(Images Rosoboronexport, RuMoD, NNIIRT, US DoD, Other)

 

Prior to the rout of Saddam's extensive IADS in the 1991 Desert Storm campaign, the Soviets did not take US stealth technology seriously. Desert Storm changed that entirely, and the Soviets launched an effort to develop capabilities to detect VLO aircraft. With the collapse of the USSR funding dried up, but Russian design bureaus including NNIIRT, well known for their line of P-18 Spoon Rest VHF band radars, continued developing new systems operating in the lower bands - from VHF through UHF to L-band.

Most stealth design features are intended to scatter incoming illumination in a controlled fashion, evidenced by the use of edge alignment, faceting and other geometrical shaping features, supplemented by the use of absorbent materials. All of these techniques are intended to defeat radars operating in the geometrical optics and less frequently, resonance regimes of scattering. The precondition for this to work is that the wavelength be much shorter than the cardinal dimensions of the shaping feature of interest. An edge aligned engine inlet of typical dimensions will perform best in the centimetric Ku- and X-bands, and less so with increasing radar wavelength.

The Russian approach has been to invest in the further development of low band radars, especially operating in the VHF band. With wavelengths of the order of a metre or more, only very large stealth aircraft (eg B-2A) satisfy the physics requirement for geometrical optics regime scattering. A fighter sized aircraft such as the JSF will see most of its carefully designed shaping features fall into the resonance or Raleigh scattering regions, where shaping is of little or no import, and skin depth penetration of the induced electrical surface currents defeats most absorbent coatings or laminates.


The physics of radar scattering depend to a large extent on the size of the radar wavelength vs the physical size of the target. In the Raleigh scattering regime, the wavelength is similar or greater in magnitude to the physical size of the target, and the magnitude of the reflection is essentially proportional to the physical size of the target. As the wavelength is reduced, the resonant region is entered, where the wavelength is comparable in size to key shaping features on the target, and the magnitude of the reflection fluctuates strongly with wavelength and aspect. Finally, in the optical scattering regime, target shaping can be used to precisely control the magnitude and direction of reflections. The high effectiveness of stealth designs against decimetric and centimetric band radars reflects the reality that for most aircraft sizes, these wavelengths are a tenth to a hundredth of the size of key shaping features (Author).

Low band radars are not a panacea for the defeat of VLO (Very Low Observable) aircraft. Their angular accuracy has been until recently poor, and the required antenna size results in ungainly systems which are usually slow to deploy and stow, even if designed from the outset for mobility. The size and high power emissions of these radars, in types with limited mobility, makes them much easier to detect and destroy than typical mobile systems operating in the decimetric and centimetric bands, which can relocate rapidly after a missile shot.

Despite these drawbacks, the older Russian low band radars still provide a valuable early warning capability, and enable cueing of other sensors and platforms. In an IADS context, a 55Zh6 Nebo, 1L13 Nebo SV, Nebo SVU or 5N84 Oborona would be used to cue the high power aperture X-band 30N6E Flap Lid series and 9S32M Grill Pan series engagement radars in the S-300PMU, S-400/S-400M and S-300VM systems to a small acquisition box in which the VLO aircraft can be found. This allows signficantly more RF power to be focussed into a small volume of space, increasing the probability of detection. Some newer radars such as the Nebo SVU are accurate enough to direct a missile shot, using the engagement radar primarily as a midcourse command/datalink channel to the missile.

Where fighters with high power aperture X-band radars are available, such as Irbis-E or Zhuk ASE equipped Su-30/35 Flanker E/G/H variants, a low band radar can provide GCI vectors to position the fighter near enough for acquisition of the target, if need be with other sensors such as an IR Search and Track set.



In practical terms one of the key advantages of VLO aircraft, surprise, is largely denied by the use of such systems. The VLO capability is still enormously valuable in terms of degrading or defeating most engagement radars and missile seekers, but the defender regains access to the early phases of the engagement cycle otherwise also defeated by VLO capability.

The US Air Force is expected to use the F-22A Raptor armed with the glide wing equipped GBU-39/B SDB to destroy a defender's low band systems in the opening minutes of an engagement, relying on the standoff range of the weapon and speed/altitude of the fighter to deny engagement opportunities by defending IADS elements being cued by the low band radars. Other fighters do not have these capabilities and become exposed to defending IADS elements.

The notion that Russian low band radars are artifacts of the Cold War with little combat value is foolish, as current production models are typically 'digitised' through most of the signal and data processing, and display components, and many now use solid state transmitters. At least one designs is an AESA (active phased array). Russian manufacturers have thus followed much the same trend as Western manufacturers, enhancing Cold War era systems designs with digital processing. More than often modern Digital Moving Target Indicator (DMTI) or digital pulse Doppler techniques are employed, exploiting the high performance of COTS computing technology, readily available in the open market and easy to ruggedise for a semi-mobile application of this kind.

Russian industry is very actively marketing digital upgrades to the P-18 Spoon Rest, and new production digital 55Zh6 Nebo UE / Tall Rack and Nebo SVU VHF radars, specifically as a "Counter-Stealth" capability.

While the JSF is frequently criticised for the limitations of its stealth capability in the mid and upper microwave bands, the compact size of this aircraft makes it highly susceptible to detection by low band radars, unlike larger aircraft such as the B-2A Spirit (US Air Force).
 

---

1Л13-3 Небо СВ Двухкоординатная РЛС дежурного режима
1L13-3 Nebo SV 2-Dimensional Surveillance Radar

Additional Images (1) and (2) Here (Images via NNIIRT)

---

1Л119 Небо СВУ  МОБИЛЬНАЯ Трехкоординатная РЛС дежурного режима
1L119 Nebo SVU Mobile 3-Dimensional Surveillance Radar

Nebo SVU VHF AESA Analysis [Click for more ...]

---

CETC JY-27 VHF Band Long Range Surveillance Radar

---

РАДИОЛОКАЦИОННАЯ СТАНЦИЯ 51У6/39Н6Э «КАСТА-2Е1» / «КАСТА-2Е2» /
П-15 / П-15M / П-19
51U6/39N6E Kasta 2E1/2E2 /
P-15 / P-15M / P-19 Flat Face E / Squat Eye E Surveillance Radar



Kasta 2E1 Flat Face E UHF Acquisition Radar.





Kasta 2E2 Squat Eye E





P-15 Flat Face







Stowed Configuration Images (1) and (2) Here.



P-19 Flat Face.




1L13 Nebo SV