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Stealth is dead.

Discussion in 'Greater Asia & Middle East' started by Picdelamirand-oil, Jun 11, 2015.

  1. Picdelamirand-oil

    Picdelamirand-oil Lt. Colonel MILITARY STRATEGIST

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    The Israel Radar is not VHF but UHF. But yes it's a low frequency radar compare to Band X. Low frequency radar can detect small target even if the target is smaller than the wavelength of the radar. The problem is the accuracy of these radar but the accuracy improve with AESA and data processing.
     
  2. vstol jockey

    vstol jockey Colonel MILITARY STRATEGIST

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    Bro, I have serious doubts on what you have stated. no radar in the world can pick up a target which has dimensions below its operating wavelength. search radars are horizontally polarized while tracking radars are vertically polarized and weather radars are circular polarized. No V/Uhf radar can be vertically polarized due to very large amount of ground clutter and also reflected signals will fail to register on the receiver.
     
  3. Picdelamirand-oil

    Picdelamirand-oil Lt. Colonel MILITARY STRATEGIST

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    I'm in Croatia with Picard to prepare the next world war, :rofl: I've no time to give a strong argument for the moment, i will return in France begining of July.
     
  4. vstol jockey

    vstol jockey Colonel MILITARY STRATEGIST

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  5. Picdelamirand-oil

    Picdelamirand-oil Lt. Colonel MILITARY STRATEGIST

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  6. Picdelamirand-oil

    Picdelamirand-oil Lt. Colonel MILITARY STRATEGIST

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    Rayleigh- versus Mie- Scattering

    The following picture shows the different regions applicable for computing the radar cross section of a sphere. The optical region („far field” counterpart) rules apply when (2π·r / λ) >10. In this region, the radar cross section of a sphere is independent of frequency. Here, the radar cross section of a sphere, σ = π·r2.

    [​IMG]
    The radar cross section equation breaks down primarily due to creeping waves in the area where 2π · r. The largest positive perturbation of the radar cross section (point A) would be 4 times higher than the radar cross section computed using the optical region formula. Just slightly a minimum occurs (point B) and the actual radar cross section would be 0.26 times the value calculated by using the optical region formula. This area is known as the „Mie” or „resonance region”.
    If we used a one meter diameter sphere, the perturbations would occur at 95 MHz, so any frequency above 950 MHz would give predicted results.
    The size of the spherical reflection area is smaller than the wavelength in the area of the „Rayleigh-Scattering”. The radar cross section is calculated the formula σ = π·r2 · 7,11 · ( 2π·r / λ )4 here. The „Rayleigh-Scattering” is a typical application case for weather radar.
    Approximately this is till lower L- Band still take the Mie scattering into account at air defense and air traffic control radar sets. There are predominantly optical conditions at frequencies above 1 GHz.
    E.g. the ancient Russian VHF-Radars operate at frequencies about 145 to 175 MHz, ie they use the wavelength of about 1.7 to 2.1 meters. This is exactly the position on the second maximum in the diagram (located over the letter B) for the geometric dimensions of a fighter aircraft.

    Radar Basics - Rayleigh- versus Mie- Scattering and Optical Region
     
  7. Picdelamirand-oil

    Picdelamirand-oil Lt. Colonel MILITARY STRATEGIST

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    In the picture the abscisse is R/Wavelength so when < 1 the target is smaller than the wavelenth and the picture shows that the detection is possible.

    So in the Rayleigh region, and in the Mie region there is detection but more complex than in the optical region. Also it's not the whole size which has to be taken into acount but the size of main structural elements its why the Russian VHF radar, with a wavelenth of around 2 meter are in the region of r/ wavelenth= 0.5 => r ~ 1 meter.
     
  8. randomradio

    randomradio Colonel REGISTERED

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    Even UHF radars are used in entomology, study of insects.

    UHF band can be used to comfortably tracks small insects when they want to study their flight patterns.
     
  9. lookieloo

    lookieloo 2nd Lieutant FULL MEMBER

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    Tee hee... Mr SNAFU also predicted that we'd all be dead of ebola by now some months ago, among other fun posts of his.
     
  10. vstol jockey

    vstol jockey Colonel MILITARY STRATEGIST

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    I am well aware of these aspects. nearly all V/UHF radars have horizontal polarisation, so the nose size and width at intakes makes a big contribution to RCS in these frequencies. If we keep them small, the RCS will reduce in these frequencies. The main reason for RCS in these freq range are creeping and travelling waves.
     
  11. BON PLAN

    BON PLAN Major SENIOR MEMBER

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    Stealth Basics

    Stealth is the science of reducing an object’s detectability to radar. The goal is to minimize the electromagnetic energy reflected back to a radar so it cannot distinguish the return from the signals created by environmental clutter and noise of its internal electronics.

    The metric of detectability is called radar cross-section (RCS), which normalizes the reflectivity of targets by comparing them to metal spheres. Human beings have an RCS of about 1 m2— they return as much radar energy as a sphere with a geometric cross-section of 1 m2. Since RCSs vary by orders of magnitude, it also is common to use the logarithmic unit “decibel square meters” (dBsm), in which 100 m2 converts to 20 dBsm and 0.1 m2 to -10 dBsm.

    Large “fourth-generation” fighters such as the F-15, Su-27 and Tornado have radar cross-sections (RCS) of 10-15 m2. The F-16 and “Gen-4.5” fighters—Typhoon, Rafale, Su-35 and Super Hornet—are believed to be in the 1-3-m2 range. The F-35 and F-22 RCSs are said to equal a golf ball and marble, respectively. Based on Sukhoi’s claims that its Su-35 can detect 3-m2 targets at 400 km in a narrow-angle, maximum-power search, Aviation Week estimated how far away it can detect these fighters. Note the detection range in a standard search is half as much. Credit: Colin Throm/AW&ST


    RCS varies with the angle and frequency of the radar signal. The sector of greatest interest is ±45 deg. in azimuth and ±15 deg. in elevation, and the frequency band of greatest concern is X-band (8-12 GHz), where most fire-control radars operate. “All-aspect stealth”—minimizing detectability from any angle—and “broadband stealth”—reducing observability over a broader frequency range—can be achieved with greater cost or engineering tradeoffs.

    Stealth technology reduces RCS by shaping an aircraft to “scatter” radar waves away from the emitter and using radar-absorbent material (RAM) to reduce reflections by turning the energy into heat. Traditionally, shaping accounts for 90% of stealth’s RCS reduction and materials 10%.

    Shaping starts with a focus on “specular” scattering, in which waves bounce off a structure like billiard balls. Flat surfaces reflect most energy at an angle equal to the incident wave and are therefore preferred and oriented to minimize returns to the radar.

    Engine intakes, cockpits, 90-deg. corners and other “multiple-bounce structures” reflect the most incoming energy back to their sources. Right angles are avoided entirely. Cockpit canopies are “metallized” with a few nanometers of gold or indium tin oxide to make them reflect radar energy. Engine fan faces can be shielded from radar illumination by external screens (F-117 and RQ-170), internal blockers (F/A-18E/F) or serpentine-shaped inlets (B-2, F-22 and F-35), all of which incorporate RAM.

    Weapons and other stores are carried internally. Missiles, bombs and fuel tanks increase RCS with their pylons, round bodies, cruciform tailfins and sensor apertures. They also create multiple-bounce geometries with the airframes, which can increase RCS.






    [​IMG]
    This front view of the F-117 shows the screens covering the engine intakes. The screen blocks most radar waves and traps the rest inside. Note also the hexagonal auxiliary intakes with edges aligned with the main intakes and side of the fuselage and the sawtooth pattern surrounding the canopy. Credit: U.S. Air Force



    Edges diffract radar energy in a narrow, fan-like pattern but still at an angle equal to the incoming wave, and wing and tail tips diffract waves in all directions. Both are kept narrow to minimize RCS, and edges are angled away from the direction of the threat.

    Fuselage facets, control surfaces, leading and trailing edges, and gaps are oriented to concentrate reflections into a minimum number of angles. This “planform alignment” reduces detectability at every other angle. The surface is then covered with RAM, with special treatments for edges and tips.



    When waves strike surfaces at grazing angles, they induce currents that travel until they hit a discontinuity, where they radiate waves and bounce back to radiate again. The longer they travel, the weaker they become, particularly if the surface contains RAM, but any discontinuity—an edge, gap or step in the surface, or a material change—reflects them. Gaps around access panels must be covered with conductive tapes or caulks to bridge any electromagnetic discontinuities. Access panels and doors that open in flight, such as those for landing gear and weapon bays, have edges angled to reflect traveling waves away from the threat sector, often creating a “sawtooth” appearance.
     
  12. BON PLAN

    BON PLAN Major SENIOR MEMBER

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    Estimating RCS

    There are formulas to calculate the RCS of simple shapes and computer programs to estimate those of more complex structures, but due to the difficulty in accounting for nonspecular mechanisms, interaction among structures and RAM, it is better to rely on RCSs determined by testing. Those numbers, sometimes cloaked in terminology of objects, have been discussed publicly.


    [​IMG]
    Almaz-Antey says the S-400’s 92N6E “Gravestone” fire-control radar can detect a 4-m2 radar-cross-section target at 250 km. Based on this figure, Aviation Week estimated its detection range against modern fighter aircraft. Credit: Colin Throm/AW&ST




    Conventional aircraft of similar geometries and size tend to have similar RCSs. TheBoeing F-15 has a frontal RCS of around 10 m2. The Sukhoi Su-27 RCS is also in the 10-15-m2 range and the Panavia Tornado is likely in this neighborhood as well. The figure is larger if external stores are carried. The initial Boeing F/A-18’s RCS is believed to be in the 10-m2 realm, but F/A-18C/Ds began incorporating RAM in 1989. The smaller Lockheed Martin F-16’s RCS is believed to be around 1-3 m2; the later C model is slightly stealthier than the F-16A, and signatures have also been reduced under Have Glass programs, which include application of RAM.

    Later “Generation 4.5” fighters all employ RCS reduction to some extent. The Eurofighter Typhoon program sought to reduce RCS by a factor of four compared to Tornado. The Sukhoi Su-35 claims reduction of 5-6 times over the Su-27. This likely puts the Su-35, along with Dassault Rafale, in the 1-3-m2 range. The F/A-18E/F, which Boeing says employs the most extensive RCS-reduction measures of any nonstealth fighter, is reported at 0.66-1.26 m2.

    While low observability is a spectrum and not a binary quality, “stealthy aircraft” usually implies an RCS of less than 1 m2. Russia’s new T-50 PAK FA is believed to be in the 0.1-1-m2 range. Cruise missiles come in at 0.1-0.2 m2. The F-117 was said to have an RCS equal to a small bird (0.01-001 m2). The F-35 RCS is compared to a “golf ball” and the F-22’s to “a marble”; these objects have RCS of 0.0013 m2 and 0.0002 m2, respectively.

    Detectability vs. Radar

    How does stealth affect survivability? Since radar waves expand spherically going to and returning from targets, the range at which an aircraft can be detected is proportional to the fourthroot of its RCS. Every tenfold reduction decreases detection range by 44%.

    The most advanced Russian fire-control radars yet deployed are the Irbis-E on the Su-35 and the ground-based 92N6E Gravestone, part of the formidable S-400 surface-to-air missile (SAM) system. The manufacturers of the Su-35 and S-400 claim good performance against “stealthy” targets, but their own numbers do not substantiate this.

    Sukhoi states the Su-35 can detect a 3-m2 target at 400 km (250 mi.). That is a good range against an F-16 or Typhoon, but it means this newest Flanker cannot detect an F-35 until it is within 36 mi., and inside 22 mi. for an F-22. And the U.S. fighters can launch their medium-range AIM-120 AMRAAMs from more than 60 mi. away. Also, that detection range is for a maximum-power, narrow-angle search. In conventional search mode, the detection range is half as much.

    Almaz-Antey’s S-400 is feared for many reasons, including its longest-range (380-km) missile, but it cannot fire until its Gravestone radar has a target. According to the manufacturer, Gravestone detects a 4-m2 target at 250 km (155 mi.). Again, good against “reduced RCS” fighters, but the F-35 would not be seen until 21 mi. away and the F-22 13 mi. away. The U.S.’s internally carried Small Diameter Bombs can be dropped from more than 40 mi. away.

    Much of the debate over the continued value of stealth has been generated by developments in lower-frequency radars (to be addressed in the next installment of this series), able to detect aircraft optimized for X-band stealth at longer range. But these are search radars that lack the resolution to provide targeting data. The S-400’s 91N6E “Big Bird” search radar can detect 1-m2 targets at 338 km (210 mi.), almost twice the range of the Gravestone, but its batteries cannot launch until the fire-control Gravestone has a target.

    These figures are only estimates, but they are based on established formulas and public data from manufacturers and specialist engineers. The numbers convey the continuing advantage of stealth fighters, which can remain undetected until well within weapons range, even against top-end fire-control radars. These numbers suggest stealth remains a strong contributor to survivability against state-of-the-art weapon systems.
     
  13. Averageamerican

    Averageamerican Colonel ELITE MEMBER

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    Planes can detect Radar signals and avoid them before the Radar detects the plane.
     
  14. BON PLAN

    BON PLAN Major SENIOR MEMBER

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    Indeed.
     
  15. Averageamerican

    Averageamerican Colonel ELITE MEMBER

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    The Small Diameter Bomb II, or SDB II, can acquire and track moving targets from distances up to 40 miles. Will be the most use bomb by planes like the F35. Rarely will they be close enough to be detected by radar.



    Notice it can jam other radars. Nor does the plane using radar have to be plane carrying the bombs.
     
    Last edited: Aug 13, 2016

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