come Czechoslovakia has come out with a detection method which can detect the Stealth aircraft at 250 miles?
simich@oak.eecs.ucdavis.edu (Myron Simich) (06/20/91)
Somebody mentioned the 2 ft triangular absorber that is used in RAM. This is not the only kind that is available. I use a type of RAM that looks like a piece of vinal but is much heavier. The frequency range that it is used for is from 2 Ghz up to 26 Ghz. Cost is approx. $55/sq ft. Works well for what I need it for but I don't know how well it would work on a car. There is also another type that looks like black styrofoam (sp) but is flexible. I have used this type down around the 3 to 5 Ghz range. This type is much cheaper (I forget the exact price). Neither of them have the funny triangular look. Just to let everybody know. M.Simich
skeffing@motcid.UUCP (John F. Skeffington) (06/21/91)
In article <2017@ole.UUCP> ssave@ole.UUCP (Shailendra Save) writes: >In article <1991Jun18.005130.28440@cs.mcgill.ca>, mingmar@cs.mcgill.ca (Ming MAR) writes: >> You'll notice that stealth aircraft don't look like chameleons with >> overgrown spikes. Do you have any idea how Radar Absorbing Materials >> work? > > If RAM worked 100%, like you contend they do, how come > Czechoslovakia has come out with a detection method which can detect > the Stealth aircraft at 250 miles? Where have you heard about this new detection method? I do not recall any knowledgable person on stealth technology claiming the aircraft was invisiable to radar, rather it was difficult to detect. The implication of being able to detect a stealth aircraft at 250 miles woufd be that it could detect a "normal" aircraft at several times that distance. I find this very interesting and would like to know more about it. John Skeffington
joel@cfctech.cfc.com (Joel Lessenberry) (06/22/91)
In article <7372@celery15.UUCP> skeffing@motcid.UUCP (John F. Skeffington) writes: >In article <2017@ole.UUCP> ssave@ole.UUCP (Shailendra Save) writes: >>In article <1991Jun18.005130.28440@cs.mcgill.ca>, mingmar@cs.mcgill.ca (Ming MAR) writes: >> If RAM worked 100%, like you contend they do, how come >> Czechoslovakia has come out with a detection method which can detect >> the Stealth aircraft at 250 miles? > >Where have you heard about this new detection method? I do not recall >any knowledgable person on stealth technology claiming the aircraft was >invisiable to radar, rather it was difficult to detect. The implication >of being able to detect a stealth aircraft at 250 miles woufd be that >it could detect a "normal" aircraft at several times that distance. I >find this very interesting and would like to know more about it. > The radars which can detect the stealth fighter are in fact mostly older, long wavelength systems. Some of these systems are classed as Over The Horizen systems, because they give some coverage past line of site. The long wavelengh, low frequency can be bounced by the upper atmosphere. However, the spatial accuracy of a radar coorespondes to frequency. The higher the freq. the greater the accuracy. I have heard that while detectable, you only know that the aircraft is ... over that away.... joel Joel Lessenberry, Distributed Systems | +1 313 948 3342 joel@cfctech.UUCP | Chrysler Financial Corp. joel%cfctech.uucp@mailgw.cc.umich.edu | MIS, Technical Services {sharkey|mailrus}!cfctech!joel | 2777 Franklin, Sfld, MI
tedwards@aplcomm.JHUAPL.EDU (Edwards Thomas G S1A x8297) (06/22/91)
In article <7372@celery15.UUCP> skeffing@motcid.UUCP (John F. Skeffington) writes: >In article <2017@ole.UUCP> ssave@ole.UUCP (Shailendra Save) writes: >> If RAM worked 100%, like you contend they do, how come >> Czechoslovakia has come out with a detection method which can detect >> the Stealth aircraft at 250 miles? >Where have you heard about this new detection method? I do not recall >any knowledgable person on stealth technology claiming the aircraft was >invisiable to radar, rather it was difficult to detect. The implication >of being able to detect a stealth aircraft at 250 miles woufd be that >it could detect a "normal" aircraft at several times that distance. I >find this very interesting and would like to know more about it. Not actually. RAM does a fine job of attenuating reflection of radio transmissions over a range of frequencies. For a single frequency radar operating within the reflection attenuation band of the RAM, it will be very difficult to detect it. However, it is possible to implement a "chirped" radar system or a multiple xmitter radar site which is capable of integrating reflection information over a large range of frequencies to bring a stealth aricraft signal out of the noise. The moral of the story is that while the U.S.S.R. might be capable of producing anti-stealth radar (assuming they can get enough info on the stealth aircrafts to do proper testing of the system), a small country with less technical knowledge and money would find this much more difficult. The radar sets required to detect it will be more complex and expensive than normal radar systems (and being more complex may make it more prone to failure). Also radar xmitters trying to detect stealth aircraft will be easily identifiable, and it may be difficult to implement a stealth-proof radar system which can fit into a fighter. Any defense one can build will be an easy target for someone else's offense... -Tom
hermann@cpsc.ucalgary.ca (hermann) (06/22/91)
In article <7372@celery15.UUCP> skeffing@motcid.UUCP (John F. Skeffington) writes: ... The implication of being able to detect a stealth aircraft at 250 miles woufd be that it could detect a "normal" aircraft at several times that distance. I find this very interesting and would like to know more about it. I believe that those large (drivein theatre screen-sized) phased array radars you see in some of the journals from time to time use "back-scattering". To my understanding backscattering bounces signals off the upper layers of atmosphere to "see" over the horizon. Added benefit is looking "down" on your target, negating the effect of head-on countermeasures (stealth aircraft emphasize reducing the "head-on" radar signature). I have heard that large coastal phased arrays were used in the eastern block for a few years before the west started using them. | Mike Hermann | hermann@cpsc.ucalgary.ca _Organized_ religion is like organized crime: it preys on people's weakness, generates huge profits, and is nearly impossible to eradicate.
mingmar@cs.mcgill.ca (Ming MAR) (06/24/91)
In article <2005@ole.UUCP> ssave@ole.UUCP (Shailendra Save) writes: > Stealth does use a RAM for *reducing* detection by radar. No argument from me. In article <2005@ole.UUCP> ssave@ole.UUCP (Shailendra Save) writes: >From article <1991Jun18.005130.28440@cs.mcgill.ca>, by mingmar@cs.mcgill.ca (Ming MAR): >> Do you have any idea how Radar Absorbing Materials >> work? I had posted a follow-up article asking the originator of this thread (Bill Dorsey) to explain how radar absorbing materials work. I didn't get a response. I later asked you but since you gave no explanation, I'll assume you have no idea how radar absorbing materials work. Thus far, I haven't seen anyone in this newsgroup explain how it works. Can anyone here explain how radar absorbing materials work? > the aerodynamics of the planes on the aircraft are such that no > radar is reflected back to the originator. Radar cross-section is reduced but not eliminated. Generally speaking, I'm not disagreeing -- merely quibbling. > it takes > only a windshield or a head-lamp lens to get an accurate enough > reading of the vehicle speed. Are you saying that the windshield glass reflects radar back to the gun? > So let me ask you your question. Do you have any idea how Stealth > aerodynamics work? You started your article on that very topic, so... if I didn't know before, I know now. I'm not exactly sure what you mean by "stealth aerodynamics." I am an aerodynamicist. I received my Master of Engineering from the University of Toronto Institute for Aerospace Studies in 1977. You tell me what you mean by "stealth aerodynamics" and I'll tell you if I know anything about it. That part of the discussion can be conducted in sci.aeronautics. Now, getting back on track, yes, I am aware of the technique of redirecting reflections away from the illuminator. What I don't know is how Radar Absorbing Materials work. (I have my own ideas, but I'd like to know for sure.) You said that you took a course in radar technology and said that a stealthy car would look like a bumpy chameleon. I assume you mean the type of pyramids one finds in an anechoic chamber. I said that stealthy cars don't have to look like that and gave aircraft as examples of non-bumpy vehicles. I hadn't intended to answer your article, but then you posted another one <2017@ole.UUCP> wherein you said: > If RAM worked 100%, like you contend they do, how come > Czechoslovakia has come out with a detection method which can > detect the Stealth aircraft at 250 miles? I have never implicitely or explicitely contend that RAM reduces radar cross-section to zero. If that is the _only_ point you wish to make, then fine, we are not in disagreement. I haven't heard of any breakthroughs from Czechoslovakia. Perhaps you could supply details? A couple of people in this newsgroup, Mike Hermann and Joel Lessenberry, suggested Over-The-Horizon-Backscatter as a surveillance tool. Tom Edwards suggested Ultra Wide Bandwidth, presumably for target acquisition. Apparently, noone else has heard anything about Czechoslovakia. Last year, there were reports out of Saudi Arabia about radar detection of F-117's. For your edification, I include below my translation of an article about it. Remember, the article was written before the F-117 was able to prove itself in the war. From "L'Express International" 21 September 1990 (the Stealth Fighter sighted issue): On cover: "Gulf: The American invisible airplane detected by French radar" On page 19: Exclusive The radar that snared the stealth airplane Nasty surprise for the Americans: the Saudi Shahine system, contructed by Thomson, detects the F-117A. And obliges them to reconsider their device. The American stealth plane F-117A was spotted several times by the French radar of the Shahine ground-to-air missile system in Saudi Arabia. This information, gathered last week from sources close to the Saudi army, puts into question the American device deployed in that country. To shelter them from a possible detection by the Iraqis, the commander of the U.S. Air Force has immediately transfered the bombers of this type to a base in the southwest of the Saudi kingdom, next to the Red Sea, near Yemen. The F-117A, the latest in American technology, was designed "for penetration in a high threat density environment and for attacking high strategic value targets." The unsuspected performance of the radar which equipes the Shahine missile batteries, constructed by Thomson-CSF for Saudi Arabia, were obtained during flights of the bomber near the sites where the anti-air defense system is installed. The pulse-Doppler surveillance radar thus came to snare, several times, the invisible plane at a distance of about 17 kilometers. The computer was able to integrate sufficiently the characteristics as to establish an actual signature of the F-117A, this permits the system to recognize immediately the target. The probability of destruction of a target by the Shahine is 90% with one missile and 99% in the case of a simultaneous firing of two missiles. The stealth plane, of which the principal characteristics are very angular forms and a special radar signature reducing covering, is on the other hand lacking in aerodynamic qualities and manageability. Its speed is no faster than "high subsonic," it peaks at 900 km/h. Spotted by radar, the F-117A has nothing but its jamming system and chaff to try to escape the missiles. Entered into service in October 1983, this airplane has been put to the test on numerous radar systems. With success. And even if its bombing capability, tested in the month of December 1989 in Panama, was revealed as mediocre, the program was considered a success. It seems that, aside from the intrinsic capability of the Shahine, the clean conditions in Saudi Arabia favored the spotting of the F-117A -- far horizon, heat and reverberation, diffusion of electromagnetic waves. What ever the cause, its detection by radar, whatever the reason, puts into question the very design of the aircraft -- its developement and construction of 59 copies will cost a total of $6.5 billion. It is a contract of $4 billion that Thomson-CSF, prime contractor -- with Giat (Groupement industriel des armements terrestres) and Matra -- signed in 1984 with Saudi Arabia for the delivery of an anti-air defense system baptized Shahine, "Falcon Eye." The Shahine, developed exclusively for Riyad starting from Crotale missiles, today find themselves on the front lines of defense of the Saudi kingdom. This position explains the discretion of Thomson-CSF concerning the performance of its equipment. The electronic systems division, contacted by L'Express, refuses all comments. "We wish to neither confirm nor deny this performance. Several Thomson employees are on the other side with the French and foreign hostages, and we can't say anything while they're in Iraq." They add that the Saudi clients don't like superfluous comments. A certain number of Thomson-CSF employees are in Iraq, posted for the maintenance of the radar system sold to Iraq and of its mobile version installed on board Ilyushin aircraft. Do the Iraqis also have the means to detect the F-117A? They are equiped with a French anti-air system, the Roland, manufactured by Euromissile. The Iraqis today possess 14 AMX-30 tanks equiped with Roland and have at their disposal 133 Roland 1 and Roland 2 launch sites. Their arsenal has grown to 2,780 missiles, whose performance is however inferior to that of the Shahine. Besides, in order for the Iraqi system to come to discover the F-117A signature, the radar has to identify it several times. It is unlikely that the Americans will give them that opportunity. Nevertheless, it is likely, sooner or later, that other radar will be able to, like Shahine, identify the F-117A, constraining the expensive stealthy bomber to a brief carreer. -- <by> Jean-Michel Caradec'h And, for what it's worth, I remember reading in _Aviation_Week_ that an American anti-aircraft radar failed to lock-on an F-117 even after visual sighting. Aviation Week also had an issue concentrating on anti-stealth technology.
mingmar@cs.mcgill.ca (Ming MAR) (06/24/91)
In article <9207@ucdavis.ucdavis.edu> simich@oak.eecs.ucdavis.edu (Myron Simich) writes: > I use a type of RAM that looks like a piece of vinal but is much > heavier. .... There is also another type that looks like black > styrofoam (sp) but is flexible. Do you know how this stuff works? Do you know if this is the same stuff used on aircraft?
ssave@ole.UUCP (Shailendra Save) (06/24/91)
From article <1991Jun24.055534.24442@cs.mcgill.ca>, by mingmar@cs.mcgill.ca (Ming MAR): [A real nice and well compiled article deleted] The only point I am trying to make, is that no matter what you put on your car for RAM, there is enough cross-section of non-RAM material left on it to give a good radar reading. You can't radar-proof it using RAM. You will definitely reduce the chances of getting detected, (since the radar system will only register the largest echo) and give you more time to slow down. Now, if you were planning to bomb/shoot/destroy the police car in question, you would definately be more successful than if didn't have RAM. This, incidently, is the principle of operation of the Stealth aircraft. Conventional aircraft radar *can* detect the Stealth at 37 miles, as opposed to normal aircraft at about 250-300 miles. Talking about the chameleon type spikes, yes, I was talking about the chamber material. It combines RAM with obtuse angle deflection. About the Chez's new radar, I don't have any details, only what they talked on BBC and later on NPR. Thank you for a nice article, and taking so much time to type it in. Shailendra ssave@caen.engin.umich.edu sumax!ole.uucp!ssave
pierson@ggone.enet.dec.com (Dave Pierson) (06/25/91)
In article <1991Jun24.055534.24442@cs.mcgill.ca>, mingmar@cs.mcgill.ca (Ming MAR) writes... >I had posted a follow-up article asking the originator of this >thread (Bill Dorsey) to explain how radar absorbing materials >work. I didn't get a response. From the published information, and EMI work (including anechoic chambers), consider a nonconductor, (glass, ceramic, plastic, loaded with carbon (lossy conductor) or ferrite. Efectivenss will vary with thickness, wavelength of threat. For a fixed threat frequency (police radar) a fixed thickness should do. IF the elements providing the return ar properly identified and suppressed. >Last year, there were reports out of Saudi Arabia about radar >detection of F-117's. For your edification, I include below my >translation of an article about it. Remember, the article was >written before the F-117 was able to prove itself in the war. Thanks. I can think of some questions to ask but.... thanks dave pierson |the facts, as accurately as i can manage, Digital Equipment Corporation |the opinions, my own. 600 Nickerson Rd Marlboro, Mass 01752 pierson@cimnet.enet.dec.com "He has read everything, and, to his credit, written nothing." A J Raffles
simnet@ssc-vax.UUCP (Mark R Poulson) (06/25/91)
> >> If RAM worked 100%, like you contend they do, how come > >> Czechoslovakia has come out with a detection method which can detect > >> the Stealth aircraft at 250 miles? The version of this story I heard was that they detected the "emissions that were necessary for an aircraft to fly at low altitudes". I have no idea which emissions they were referring to (or even if the press got it correct), and whether these emissions would be "on" in wartime or not. Anyway, the story didn't say anything about detecting the stealth plane with RADAR. Mark
simich@elm.eecs.ucdavis.edu (Myron Simich) (06/26/91)
As I understand it, and I have not made any real effort to explore the nitty gritty as to how it is done, the material acts as an attenuator at microwave frequencies. As a microwave signal impacts upon this type of material and penetrates into it, the signal is dramatically attenuated. This means that real part of the propagation coefficient gamma is real. For any real part of gamma greater than zero there is an expnential decay of a wave in the material. Of course the material should have an impedance such that the majority of the wave is absorbed into the material and not reflected. I assume that this has been taken into account (the material works quite well in the research that I have been doing so it would seem that this is the case). As far as I know, this is not the same material user in stealth aircraft. I believe that they use some sort of carbon fiber material but I am not sure. Again, let me state that this is *my* understanding of how the material works. I don't claim that this is *exactly* the way it works, just my understanding of how it works. Myron Simich Simich@iris.eecs.ucdavis.edu
wiml@milton.u.washington.edu (William Lewis) (06/28/91)
In article <4189@ssc-bee.ssc-vax.UUCP> simnet@ssc-vax.UUCP (Mark R Poulson) writes: >The version of this story I heard was that they detected the "emissions that >were necessary for an aircraft to fly at low altitudes". I have no idea which >emissions they were referring to (or even if the press got it correct), and >whether these emissions would be "on" in wartime or not. Perhaps they were referring to the IR signature. The engine exhaust is significantly hotter than the surrounding air, and so emits infrared radiation that can presumably be detected. It would be pretty hard to turn this "off", though I bet people are trying ... Someone else pointed out in this newsgroup that the bow wave (shock wave for supersonic craft?) is detectable by radar. -- wiml@milton.acs.washington.edu Seattle, Washington (William Lewis) | 47 41' 15" N 122 42' 58" W "Just remember, wherever you go ... you're stuck there."