1. Angle tracking
The accuracy of early angle tracking radars depended on the size of the beam used, and most modern radar systems obtain better angle measurement results by using monopulse tracking technology.
Tracking radar uses the offset of the target angle in the radar beam relative to the antenna axis angle to generate an error signal, which drives the servo system to track the target.
sequential lobe method
The sequential lobe method is implemented by continuously switching the pencil beam between two predetermined symmetrical positions on either side of the antenna line-of-sight axis. When the beam is switched between two positions, the radar measures the echo signal level, and the difference between the two measured signal levels is used to calculate the angular measurement error.
In order to obtain an angular error in an orthogonal coordinate system, it is necessary to know two or more switching positions of this coordinate system. Therefore, tracking in two coordinate systems can be achieved by using an antenna group consisting of four antennas or an antenna group consisting of five antennas. In the latter case, the middle antenna is used for transmission and the other four antennas are used for reception.
cone scan
On the right, when the beam is at position B, the target echo will have the maximum amplitude, and when the antenna is at position A, the target echo will have the minimum amplitude.
Assuming t = 0 is the starting position of the beam, the variable defines the distance of the target position between the antenna tracking axes. Therefore, the errors of azimuth and pitch are respectively ,
,
and then the servo system is driven to move.
2. Amplitude monopulse
Ratio-amplitude monopulse is the same as the sequential lobe method, requiring four tilted beams to measure the angular position of the target. But the four beams of the amplitude monopulse are generated simultaneously, not sequentially. Four beams are generated by one pulse through a special antenna feed.
An amplitude monopulse requires four signals to be in the same phase but have different amplitudes.
3. Phase ratio monopulse
The phase-compared monopulse has the same amplitude but different phases, and the phase-compared monopulse radar uses an array antenna consisting of a minimum of two elements for each coordinate system. The phase error signal is calculated from the phase difference between signals generated by different antenna arrays.
4. Distance Tracking
Range tracking is measured by estimating the round-trip delay of the transmitted pulse. The process of continuously estimating the distance of a moving target is called range tracking. Since the distance of a moving target changes with time, the range tracker must be constantly adjusted in order to keep the target locked in range. This process can be implemented with a split gate system, where two range gates are applied.
The front gate starts at the desired radar echo start time and continues to half the radar echo time width, and the back gate starts at the center of the radar echo and ends at the end of the radar echo. For this, good estimates of the radar echo time width and pulse center time must be reported to the range tracker so that the front and rear gates are correctly positioned on the start and center instants of the desired echo.
5. Track while scanning (TWS)
Track-while-scan radar systems sample each target every other scan interval, use complex smoothing and predictive filters to estimate target parameters during the scan interval, and emit a series of pulses once a particular target is detected to verify the parameters of the target, and then build a trace file for this target.
Once the TWS radar detects a new target, the radar initializes a separate track file for that target detection, which ensures that sequential detections of that target can be processed together to estimate future parameters of the target. Position, velocity and acceleration form the bulk of a trace file, and generally at least one other confirmatory inspection is required before a trace file can be built.