AFAIK, stealth planes use all flat surfaces and no curves because a curved surface is more likely to reflect a signal from an active radar beam back in the direction of the detector instead of somewhere else.
If you shine a flashlight beam on a reflective sphere, you will always see a tiny spot of reflected light somewhere on the surface. If you shine a light beam on a perfectly flat surface, and it is not angled correctly, you will not see the reflection.
So stealth surfaces are designed to be as black (to radar frequencies) as possible, and as flat as possible. And if possible, you should make as many of your flat surfaces parallel to one another as you can manage, because each one sends a reflection of a radar beam to a new spot, and you don't want the spots to be widely dispersed.
In order to classify a radar reflection as natural or artificial, you have to detect it first.