The phrase "under the radar" has been used in historical accounts, military writing, etc. The idea is the same as not seeing things over the horizon. How does this work on FE? Seems like the radar would see everything out to the limits of its range on FE. Simple explanation on RE, no explanation on FE? Explanation of "under the radar" on FE?
Theoritically, if the earth was flat, you could have a surface search type radar of unlimited range because there is no horizon at a limited distance on a flat earth.(Big question mark on that. Where and how far is the horizon on a flat earth ? )
It would be a bit impractical, though.
The Pulse Repetition Rate (the time between when the radar transmits, bounces off an object and returns to the receiver) would be so slow and long that this would not be practical.
And the transmitter power would probably be so high it would be impractical.
The range of the typical WWII Navy surface search radar was limited by the range it could "see" to the horizon.
Which was limited by the height of the antenna.
The same as the range of the lookout in the crow's nest was limited by his height above the level of the sea.
Because of the curvature of the earth.
The WWII Navy SG-1b Surface Search Radar had a maximum range of about 12 miles with an antenna mounted on a mast 100 feet above sea level.
(Using the formula : d (distance to the horizon - in miles) = 1.2 (Constant) x h (square root of the height of the antenna - in feet) )
Of course, this was just one radar system.
There are many other types with different designs, etc. affecting the maximum range.
Bottom line :
The earth is not flat. It has no curvature.
The earth is round. It has a curvature.