If the regular radars get your position close enough to launch, and the missile has a radar able to fine-tune your location once it gets close, then you’re in trouble.
There’s also laser-radar
https://en.wikipedia.org/wiki/Lidar
Who says it’s a missile what if it’s several dozen independently targeted drones equipped with AI all capable of a 100-300 mile range, the B-21 could fly in international airspace undetected and release the drones to take out all the coastal air defenses systems. Just saying