Single-Target Track (STT) Radar / Conical Scan:

• Principle: In this method, the radar antenna actively follows a single target. The antenna beam is continuously pointed at the target. Early STT radars used techniques like conical scan, where the beam rotated slightly around the target's anticipated direction. Any deviation of the target from the center of this rotation would generate an error signal that was used to steer the antenna to recenter on the target.
• Advantages: Provides very accurate angular measurements and good signal-to-noise ratio for the tracked target due to continuous illumination.
• Disadvantages: Can only track one target at a time. The radar cannot simultaneously search for new targets or track multiple existing ones. This limits its utility in multi-target environments. It's also susceptible to certain types of jamming.
• Application: Historically used in fire control radars for engaging a single threat.

Track-While-Scan (TWS) Radar:

• Principle: TWS radar systems are designed to simultaneously search for new targets and track multiple existing targets while continuously scanning a designated volume of space. Instead of dedicating the beam to a single target, the radar periodically illuminates the entire surveillance volume. When new detections occur, they are correlated with existing tracks. If a detection falls within the predicted gate of an existing track, it is used to update that track's state. If a detection does not correlate with an existing track, it may be used to initiate a new track.
• Advantages: Enables true multi-target tracking capability. The radar maintains situational awareness across its entire coverage area. More efficient use of radar time and resources for surveillance and tracking.
• Disadvantages: Angular accuracy per scan is typically less than dedicated STT, as the target is only illuminated periodically. Requires sophisticated data processing to associate detections with tracks and manage track files. The update rate for individual tracks is limited by the scan rate.
• Application: Widely used in air traffic control, air surveillance, naval combat systems, and ground-based air defense radars. Modern phased array radars are particularly well-suited for TWS due to their agile beam steering capabilities.

In-depth Explanation:
The core of TWS is the track filter (e.g., Kalman Filter, discussed later). This filter takes the noisy measurements from each scan and processes them to produce a smooth estimate of the target's state. It also maintains a "track gate" around the predicted position of each target. New detections falling within this gate are considered candidates for association with that track. If no detection is found within the gate for several consecutive scans, the track may be put into a "coast" mode (predicting without updates) and eventually terminated. Handling maneuvers and false alarms efficiently are critical challenges in TWS.