Position Servo Response Curve

The mapping between the position error and the requested velocity, known as the position servo response curve, is non-linear and takes account of:

• Stored kinetic energy in the antenna mass
• Non-ideal, power driver characteristics
• Inductive and regenerative motor effects
• Friction

Overall, the concave downward shape of the curve can be understood as follows: The angular velocity of the antenna cannot be changed instantaneously, but is limited to a rate that may depend on the velocity itself. The time integral of such velocities produces roughly quadratically shaped positions. When approaching from a far distance at high speed, the distance covered—in the time required to reduce the velocity by half— is approximately three-quarters of the initial position error.