This is how air defence works. At the front, you have early warning radars. These are not precise radars, but it is also more difficult to jam them. They might utilize UHF/VHF band so even stealth radars cannot evade them. You have trained operators manning them. As soon as they see something suspicious, they might scramble jets. At this point, the unknown object is a bogey. Along with the jets, an AEWACS may take off. Conversely, if planes are on CAP, they might be called in. These eyes in the air allow you to get a more precise picture.
In all of this, if a hostile enemy manages to evade your early warning system, you are potentially in deep trouble. Your jets and AEWACs will not even come into play.