A measurement is a characteristic of a detected target as determined by the radar system: range, range rate, azimuth angle, and elevation angle. Radar systems are often categorized based on the number or type of measurements they provide. Two-dimensional (2D) radar systems provide range or range rate and one angle (azimuth or elevation). Three-dimensional (3D) radar systems provide range or range rate, azimuth angle, and elevation angle. Target tracking is the following of a time sequence of target measurements. The time sequence of measurements can be continuous for a target tracking radar system. Target tracking radar systems use measurement trackers to independently track in range, range rate, and angle. The time sequence of measurements can be near-continuous for a track-while-scan radar system. For a search radar system the scan period determines the time sequence of target measurements.