Entering service from 2014, the Su-35 heavyweight fighter is currently the most capable in the Russian inventory and represents the latest of a series of heavily enhanced derivatives of the top Soviet air superiority fighter the Su-27 Flanker. Initially developed for export, the cancellation of the MiG 1.42 fifth generation fighter program in 1999, and delays to the more ambitious Su-57 program, forced the Russian military to rely on ‘4++ generation’ aircraft with close to 100 Su-35s being acquired in the 2010s and more on order in the 2020s. The Su-35’s primary sensor, the Irbis-E radar, is relatively well known. The radar uses both electronic and mechanical scanning, with a passive phased antenna array mounted on a two-step hydraulic drive unit. The drive unit turns the antenna mechanically to 60° in azimuth and 120° in roll, while the the antenna scans using an electronically controlled beam in azimuth and angle of elevation. Using the electronic control and mechanical additional turn of the antenna allows the maximum deflection angle of the radar beams to reach a very wide 120°. The radar can scan not only widely, but also over great distances over four times those of the original Su-27’s N001 radar with the ability to track aircraft with a three square metre radar cross section up to 400km away. 

The Irbis-E has also been mounted on modernised variants of the Su-27, the Su-27SM2 and SM3, as well as on the new Su-30SM2 which is also derived from the Su-27. What sets the Su-35’s sensor suite apart from these aircraft however is that it deploys to additional front facing radars which compliment its main nose mounted radar to maximise situational awareness. Unlike the Irbis-E which uses both electronic and mechanical scanning, these two sensors embedded in the its wings’ leading edged are Active Electronically Scanned Array (AESA) radars. The twin N036B-1-01 L-band radars provide increased angular coverage, and are ideal for tracking stealth targets and for electronic warfare. AESA radars are not only more powerful than passively scanned array designs, but are also much more difficult to jam. The L-band operates in the 1.0 Ghz to 2.0 Ghz region of the radio spectrum with wavelengths of 15-30 cm, which is much longer than X-band radars of 8-12 Ghz frequency. These long wave radars are considered much more capable of detecting stealth aircraft, as most stealth fighters are optimised to evade X-band radar waves. Indeed, when the U.S. first deployed stealth fighters for high intensity combat during Operation Desert Storm in 1991 a key priority in the opening hours of the air campaign was to neutralise Iraqi long wave radars because of the threat they posed to stealth aircraft.  

The Su-35’s unusual use of L-band radars provides unique capabilities against stealth aircraft, which continue to form a growing proportion of NATO’s fighter units. The Su-35 also relies on the powerful new OLS-35 infrared search and track system which Russian sources claim locked onto American stealth fighters over Syria. It remains to be seen where the other fighter classes will in future adopt a similar approach to tackling stealth targets. China’s J-11D and J-15B which are also derived from the Su-27 Flanker use nose mounted AESA radars but it is uncertain whether they may deploy additional front facing radars. The Su-57 deploys cheek-mounted AESA radars although it is uncertain which bands these may operate in. The Su-35 itself has been exported to China and Egypt, although whether there will be further clients remains in question particularly as the cheaper Su-30SM2 and higher end Su-57 have recently become available for export and both threaten to infringe on its market share. L-band AESA radars will continue to set the Su-35 apart from other advanced Russian Su-27-derived aircraft in terms of situational awareness, and reflects a large part of the aircraft’s appeal to the Russian Air Force over rival platforms such as the Su-27SM3 or Su-30SM. 



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