[Cicero]

My experience is mainly with marine radar, but even a cheapie radar set should be able to pick these things up. A small boat radar easily picks up lobster pots and buoys. I doubt whether these drones are sophisticated enough to escape observation.

[RightWhale]

Apparently airports don't use radar anymore. They rely on repeaters carried in aircraft that send the plane's position when queried. The position is derived from GPS, and if the repeater is inactive the plane disappears from the screen. Please correct if this interpretation is incorrect.