A question for radar/rf engineers - Page 1
Forum section: electronics / beginners

author: MrOmnos
author_rank: Frequent Contributor
timestamp: September 24, 2016, 08:43:33 pm
content: When they say B2 spirit has RCS of 0.001 m2or F-22 Raptor has a RCS of 0.001, are these numbers valid for certain band radar or does it mean it will have the same RCS for any kind if EM radiation? What does having small RCS mean for an aircraft? Does it mean it can't be detected at all? Or does it mean, you can detect it but the RCS is so small, you can't home your missiles on it? I suspect it means, it can't be detected at all, else enemy would scramble jets.

author: MrOmnos
author_rank: Frequent Contributor
timestamp: September 24, 2016, 09:48:54 pm
content: Quote from: evb149 on September 24, 2016, 09:20:22 pmThanks for the answer:I was doing some research on aircrafts in current military service all around the world and ones that will be coming in near future. "Stealth" has become keyword in every countries aircraft development program it seems. The whole F-35 program has been really expensive and when you look at the specs it is no better/similar to F-16s it is suppose to replace except for the part that it has small radar cross-section. In fact it is far behind in agility to russian Sukhois. That means almost all of the money went into making it stealthy . So, if Uncle Sam has invested so much trust in stealth technology, there must be something that his enemies hate about it.

author: Voodoo 6
author_rank: Regular Contributor
timestamp: September 24, 2016, 09:58:47 pm
content: This article will probably answer a lot of your questions about radar cross sections and the methods used: From Air Power Australiahttp://www.ausairpower.net/APA-2011-03.htmlWe have a Ratscat facility at the White Sands Missile range here.

author: MrOmnos
author_rank: Frequent Contributor
timestamp: September 24, 2016, 10:13:38 pm
content: Quote from: Voodoo 6 on September 24, 2016, 09:58:47 pmJust opened the post and saw pictures of j-20 and I saw j-20 pics back in 2014 and the first thin that cam to my mind was, who the hell sold raptor designs to Chinese? Lockheed was clearly hacked.

author: Voodoo 6
author_rank: Regular Contributor
timestamp: September 24, 2016, 10:27:52 pm
content: You might recall the 1999 shoot down of an American F117a in Yugoslavia, using an Sa-3 Goa air defense system. Stealth doesn't make it impossible just makes its a bit more difficult. Although, there might have been some hacks there is really no need to. The US defense industry is riddled with foreign agents from many nations.

author: elgonzo
author_rank: Unknown
timestamp: September 24, 2016, 10:37:45 pm
content: Quote from: MrOmnos on September 24, 2016, 10:13:38 pmThe J-20 has canards and no rear elevators, whereas the F-22 has rear elevators but no canards. Basically, the aerodynamic design of the J-20 is entirely different from the F-22.There is certainly a striking similarity in the general form of the fuselage, air inlets, canopy and such. It really is too close to be mere coincidence...

author: MrOmnos
author_rank: Frequent Contributor
timestamp: September 24, 2016, 11:04:40 pm
content: Quote from: Voodoo 6 on September 24, 2016, 10:27:52 pmActually, that's one of the reasons I asked this question, it was detected using Russian made VHF radar.(it still used vacuum tubes) The guy who shot it down said, he was able to detect the aircraft but SAM radars couldn't lock on. But when the pilot opened the bomb bay doors, SAMs obtained a lock and 3 missiles were fired. F-117 were clearly vulnerable to VHF. So yeah, a VHF radar with giant Yagi antennas and receiver made out of tubes, helped bring down one of the most advanced bombers ever made.

author: Voodoo 6
author_rank: Regular Contributor
timestamp: September 24, 2016, 11:29:33 pm
content: The SA-3 Goa has made some pretty impressive hits considering it was introduced in 1961. Russian weapon designers are at the top of the game. Veniamin Yefremov (Deceased) , general designer of Almaz-Antei, is one of the super gurus when it came to systems design.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: September 25, 2016, 02:51:25 am
content: My understanding is that "stealth" aircraft are optimized for low observability at X-band (~10 GHz) since that's the band used by most airborne fighter aircraft's targeting radar. They may also optimize for S-band (~3 GHz) from low elevations, since that's the band that's most commonly used for ground-based surveillance radars (that are part of a weapon system - longer range ground radars often use L-band instead).Given this, it wasn't terribly surprising that the S-125 Pechora could detect an F-117. It also reportedly did so at close range. I found it a bit more impressive that one of these systems shot down a Predator, which would likely have an even smaller RCS, and likely be optimized for low observability to ground radar.Radar bands are not merely bragging points (as in, "check out my pimped-out fighter with a Ka-band radar"), they're designed to a purpose. For example, radars that look for much lower RCS targets (ICBM RVs) are typically UHF or lower (GBR and TPY-2 are notable exceptions), since they tend to not be as limited by propagation losses. They are also ground-based, and are hence not size-limited.

author: Voodoo 6
author_rank: Regular Contributor
timestamp: September 25, 2016, 03:06:17 am
content: Have to agree in everything Radar said, not to mention the integration of multiple bands on a single platform. like the x-aesa - l-aesa ect. As long as you can cool the elements, the sky is the limit so to speak.

author: zl2wrw
author_rank: Regular Contributor
timestamp: September 25, 2016, 03:55:57 am
content: At short wavelengths (X, K, etc bands) it is practical to produce a tight beam from a small antenna (the sort that will fit into the nose of a jetfighter or a missile), this gives the radar good angular resolution, at the expense of higher propagation loss (atmospheric absorption generally increases with frequency) and shorter wavelengths are easier for a target to absorb (Radar Absorbent Material) or deflect away from the source (eg angular shape of F117).Longer wavelengths (VHF or even the Duga or JORN over-the-horizon HF radar systems) require much larger antennae to form a tight beam (not really practical to put a VHF radar in a SAM!), but have less propagation loss, and tend to "see through" the radar absorbent coatings and special shapes of stealth aircraft (long wavelengths are hard to absorb with thin RAM layers and fancy shapes don't deflect returns away from their source when the features of those shapes are shorter than the wavelength in question).I don't know if any military has done it yet (it would be secret), but I can imagine that an anti-stealth SAM system would probably use a low frequency radar to guide the rocket to the vicinity of the target (command guidance ala SA-2?) and then when the rocket was close enough to the target, it would use a plain old "all aspect passive IR" seeker for terminal guidance...Dare I say it, stealth technology is probably of more use for an aircraft bombing someone else's country rather than stopping their aircraft from bombing your country.

author: Bud
author_rank: Super Contributor
timestamp: September 25, 2016, 04:27:16 am
content: Here is some newshttp://www.extremetech.com/extreme/236167-china-claims-to-have-invented-quantum-radar-that-could-render-entire-us-stealth-fleet-obsolete

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 25, 2016, 04:36:52 am
content: Isn't stealth just a way to make a jet fighter have the same impedance as free air? There's no reflections on a matched line ... so...

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: September 25, 2016, 05:17:34 am
content: Quote from: Alex Eisenhut on September 25, 2016, 04:36:52 amNot entirely. Some aspects of stealth (like radar absorbers) do this, but otherwise the geometry assumes monostatic radar (transmitter and receiver are co-located) so it attempts to reflect energy away from its source. Hence the funny shapes.

author: Voodoo 6
author_rank: Regular Contributor
timestamp: September 25, 2016, 06:02:23 am
content: Basically what they have at the White Sands test stand is a pylon, its about 40 feet in the air. where you place your sample model on the top of, it gets zapped with every conceivable emission imaginable. The rcs is determined. Coatings and all.

author: zl2wrw
author_rank: Regular Contributor
timestamp: September 25, 2016, 06:31:33 am
content: Quote from: Voodoo 6 on September 25, 2016, 06:02:23 amThis site has some photos of an RCS test range:http://www.otherhand.org/home-page/area-51-and-other-strange-places/bluefire-main/bluefire/radar-ranges-of-the-mojave/lockheed-martin-helendale-rcs-facility/

author: Voodoo 6
author_rank: Regular Contributor
timestamp: September 25, 2016, 07:07:59 am
content: There is nothing strange about the test ranges at White Sands my friend, they are about a 1000 meters long and you can submit any model you wish to test with any parameters. We also have some nice places to eat, if you don't mind having the finest Tex-mex and a cold beer.

author: zl2wrw
author_rank: Regular Contributor
timestamp: September 25, 2016, 07:29:42 am
content: Quote from: Voodoo 6 on September 25, 2016, 07:07:59 amThat's what I get for doing a google image search for "rcs test range" (finding that otherhand.org had some good photos, and thinking, "hey, these would be interesting to someone who has never seen an RCS test range").Nothing strange to someone with any idea about radar, but quite possibly seems strange to someone who doesn't know much about radar (or physics) to whom radio seems "magic"...

author: Voodoo 6
author_rank: Regular Contributor
timestamp: September 25, 2016, 07:53:00 am
content: Hey come on in and have a beer, and talk some radar cross sections. You can Google White Sands Missile Range.

author: Srbel
author_rank: Frequent Contributor
timestamp: September 25, 2016, 08:51:52 am
content: Quote from: MrOmnos on September 24, 2016, 08:43:33 pmIt is just propaganda. Such a huge plane to have radar reflection of 0,0001m2 is a pure fantasy. It can be detected with a ground based radad, like Soviet P-18.

author: zl2wrw
author_rank: Regular Contributor
timestamp: September 26, 2016, 06:40:35 am
content: Quote from: Srbel on September 25, 2016, 08:51:52 amIf Australian Air Power site previously linked to by Voodoo6 (repeated below) regarding China's J20 is anything to go by, whilst the B2 (which is now an old aircraft) may have a very low RCS at microwave frequencies, it probably has a significantly larger RCS at VHF and HF frequencies:http://www.ausairpower.net/APA-2011-03.htmlSo yes, you probably could detect a B2 with a P18 (VHF) radar, but if your (microwave radar guided) SAM can't lock on and track the B2 (RCS is too small to produce a useful radar return, unless the B2 is close, in which case it is probably carrying a bomb with your name on it), you would have to find some other way of shooting at it...

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 26, 2016, 08:11:25 am
content: There isn't a binary answer to this. Of course any stealth vehicle can be detected. But if the detection range is cut in half it has advantages and consequences. Reaction time is cut in half. You might have to build twice as many radars to cover a perimeter, or four times as many to cover an area. Coordinating between systems at different frequencies to achieve a system solution is hard, and makes your system vulnerable to disruptions in the communications.Who has won this interchange between many elements is only clear when actual combat occurs. The answer is frequently a surprise to all of the "experts". According to Aviation Week the shootdown of the F-117 was a result of many factors. Clever use of resources by the air defenses, including using ground observers at the launch airports with telephones to warn of raid times was part of the solution as was coordination of systems at different frequencies. Overconfidence of the attacking forces which led to using the same routes over and over allowed positioning of air defenses within their detection and engagement ranges was another contributor. Whether one successful intercept of a first generation stealth aircraft indicates the end of stealth usefulness will be debated for years.One hopes that combat doesn't actually occur, and that if it does, that your side wins. The uncertainty in that answer is one of the best levers keeping combat from happening, but it obviously isn't always sufficient.

author: Voodoo 6
author_rank: Regular Contributor
timestamp: September 27, 2016, 08:43:38 am
content: Absolutely right Catalina, some folks refer to it as the fog of war, which cannot be computed.When they say B2 spirit has RCS of 0.001 m2or F-22 Raptor has a RCS of 0.001, are these numbers valid for certain band radar or does it mean it will have the same RCS for any kind if EM radiation? What does having small RCS mean for an aircraft? Does it mean it can't be detected at all? Or does it mean, you can detect it but the RCS is so small, you can't home your missiles on it? I suspect it means, it can't be detected at all, else enemy would scramble jets.Its great asking a question like this because it sparks so many different paths of discussion. The basic concept is long wavelengths have a better chance of detecting a low rcs. Now the question becomes once detected, can we hit it. Thats the magic.

author: max_torque
author_rank: Super Contributor
timestamp: September 27, 2016, 10:49:51 am
content: Sort of "On Topic" this, BTW, is a brilliant book, and includes a lot of stuff about the development of Stealth:Highly recommended!

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 27, 2016, 02:05:48 pm
content: Quote from: Voodoo 6 on September 27, 2016, 08:43:38 amYou missed the magic of the answer. Stealth vehicles can be detected at any frequency. The magic is how hard it is to do. It is easier at long wavelengths, but hypothetically still harder than for a non stealth vehicle. So more resources are required to achieve the same defensive effect. Stealth isn't a magic cloak of invisibility, it is more like very effective camoflauge.It is kind of like personal armor. It started with people wearing corsets or tunics of hardened leather. Did it make them invulnerable? No. Did it make them harder to disable or kill? Yes. Even when armor had advanced to custom fitted steel mail with chain mail undergarments those wearing the armor weren't invulnerable. And when longbows and firearms were invented armor didn't become totally ineffective. It still would deflect a glancing shot, and reduced the damage of those shots that penetrated. As it turns out the effort of building armor and training those who wore it was larger than the effort of building projectile weapons and training their users so armor dropped out of use for a while. But it is coming back as technology has brought more effective materials that are cheaper to make and which have simpler requirements for the wearers.

author: Voodoo 6
author_rank: Regular Contributor
timestamp: September 27, 2016, 07:34:37 pm
content: I don't think anyone here is disagreeing with what you are saying Catalina, Nobody said stealth is a magic cloak of invisibility.That is a great book Max. Read it awhile back, but might need to find another copy.