It doesn't have to. It's the sensor in a sensor/shooter team. The shooter will be using a VLRAAM from over 200 miles out, guided by the J-20. It only
has to get close enough to lock them up.
You don't have to get there undetected. If you can get within range long enough to lock, and let your shooter get the shot off, you're set. If you can
stay alive long enough to give guidance to the missile even better, but the key to all stealth is reducing detection time to get in weapons range.