>>22782315This gets really complicated and into classified territory for ultra-modern jets and radars, but in principle a radar works two ways. There's no way to use radar on a plane without also notifying the plane that there's a radar painting it. Think of it like a bunch of people in a closed stadium with flashlights. In order to see anybody, you need to turn on your flashlight, but as soon as somebody turns on a flashlight, you are telling everybody where you are.
This is a hugely over-simplifying, but this is how it worked for a long time. Modern jets/radars get really weird with how they use and aim their radars in ways that are very hard to detect. Passive detection of other aircraft (i.e. without using your own radar) is also a bigger and bigger deal now because it lets you move around and attack without being known.
