How effective is Russia's Nebo-M counter-stealth radar?

Nebo-M radar and its efficacy against stealth fighters like the F-35

Nebo-M multi-functional radar arrays. (Wikimedia Commons)

Modern stealth fighters are designed to delay or prevent detection from higher frequency radar arrays broadcasting in parts of the S, C, X, and Ku bands, because these systems are capable of providing a “weapons-grade lock,” in other words, radar arrays that can guide a missile to a target. Lower frequency radar arrays leveraging the L or S bands are not capable of guiding weapons with this sort of accuracy — but are capable of spotting stealth fighters.

As a result, many countries have developed early-warning radar systems that leverage low-frequency bands to notify them of the approach of stealth fighters. Yet most countries lack the ability to target these aircraft even when they know they’re flying directly overhead. You can read more about this in our full-length feature on the topic here.

Radar frequency band - Glossary of Meteorology

Radar frequency bands with their corresponding frequency and wavelength ranges.

Russia’s Nebo-M system uses two low-frequency radar arrays, the Nebo SVU in the VHF-band and the Protivnik G in the L-band, to detect the presence of stealth fighters as they approach. These systems do not provide the image fidelity required for targeting a stealth fighter, but by networking them with Russia’s Gamma S1 array broadcasting in the S and X-bands, the Nebo-M system offers an effective means of tracking and eventually even targeting stealth fighters.

It’s important to note that while modern stealth fighters like the F-35, F-22 Raptor, J-20, and Su-57 are all designed to minimize detection against these high-frequency bands, no modern fighter can entirely defeat detection against them. America’s F-35 is said to boast a radar cross-section (RCS) of approximately 0.0015 square meters, or around the size of a golf ball, while the stealthier F-22’s RCS of about 0.0001-0.0002 square meters is more like a marble. These both represent a significant improvement over the world’s first operational stealth aircraft, the F-117 Nighthawk, which had a claimed radar cross-section of approximately .003 square meters.

In practical application, stealth isn’t about preventing detection altogether, but rather delaying it for long enough for the fighter aircraft to either strike first or escape a potential threat. The smaller your radar return, the closer your aircraft needs to be to the array in order to be effectively targeted.

According to a peer-reviewed assessment by electronics engineer and Hellenic Air Force Colonel Konstantinos Zikidis, published by the Journal of Computations & Modelling in 2014, Russia claims the low-frequency arrays leveraged by the Nebo-M can detect the F-117 Nighthawk at a range of 350 kilometers (217 miles) in an environment free from electronic warfare (EW), and potentially as far as 72 kilometers (45 miles) under heavy jamming. This detection range is the basis for many S-400 counter-stealth claims, but it fails to acknowledge the difference between detecting a stealth fighter and targeting one.

The figures above represent the detection range for the S-400 system’s low-frequency radars versus the F-117, which offers an RCS that’s approximately 30 times larger than the F-22 and at least twice the size of the F-35. As a result, both detection and targeting ranges for these more modern fighters will be reduced dramatically.

Based on assessments, the S-400 can target aircraft like the F-35, but likely not until the jet flies within 20 miles of the system.