Full stealth jets like the F-22A Raptor create drastic reductions in radar detection range.
The Su-35S will have IRST (infra-red search and track) system to enable detection of stealth fighters like the F-22A. The F-22A will be able to spot the more detectable Su-35s at larger distances.
The SU-30 family has never been especially stealthy, and their overall airframe design limits what one can accomplish in this area. Nevertheless, Sukhoi cites an unspecified amount of “reduced reflectance” for the SU-35 in the X-band, which is a popular choice for modern radars, and in the angle range of plus or minus 60 degrees. Further improvements were made during testing by adding radar-absorbent materials, and removing or modifying protruding sensors that create radar reflection points.
The SU-35S will also depend on its sensors. It couples an electronically-scanned array radar with a 2-step electro-hydraulic drive unit, which creates a maximum radar beam deflection angle of 120 degrees. The NIIP Tikhomirov Irbis-E passive phased-array can reportedly detect and tracks up to 30 air targets, simultaneously engaging up to 8. It can also reportedly detect, choose and track up to 4 ground targets, and engage 2. Detection ranges of over 400 km/ 240 miles have been reported for airborne targets, which are the easiest, but resolutions are unspecified.
Russia and China will be able to cover airspace with stealth plane detecting radar from larger UAVs and ground stations. Having more detection systems and integrated communication allow for fourth generation fighters to remain effective against fifth generation fighters.
The Su-35S will fill a gap until the Russian T50 is developed in large quantities.
Long Eagle Hale Drone
The Long Eagle HALE drone is designed by the UAV Design and Research Institute of Beihang University. The program is said to have commenced in 2000, with a maiden flight conducted around 2004. However, the existence of the program was not officially confirmed by Chinese authorities until 2008. It is believed that the program completed around 2011 but very little information about the UAV have been revealed to the public due to alleged sensitivity surrounding its strategic capabilties.
China's largest ever UAV, the secretive Divine Eagle. Compared to other Chinese aviation projects like the J-20 stealth fighter and Y-20 heavy transport aircraft, the lack of publicly available photos of the Divine Eagle suggests that like the American RQ-180, this giant drone is a strategic and sensitive asset.
Stealth planes are never completely invisible, as they will always generate a radar signature in the end according to Douglas Barrie, senior fellow for military aerospace at the International Institute for Strategic Studies in London. If you are seen five miles from your target, compared to be being spotted 100 miles away, then it will have done its job.
Anti-stealth countermeasures are now "proliferating". Whereas most radars operate between 2GHz and 40GHz, a low-band equivalent such as VHF radar operates between 1MHz and 2MHz and is able to pick out most stealth planes that are known to be flying today.
The Russians persevered with low-band radar due to their technological conservativism.
VHF can pick up "noise" such as clouds and rain, which was a reason why the West abandoned it – it does have basic physics on its side: its wavelength is the same magnitude as the prominent features on many stealth planes, so that its signal bounces back.
Russia and China (UK, USA, Australia, Israel, South Korea and basically any country with a modern air force) have VHF-Aesa (Actively scanned electronic array) radars.
Aesa (Actively scanned electronic array) radars like those supposedly on China's Divine Eagle drone are made up of a large number of solid state, chip-like modules that each emit an individual radio wave; these meet in front of the antenna to form a beam that can be easily aimed at a very specific target – and, combined with VHF, are an effective stealth-hunting tool.