Verm,
Radar is a straight line of sight item. The range depends on the height above the surface of the antenna and the height above the horizon of the target.
If the target is close to the surface and the antenna is too then you have a short range detection of about 24 miles over the ocean. That is why sailing ships put lookouts as high as they could as they could see farther over the horizon.
If the target is high above the surface it isn't masked by the horizon. The distance will also be farther if the antenna is raised above surface level. Range is also a factor of the strength of the signal, it's return echo and the radar crossection of the target. There can be no hard and fast answer unless youi specify all the parameters. It's like asking how far you can see through the atmosphere and not setting the conditions. If it's foggy you ain't gonna see far!
