Radar horizon

Imagine standing at the edge of the ocean and looking out into the horizon. You can see boats and ships on the water until they disappear from your view. This is because the earth's surface is curved, and objects obstructed by the curvature of the earth become invisible.

Similarly, radar signals can travel a certain distance before they lose their power and become too weak to detect anything. The distance that the radar signal can travel before losing its power is called the radar horizon.

From space, the earth's surface looks somewhat like a ball. Because of this, the radar horizon is a function of the distance between the two objects and the height of the radar antenna. The higher the antenna, the farther the radar signal can travel before it becomes too weak to detect anything.

So, radar horizon is simply the maximum distance at which a radar can detect a target due to the curvature of the earth and the height of the radar antenna.