Conical Scanning - Concept

Concept

A typical radar antenna commonly has a beam width of a few degrees. While this is adequate for locating the target in an early warning role, it is not nearly accurate enough for gun laying, which demands accuracies on the order of 0.1 degrees. It is possible to improve the beam width through the use of larger antennas, but this is often impractical.

In order to monitor the direction of a designated target, it is only necessary to keep the antenna pointed directly at the target. Knowledge of the pointing direction of the antenna then gives knowledge of the target direction. In order to have the radar system follow a moving target automatically, it is necessary to have a control system that keeps the antenna beam pointing at the target as it moves. The radar receiver will get maximum returned signal strength when the target is in the beam center. If the beam is pointed directly at the target, when the target moves it will move out of the beam center and the received signal strength will drop. Circuitry designed to monitor any decrease in received signal strength can be used to control a servo motor that steers the antenna to follow the target motion. There are three difficulties with this method:

1. The radar will have no information as to which direction the target has moved, and therefore no indication as to which direction to move the antenna to follow it.
2. As the target moves away from the beam centre, the received power changes only very slowly at first. Thus the system is rather insensitive to antenna pointing errors.
3. Variations in target echo power caused by scintillation are interpreted as target motion.