A strong enough search radar blip that datalinked tracking assets now know where to beam. Even stealth airplanes give larger than their frontal RCS when they move in air and angles change so blips happen. Considering the Iranian IADS network of OTHs+other long-range search assets, this is not something out of the ordinary.
It becomes easier if library data is available characteristic to airframes. Iranian IADS has adapted to this in recent times.
My words on the subject from IRIAF thread
"Considering how much investment Iran has done in its IADS over the years (from overhauling MIM-23 to putting Datalinked TVC'ed HIMADS in export exhibitions in 12-14 years), I see it happening that a target specific profile library of stealth fighters or any fighters operating in and around Iran is being made and upgraded every passing day. Even modern tracking algorithms (lets say a S-300 PMU2) lock on targets after taking certain number of cues from wide low energy search beams then target is filtered through identification protocols like IFF or flight signature etc. This is a Search-Cue-Track-Filter-Lock mechanism.
RF-DNA library means AESA-FCR like Najm or Meraj just need few blips being matched in library and tracking algorithm already can jump to locking, knowing the target characteristics prior to identifying it. Suddenly an unsuspecting enemy is getting its MAWS alarmed because its being chased by a bunch of killers like Sayyad-4 chasing at 5-6 Mach while pulling G's because of TVC. Cant be jammed because of on-board ECCM, cant be dodged because it gets automatic target upgrades if it receives jamming signals. Even low RCS or stealth assets give blips when they maneuver in sky because RCS is not a constant value, its variable depending upon beam angle to the body of the aircraft. Other techniques to hide, like terrain masking or Low altitude penetration can also be negated with this technique.
So where IRIAF is a abandoned force, IRIADF is constantly stepping up its game through real time battle experience. Passive sensors of Iranian IADS see F-22, F-35, F-18E/F, F-15SE, Rafale, EF-2000, F-16C flying just KM away from its airspace daily. More dynamic data, more the IADS learns."
en.mehrnews.com
