Radar(beyond visual range for aircraft)

[Kipper]

I'm not sure about flying under radar being some arbitrary thing defined by altitude. Radar can detect anything it's pointed at, regardless of height - its just that radars tend to point slightly upwards to remove ground noise - and to see over terrain.

It balances itself, if you put radar in the open, it can detect more but it's more vulnerable. If you hide it behind stuff, it's blinded in those directions in which there are obstacles, but also shielded by them.