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Track while scan

Track-while-scan (TWS) is a radar operating mode in which a scanning antenna continuously searches for new targets while simultaneously maintaining tracks on multiple detected targets by processing periodic updates from each scan.^[1]^[2] This technique integrates automatic detection and tracking functions within a single surveillance radar system, allowing it to report target positions, velocities, and trajectories to a command and control processor without dedicating the beam exclusively to individual targets.^[1]^[3] In TWS operation, the radar's antenna, typically scanning at rates of 6 to 20 revolutions per minute, illuminates potential targets across a sector using a narrow or fan beam, capturing echo returns that include range (from pulse delay), azimuth and elevation (via monopulse techniques), and velocity (via Doppler processing) data.^[2]^[1] A digital computer then processes these returns, applying algorithms such as the α-β filter or Kalman filter to correlate detections, smooth noisy data, predict future target positions, and manage tracking gates—initially wide for acquisition (e.g., 2000 yards in range and 10° in bearing) and narrowing for sustained tracking (e.g., 120 yards and 1.5°).^[2] This enables the system to handle multiple targets, updating each once per scan cycle while avoiding the need for separate precision tracking radars.^[1]^[3] TWS offers significant advantages in multitarget environments, including the ability to engage numerous threats simultaneously—such as guiding active missiles—and providing higher accuracy than simpler plot-tracking methods, particularly in elevation and velocity estimation.^[1] It is widely applied in military air defense, maritime surveillance, air superiority fighters, and surface-to-air missile systems, as well as in civilian contexts like precision approach radars for air traffic control.^[1]^[3] As of 2025, modern TWS systems incorporate AI and machine learning to handle up to 1,000 tracks simultaneously in airborne surveillance.^[4] However, it is susceptible to electronic countermeasures and generally less precise than single-target tracker modes for individual engagements.^[3] Modern implementations often incorporate integrated automatic detection and track processors to enhance performance in complex scenarios.^[2]

Overview

Definition and Core Concept

Track while scan (TWS) is a radar processing technique that enables a single radar system to conduct wide-area surveillance scanning while simultaneously maintaining continuous tracks on multiple targets, by extracting and processing tracking data from echoes received during each scan.^[1] This approach integrates automatic detection and tracking functions within the scanning radar, allowing the system to report target positions to a digital processor for correlation and prediction without dedicating the antenna to individual targets.^[2] At its core, TWS relies on periodic updates from the radar's scanning beam to build and refine target tracks in a computer-based system, contrasting with dedicated tracking radars that mechanically or electronically lock onto a single target, thereby interrupting broader surveillance.^[5] In TWS, the scanning antenna—typically operating at rates of 15-20 revolutions per minute—passes over targets multiple times per minute, providing successive measurements of parameters such as range, azimuth, elevation, and velocity to support multi-target handling while preserving the radar's search capability.^[2] This periodic illumination ensures tracks are updated efficiently, enabling the radar to monitor dozens of targets simultaneously in applications like air traffic control or military surveillance.^[1] The basic workflow of TWS begins with the radar beam sweeping across a designated sector, where received echoes are processed to detect potential targets.^[5] Echoes from known tracks are correlated with predicted positions using gating techniques, such as range and bearing gates, to confirm and update existing tracks, while new detections that fall outside established gates initiate potential tracks for confirmation over subsequent scans.^[2] This process leverages monopulse measurements during each beam pass to refine track data, ensuring seamless integration of search and tracking without mode switches.^[1] TWS distinctly differs from techniques like track-on-jam, which focuses on countering electronic jamming by maintaining tracks under interference, or dedicated fire-control modes that employ narrow-beam, high-precision tracking for weapon guidance on a single target.^[5] Unlike these, TWS prioritizes volume search with embedded multi-target tracking, avoiding the need for separate acquisition phases or slaved antennas.^[2]

Role in Modern Radar Systems

Track while scan (TWS) is a standard capability in phased array radars, where it enables the simultaneous performance of search, track, and illumination functions without dedicating the beam to a single target. This integration is particularly vital in air traffic control (ATC) systems, which rely on TWS to monitor multiple aircraft in real-time while maintaining broad airspace surveillance, as seen in phased array implementations for conflict prediction and down-linked data processing.^[6] In surveillance radars, such as those integrated into command and control networks like the AN/SYS-2 automatic detection and tracking system, TWS supports multi-mode operations including weapon control on naval platforms by fusing data from scanning radars.^[2] At the system level, TWS provides significant advantages by allowing radars to maintain tracks on dozens to hundreds of targets—up to 1,000 in advanced airborne configurations—without interruptions from mechanical beam steering, thereby ensuring continuous situational awareness in dynamic environments.^[4] This capability eliminates the need for separate fire control radars, reducing the time from target detection to engagement from tens of minutes to mere seconds and enhancing overall operational efficiency in multi-threat scenarios.^[2] TWS serves as a foundational technique for multi-function radars, acting as a precursor to advanced digital beamforming in active electronically scanned arrays (AESAs), where electronic steering allows for instantaneous beam positioning and improved track accuracy on maneuvering targets.^[2] In AESAs, this evolution enables early track formation at detection range and supports multiple simultaneous beams for enhanced TWS performance, critical for modern air-to-air and surveillance missions.^[7] As of 2025, TWS remains a core feature in the majority of operational military radars, integral to architectures requiring real-time multi-target handling and adaptability in contested airspace.^[3]

History

Origins in Early Radar Technology

In the pre-track while scan (TWS) era, early radar systems such as the SCR-584, developed by the MIT Radiation Laboratory during World War II, primarily employed manual operator intervention or single-target automatic tracking. These systems used mechanical scanning methods, including conical or spiral scans, to focus the antenna beam on a specific target for precise measurements, but this approach interrupted volume search capabilities and limited handling of multiple threats simultaneously.^[8] The TWS concept originated in the late 1940s through post-war efforts building on MIT Radiation Laboratory expertise, particularly in projects like Whirlwind at MIT, where digital computing enabled the correlation of sequential scan data to maintain target tracks without dedicated beam steering. This innovation addressed the limitations of mechanical tracking by processing detections from periodic scans to predict and update trajectories algorithmically. A key early milestone was the successful demonstration of TWS interceptions in April 1951 using Whirlwind I and a single radar at Hanscom Air Base, guiding aircraft within 1,000 yards of targets. First proposed for surveillance radars in the early 1950s, TWS represented a paradigm shift toward automated, multi-target processing integrated with ongoing search functions.^[9]^[10] Practical implementation of TWS began in the 1950s within U.S. Navy fire control systems, adapting principles from air defense research to shipboard environments for enhanced threat response. These developments were driven by escalating Cold War aerial threats, including Soviet bomber incursions, necessitating radars that could seamlessly transition from broad-area surveillance to persistent multi-target tracking without compromising detection of new intrusions.^[11]^[12]

Evolution and Key Milestones

In the 1960s and 1970s, track while scan (TWS) technology advanced through integration with monopulse techniques for precise angular measurements and digital computers for real-time data processing, enabling simultaneous multi-target tracking in complex scenarios.^[13] A key example was the PAVE PAWS system, developed in the 1970s and operational by 1980, which utilized phased-array TWS capabilities to detect and track sea-launched ballistic missiles over intercontinental ranges as part of U.S. early warning defenses. During the 1980s and 1990s, TWS shifted toward software-based implementations, incorporating Kalman filters to enhance prediction and multi-target handling in dynamic environments like air traffic control. The Airport Surveillance Radar-9 (ASR-9), introduced in the early 1980s, exemplified this by employing TWS to monitor aircraft within 60 nautical miles of airports, processing returns to maintain tracks amid clutter without dedicated beam steering.^[14] Kalman filtering became standard for robust state estimation in these systems, allowing adaptive updates to target trajectories and reducing false tracks in high-density airspace.^[15] A significant milestone occurred in the 1990s with NATO's standardization efforts for interoperable radar data formats in joint operations, facilitating shared tracks across allied systems. From the 2000s onward, TWS integrated with active electronically scanned array (AESA) radars, boosting scan agility and simultaneous operations, while recent AI advancements addressed cluttered environments. The AN/APG-77 radar, fielded on the F-22 Raptor in 2005, leveraged AESA technology for TWS modes that track up to 100 targets while scanning a 120-degree field, providing low-probability-of-intercept performance.^[16] By the 2020s, AI-assisted TWS has emerged to filter clutter and adapt to interference in urban or dense settings, with adaptive algorithms achieving over 95% tracking accuracy in multipath-heavy scenarios through real-time learning.^[17]

Operating Principles

Integration of Scanning and Tracking

In track-while-scan (TWS) radar systems, the integration of scanning and tracking is achieved by leveraging the radar's continuous surveillance mode to simultaneously detect new targets and update existing tracks without interrupting the search pattern. The radar antenna, whether mechanically rotating or electronically steered, periodically sweeps a defined volume of airspace, typically at rates of 15 to 20 revolutions per minute, to illuminate potential targets across the coverage area.^[2] During each beam pass, the system collects measurements of range, azimuth, and elevation for all detectable objects within the beam's footprint, enabling opportunistic data gathering for multiple targets in a single scan.^[5] This approach contrasts with traditional tracking radars that dwell on individual targets, as TWS maintains broad-area surveillance while extracting tracking information from transient detections.^[18] The core mechanism for tracking extraction involves associating raw detections from each scan with predicted target positions derived from prior observations, forming a seamless link between the scanning function and track maintenance. As the antenna scans, the system processes echo returns in real time, correlating new measurements—such as those from monopulse antennas that provide precise angle estimates—with established track files through scan-to-scan association algorithms.^[19] No dedicated beam dwelling occurs; instead, track updates happen opportunistically at the scan repetition interval, often every 3 to 4 seconds, depending on the antenna's rotation rate, which suffices for most airborne target dynamics.^[2] This periodic updating ensures tracks evolve smoothly without compromising the radar's ability to monitor the entire sector.^[18] TWS systems excel in multi-target environments by managing dozens to hundreds of tracks concurrently, prioritizing them based on factors like proximity, velocity, or operational relevance to allocate processing resources efficiently. For instance, the system can handle 50 to 200 or more simultaneous tracks by employing sector scanning techniques, where the beam focuses on high-interest regions for denser updates while continuing full-volume surveillance elsewhere.^[19] Data association resolves ambiguities among detections, such as by selecting the closest match to a predicted gate centered on each track, allowing robust performance against clutter and electronic countermeasures.^[2] A fundamental prerequisite for this integration is the use of pulse-Doppler processing, which employs coherent signal transmission and reception to measure Doppler shifts and distinguish moving targets from stationary clutter or noise. This technique integrates multiple pulses per beam position to estimate radial velocity, enhancing detection reliability and enabling effective track initiation and maintenance in dense environments.^[18] Without such processing, the opportunistic nature of scan-based updates would be overwhelmed by false alarms, underscoring pulse-Doppler's role in realizing TWS capabilities.^[19]

Track Prediction and Update Mechanisms

In track-while-scan (TWS) radar systems, prediction mechanisms, often referred to as coasting, extrapolate the target's state—typically position and velocity—between successive scans to maintain continuity of the track. This is achieved using dynamic models such as the constant velocity assumption, where the state vector \mathbf{x}_k = [x, \dot{x}, y, \dot{y}]^T at time k is propagated to the next scan via a linear state transition: \mathbf{x}_{k+1} = \mathbf{F} \mathbf{x}_k + \mathbf{w}_k, with \mathbf{F} as the transition matrix (e.g., \mathbf{F} = \begin{bmatrix} 1 & T & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 1 & T \\ 0 & 0 & 0 & 1 \end{bmatrix} for scan interval T) and \mathbf{w}_k representing process noise to account for minor accelerations.^[15] Such models enable the system to forecast target locations during the inter-scan period, ensuring tracks persist without dedicated beam dwelling.^[20] Upon receiving new scan data, the update process begins with data association to correlate measurements to existing tracks, primarily through gating techniques that limit computational load by rejecting unlikely associations. Gating employs ellipsoidal validation regions centered on the predicted state, defined by the measurement covariance and a statistical threshold (e.g., Mahalanobis distance \leq \gamma, where \gamma = 16 for 99% confidence in 2D), to form a validation gate that encompasses probable measurements within the innovation covariance \mathbf{S} = \mathbf{H} \mathbf{P} \mathbf{H}^T + \mathbf{R}, with \mathbf{H} as the observation matrix and \mathbf{R} as measurement noise covariance.^[21] For confirmed associations, the track state is updated using the Kalman filter gain \mathbf{K} = \mathbf{P}_{k|k-1} \mathbf{H}^T (\mathbf{H} \mathbf{P}_{k|k-1} \mathbf{H}^T + \mathbf{R})^{-1}, which optimally fuses the prediction with the measurement to minimize estimation error, yielding the posterior state \mathbf{x}_{k|k} = \mathbf{x}_{k|k-1} + \mathbf{K} (\mathbf{z}_k - \mathbf{H} \mathbf{x}_{k|k-1}) and covariance \mathbf{P}_{k|k} = (\mathbf{I} - \mathbf{K} \mathbf{H}) \mathbf{P}_{k|k-1}.^[15] Track initiation in TWS systems leverages probabilistic data association (PDA) to form new tracks from unassociated measurements, associating detections across multiple scans (typically 3–5) with a probability based on detection likelihood and clutter density, often using the joint probabilistic data association filter (JPDAF) to handle initial ambiguities by weighting potential origins.^[21] Tracks are deleted if no valid updates occur for a predefined number of scans (e.g., 3–5 consecutive misses), determined by a logic that balances false track suppression against target loss risk, with the miss probability threshold set via the track's confirmation status and environmental clutter levels. In dense or cluttered environments, where multiple measurements may fall within a single gate, ambiguities are resolved using multiple hypothesis tracking (MHT), which maintains a set of association hypotheses across scans, pruning low-probability branches via techniques like the Murty algorithm to select the k-best global hypotheses while deferring firm decisions to incorporate future data.^[22] This approach, seminal in handling non-Gaussian clutter and crossing targets, evaluates hypothesis likelihoods using mixed detection probabilities and Gaussian innovations, enabling robust tracking in scenarios with up to dozens of potential associations per scan.^[22]

Implementation

Hardware Requirements

Track while scan (TWS) radars demand robust antenna systems to enable simultaneous surveillance and multi-target tracking through periodic beam illumination of designated areas. Conventional mechanical scanning antennas, often high-gain parabolic reflectors, rotate at rates of 12 to 30 revolutions per minute to provide update intervals of 2 to 5 seconds per full 360-degree scan, ensuring sufficient data refresh for track maintenance without sacrificing coverage.^[23] For example, the AN/SPS-48G naval radar employs a mechanically driven antenna for azimuthal scanning combined with frequency scanning for elevation coverage, achieving a 4-second scan cycle.^[23] Modern implementations favor active electronically scanned arrays (AESAs), which use 1,000 to several thousand transmit/receive modules (TRMs) per array—such as approximately 2,400 elements in airborne systems—for instantaneous electronic beam steering across wide angles, supporting rapid adaptation to dynamic threats without physical motion.^[24]^[25] The transmitter and receiver subsystems must deliver high sensitivity and power to discern weak target echoes amid environmental clutter in pulse-Doppler operation. Transmitters typically generate peak powers of 1 to 10 megawatts in short pulses, as exemplified by systems achieving 1.4 MW peak output to support detection ranges exceeding 60 nautical miles against low-observable targets.^[26] Solid-state designs, like those in the AN/SPS-48G, enhance reliability over vacuum-tube predecessors, with mean time between critical failures increased by over 100%.^[23] Complementary low-noise receivers, often incorporating digital down-conversion and filtering, process multiple beams simultaneously—up to nine time-aligned channels in advanced configurations—to extract Doppler shifts and suppress interference, enabling coherent integration over scans.^[23] Real-time data handling necessitates powerful processing units to ingest and analyze voluminous scan data for track initiation and maintenance. Digital signal processors (DSPs) operating at gigaflops-scale throughput, frequently implemented via field-programmable gate arrays (FPGAs) for parallel computation, perform tasks like beamforming and clutter rejection on incoming pulse trains.^[27] These units support non-coherent and coherent detection modes, processing detections from each scan to update hundreds of tracks, as in commercial-off-the-shelf (COTS) cabinets integrating auxiliary processors for Doppler filtering.^[23] To enhance track reliability, TWS systems integrate sensor fusion with auxiliary interrogators such as Identification Friend or Foe (IFF) or secondary surveillance radars, which provide cooperative target identification to validate primary radar tracks and reduce false alarms in dense environments.^[1] This hardware linkage allows cross-verification of position data, improving overall situational awareness in operational scenarios.

Algorithms and Signal Processing

In track-while-scan (TWS) radar systems, detection begins with processing received echoes to identify potential targets amid noise and clutter, employing constant false alarm rate (CFAR) processors to maintain a constant probability of false alarm by adaptively setting detection thresholds based on local noise statistics.^[28] The cell-averaging CFAR (CA-CFAR), a foundational technique, estimates the noise power from surrounding reference cells surrounding the cell under test (CUT), computing the adaptive threshold as T = \alpha \cdot \frac{1}{N} \sum_{i=1}^N Z_i, where Z_i are the noise amplitudes in the N reference cells, and \alpha is a scaling factor chosen to achieve the desired false alarm rate P_{fa} via \alpha = N \left( P_{fa}^{-\frac{1}{N}} - 1 \right).^[28] This method assumes homogeneous clutter but can degrade in non-homogeneous environments, prompting variants like greatest-of or smallest-of CFAR for robustness against interferers.^[29] Once detections are formed, data association algorithms link these measurements to existing tracks or initiate new ones, addressing ambiguities from clutter or multiple targets. The nearest neighbor (NN) approach, a simple and computationally efficient method, assigns each measurement to the track with the minimum distance metric, such as Mahalanobis distance, assuming one-to-one associations without considering alternatives.^[30] For scenarios with clutter, probabilistic data association (PDA) extends this by computing association probabilities for all validated measurements to a track, weighting them by their likelihood and gating them within an ellipsoidal validation region, then updating the track state as a probabilistic sum: \hat{x}_{k|k} = \hat{x}_{k|k-1} + K_k \sum_{j=1}^{m} \beta_j (z_j - H \hat{x}_{k|k-1}), where \beta_j is the association probability for measurement j, K_k is the Kalman gain, and m is the number of measurements.^[31] In dense multi-target environments, multiple hypothesis tracking (MHT) manages uncertainty by maintaining a set of branching hypotheses over multiple scans, evaluating them via log-likelihood ratios and pruning low-probability branches using techniques like Murty's algorithm for hypothesis enumeration, enabling optimal or near-optimal associations in TWS radars handling up to dozens of targets.^[29] State estimation in TWS relies on Kalman filtering to predict and update target trajectories from associated measurements, with the extended Kalman filter (EKF) adapted for nonlinear radar dynamics like range-dependent measurements. The EKF linearizes the nonlinear state transition \mathbf{x}_k = f(\mathbf{x}_{k-1}, \mathbf{w}_{k-1}) and measurement \mathbf{z}_k = h(\mathbf{x}_k, \mathbf{v}_k) functions using Jacobians \mathbf{F}_{k-1} = \left. \frac{\partial f}{\partial \mathbf{x}} \right|_{\hat{\mathbf{x}}_{k-1|k-1}} and \mathbf{H}_k = \left. \frac{\partial h}{\partial \mathbf{x}} \right|_{\hat{\mathbf{x}}_{k|k-1}}, propagating the state prediction as \hat{\mathbf{x}}_{k|k-1} = f(\hat{\mathbf{x}}_{k-1|k-1}, 0) and covariance \mathbf{P}_{k|k-1} = \mathbf{F}_{k-1} \mathbf{P}_{k-1|k-1} \mathbf{F}_{k-1}^T + \mathbf{Q}_{k-1}, followed by the update \hat{\mathbf{x}}_{k|k} = \hat{\mathbf{x}}_{k|k-1} + \mathbf{K}_k (\mathbf{z}_k - h(\hat{\mathbf{x}}_{k|k-1}, 0)) with gain \mathbf{K}_k = \mathbf{P}_{k|k-1} \mathbf{H}_k^T (\mathbf{H}_k \mathbf{P}_{k|k-1} \mathbf{H}_k^T + \mathbf{R}_k)^{-1} and covariance update \mathbf{P}_{k|k} = (\mathbf{I} - \mathbf{K}_k \mathbf{H}_k) \mathbf{P}_{k|k-1}.^[29] This formulation handles nonlinear motion models, such as constant velocity or coordinated turns, common in aerial targets, though it assumes Gaussian noise and may diverge if linearization errors accumulate.^[29] Clutter rejection in TWS signal processing employs moving target indication (MTI) filters to suppress stationary or slow-moving echoes by exploiting Doppler shifts from moving targets. A basic single-cancellation MTI filter computes the difference between consecutive pulses: y(n) = s(n) - s(n-1), where s(n) is the received signal at pulse n, effectively creating a high-pass filter with a null at zero Doppler to reject ground clutter.^[32] For improved performance, multi-pulse cancellers like the two-pulse binomial filter use weights [1, -2, 1] for the transfer function H(z) = 1 - 2z^{-1} + z^{-2}, enhancing rejection of low-velocity clutter while preserving target signals with significant radial velocity, often followed by Doppler processing in staggered pulse repetition frequency (PRF) schemes to resolve ambiguities.^[32] These filters integrate with CFAR and tracking to maintain scan continuity without dedicated beam pointing.^[29]

Applications

Military and Defense Uses

Track while scan (TWS) radar technology plays a critical role in air defense systems, enabling the simultaneous detection, tracking, and engagement of multiple airborne threats such as aircraft and missiles. In systems like the U.S. Patriot surface-to-air missile platform, the AN/MPQ-53/65 phased-array radar utilizes TWS to monitor over 100 potential targets at ranges exceeding 100 km, providing fire control data for interceptors while maintaining wide-area surveillance. This capability allows for rapid response to tactical ballistic missiles and cruise missiles, supporting layered defense architectures that protect military assets and population centers. Similarly, the Russian S-400 Triumf air defense system employs TWS in its multifunctional radars, such as the 92N6E Grave Stone, to track up to 100 targets simultaneously in scan mode, with precision guidance for up to six engagements at a time, enhancing strategic deterrence against aerial incursions.^[33]^[34]^[35] In naval surveillance, TWS is integral to shipborne radars for anti-air warfare, exemplified by the AN/SPY-1 radar in the U.S. Navy's Aegis combat system. This S-band phased-array radar performs track-while-scan operations to automatically track more than 100 targets while conducting continuous horizon-to-horizon searches, integrating sensor data for missile illumination and layered defense against aircraft, drones, and sea-skimming missiles. Deployed on destroyers and cruisers, the SPY-1 enables real-time threat prioritization and coordination with vertical launch systems, contributing to fleet protection in high-threat environments. The system's ability to handle hundreds of tracks—up to 700 in some configurations—ensures robust performance in saturated attack scenarios.^[36]^[37] Ground-based early warning radars, such as the AN/FPS-115 PAVE PAWS, use phased-array technology to detect and track multiple intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) simultaneously over oceanic approaches, with enhanced sensitivity for space surveillance and satellite monitoring as secondary roles. This facilitates timely alerts to national command authorities, supporting strategic missile defense by distinguishing warheads from decoys during boost and midcourse phases.^[38]^[39] In recent military applications during the 2020s, TWS has been augmented by artificial intelligence to address emerging threats like drone swarms in conflicts, improving detection of low-observable targets. Phased-array radars with AI-enhanced signal processing enable ultrafast neural network analysis of RF signals for simultaneous identification and tracking of multiple small unmanned aerial vehicles (UAVs), as seen in counter-UAS systems tested by the U.S. Army. These advancements allow TWS to maintain situational awareness against coordinated swarm attacks, prioritizing threats for directed energy or kinetic interceptors while scanning for new incursions.^[40]^[41]

Civilian and Commercial Applications

In air traffic control systems, track while scan (TWS) enables continuous surveillance of aircraft within terminal airspace, supporting safe separation and conflict resolution. The Airport Surveillance Radar Model 11 (ASR-11), deployed by the Federal Aviation Administration, integrates TWS capabilities to detect and track multiple aircraft simultaneously using a combination of primary and secondary radar signals, providing air traffic controllers with real-time position, altitude, and velocity data essential for managing high-density traffic.^[42] This functionality facilitates automated alerts for potential collisions and maintains operational efficiency in busy airports, where radars like the ASR-11 operate in S-band frequencies to cover ranges up to 60 nautical miles.^[43] In maritime surveillance, TWS is employed in coastal radar systems to monitor vessel movements, integrating with Automatic Identification System (AIS) data for enhanced identification and tracking. For instance, Leonardo's multi-mode surveillance radars utilize TWS to maintain multiple tracks in panoramic scan mode, automatically initiating and updating target positions while fusing AIS information to distinguish cooperative vessels from potential threats, which supports search-and-rescue operations and port security.^[44] These systems operate in challenging sea conditions, providing persistent coverage over extended coastal areas to aid in collision avoidance and regulatory compliance.^[44] TWS has been adapted for weather and environmental monitoring, particularly in radar systems designed to track dynamic storm cells rather than stationary phenomena. Commercial aviation weather radars, such as the Collins Aerospace WXR-2100 MultiScan, incorporate patented TWS technology to identify and follow up to 40 storm cells simultaneously, assessing threats like turbulence and hail out to 320 nautical miles and enabling pilots to navigate around hazardous weather patterns.^[45] While less prevalent in ground-based environmental radars due to the predominance of fixed targets, this approach improves short-term forecasting of moving precipitation systems in operational meteorology.^[46] In commercial applications supporting urban air mobility, TWS-equipped airport surveillance radars are evolving to handle low-altitude drone operations for collision avoidance in densely populated areas. As of 2025, systems like enhanced versions of terminal radars integrate TWS with multi-sensor fusion to track unmanned aerial vehicles (UAVs) alongside manned aircraft, providing airspace managers with precise trajectories for safe integration of delivery drones and air taxis in urban environments.^[47] This capability draws from established surveillance principles to mitigate risks in emerging eVTOL (electric vertical takeoff and landing) corridors.^[41]

Advantages and Limitations

Key Benefits

Track while scan (TWS) radar systems excel in multi-target efficiency by simultaneously monitoring and updating tracks for numerous targets during routine scanning operations, in contrast to single-target tracking modes that dedicate the beam to one object and interrupt surveillance. This capability allows TWS to handle tens to hundreds of tracks—such as up to 24 simultaneous targets in the AWG-9 radar or at least 50 projectiles in the AN/TPQ-53 system—representing a 10-100 times increase in track capacity over single-target modes without compromising search functions or incurring dwell time losses on individual targets.^[48]^[49]^[50] A key advantage lies in cost-effectiveness, as TWS enables a single radar to perform both search and tracking duties, obviating the need for multiple dedicated systems and yielding substantial hardware and lifecycle savings. For instance, multi-mode radars incorporating TWS, such as those in active electronically scanned array (AESA) implementations, achieve approximately 40% reductions in lifecycle costs compared to legacy separate search-and-track configurations, with overall program savings exceeding $900 million across thousands of units in standardized systems.^[51]^[52] TWS enhances situational awareness through continuous track updates and predictive filtering, which facilitate superior threat assessment by correlating detections across scans and minimizing false tracks via probabilistic association techniques. This results in more reliable tracking in dynamic environments, as demonstrated by reduced track loss rates (e.g., 0% during maneuvers in spherical coordinate implementations) and improved accuracy in estimating target states.^[50]^[53] The system's scalability supports high-density scenarios, such as urban air traffic control, where it maintains low-latency updates (typically every 2-10 seconds, including 3-second intervals in airborne pulse-Doppler setups and 4-5 seconds in primary surveillance radars) to track numerous aircraft without performance degradation. This adaptability ensures robust operation amid clutter and varying target densities, prioritizing conceptual efficiency over exhaustive metrics. In 2025, advancements like the AN/SPY-6(V)4 radar demonstrated enhanced tracking of complex threats, further improving multi-target handling.^[53]^[54]^[55]

Challenges and Mitigation Strategies

One primary challenge in track-while-scan (TWS) radar systems is the limited update rate, typically occurring every 4 to 6 seconds per target due to the scanning nature of the radar, which results in sparse data and increased prediction errors, particularly for maneuvering targets.^[2] These errors arise because alpha-beta trackers, commonly used in TWS, exhibit growing deterministic and noise variances during target turns or accelerations, with track breakage probability rising as scan intervals lengthen and false alarms accumulate.^[56] To mitigate this, higher pulse repetition frequencies (PRF) can increase sampling rates, while phased-array radars enable electronic scanning for adaptive update rates, reducing radar load by up to 40% and maintaining tracking accuracy (e.g., root mean square error around 100 meters) for non-linear maneuvering models via optimized filters like the invariant extended Kalman filter.^[57] Another significant issue is susceptibility to clutter and jamming, which generate false tracks from environmental factors like weather or electronic countermeasures (ECM), degrading target discrimination in TWS modes.^[58] Advanced constant false alarm rate (CFAR) detectors, such as censored video integration variants, address this by adaptively setting thresholds in range-Doppler maps to suppress noise jamming and clutter spikes, achieving detection probabilities above 90% at jamming-to-noise ratios of 1 dB while maintaining false alarm rates near 10^{-8}.^[59] Frequency agility further counters these threats by varying carrier frequencies pulse-to-pulse (e.g., over 75 MHz bandwidths), reducing clutter echoes from terrain or precipitation and enhancing signal-to-clutter ratios in modern radars, including those incorporating AI for jamming recognition as of 2025.^[60]^[61] TWS systems also face high computational demands when managing over 100 tracks simultaneously, as association and prediction algorithms process large datasets from digital arrays like phased or MIMO radars, leading to latency in real-time operations. This load is alleviated through GPU-accelerated processing for parallel computations and machine learning techniques, such as deep neural networks for track association, which reduce complexity in 3D detection and tracking by prioritizing relevant measurements and achieving efficient multi-target handling in cluttered environments. In 2025, developments like LeoLabs' scout-class radar incorporated advanced TWS for maneuvering targets, addressing computational challenges through optimized processing.^[62]^[63] In low-observable scenarios, such as stealthy or small radar cross-section targets, TWS tracks are prone to breakage due to weak returns and environmental masking, interrupting continuity during fades or occlusions.^[64] Sensor fusion with electro-optical/infrared (EO/IR) systems counters this by integrating radar's range-velocity data with EO/IR's high-resolution imaging for validation, employing fuse-while-track algorithms that correlate non-kinematic features across unsynchronized sensors to sustain tracks in littoral or cluttered settings.^[65]^[58] This hybrid approach enhances reliability for low-signature targets, such as unmanned aerial vehicles, by reducing false alarms and extending detection beyond radar horizons.^[64]

References

[1]
Track-While-Scan - an overview | ScienceDirect Topics
Track-While-Scan (TWS) refers to a type of surveillance radar that simultaneously detects and tracks multiple targets by reporting their positions to a radar ...
[2]
Chapter 6 Track-While-Scan Concepts
The combination of automatic detection and tracking (ADT) functions within a search radar is sometimes referred to as Track-While-Scan (TWS) (figure 6-1).
[3]
TWS Radar: Advantages and Disadvantages - RF Wireless World
Introduction: TWS stands for Tracking While Scan. As the name suggests, it's a radar system designed for both searching for and tracking targets simultaneously.
[4]
Radartutorial
### Summary of Track-while-scan Radar from https://www.radartutorial.eu/02.basics/Fire-control%20radar.en.html
[5]
[PDF] 9. Manual Control Theory Applied to Air Traffic
The installation of track-while-scan (phased array) radars, and com- puter prediction of conflicts possibly based on down-link transmission of airborne ...
[6]
The Current State of Airborne Radar Surveillance in 2025 and Beyond
Feb 21, 2025 · Backed by an industry-leading number of radar integrations and decades of ISR expertise with over 600 installations in over 60 countries, ...
[7]
An introduction to digital Active Electronically Scanned Array (AESA ...
AESA – also known as E-scan – gives aircrew the ability to track multiple targets with very high accuracy and power, which is critical for modern air-to-air ...
[8]
Commemorating the SCR-584 radar, a historical pioneer
The pioneering WWII-era SCR-584 radar developed at the MIT Radiation Laboratory in the 1940s was put to use in Lincoln Laboratory's mid-1950s tests of the ...
[9]
[PDF] Project Whirlwind A Case History in Contemporary Technology
MIT Radiation Laboratory he asked for men with a radar design background ... screening, automatic track-while-scan, and the control of a large number ...
[10]
[PDF] Track Initiation Techniques in a Dense Detection Environment - DTIC
Track-while-scan systems were first proposed for surveillance radars during the 1950's. If the probability of detection per scan is high, if accurate ...
[11]
The Legacy of the United States Cold War Defense Radar Program
During the late 1940s and 1950s ... This radar was often paired with the AN/FPS-3 search radar during the early 1950s at permanent network radar sites.
[12]
[PDF] the Legacy of the United States Cold War Defense Radar Program
Jun 1, 1997 · This radar was often paired with the AN/FPS-3 search radar during the early 1950s at permanent network radar sites. AN/CPS-5. Bell Telephone ...<|control11|><|separator|>
[13]
[PDF] Radars for the Detection and Tracking of Ballistic Missiles, Satellites ...
This article is an overview of the forty-plus years in which Lincoln. Laboratory has been developing and applying radar techniques for the long-.
[14]
[PDF] Evaluation of Radar Performance Degradation Due to ... - DTIC
This thesis evaluates the performance degradation of Airport Surveillance. Radar(ASR-9) due to standoff Jamming. ASR-9 data was taken from open literature ...
[15]
[PDF] Tracking and Kalman Filtering Made Easy
1 g–h and g–h–k Filters. 3. 1.1 Why Tracking and Prediction are Needed in a Radar. 3. 1.2 g–h Filters. 14. 1.2.1 Simple Heruistic Derivation of g–h Tracking ...
[16]
[PDF] Evolution of Standard: The STANAG 4607 NATO GMTI Format
Feb 3, 2005 · Some examples of new features for future versions of the STANAG include: Track Data;. Space Borne Radar; MTI derived from Motion Imagery; and ...
[17]
AN/APG-77 Radar System - GlobalSecurity.org
Jul 7, 2011 · This feature allows a single APG-77 radar to carry out multiple functions, such as searching, tracking, and engaging targets simultaneously.<|separator|>
[18]
(PDF) AI-Driven Adaptive Radar Systems for Real-Time Target ...
Aug 6, 2025 · Radar systems play a crucial role in target tracking within urban environments, where challenges such as clutter, multipath effects, ...Missing: scan 2020s
[19]
[PDF] CHAPTER 17 - Helitavia
In addition, the computer performs the multiple-target track functions when the radar is in a track-while-scan mode and may execute radar self-test and ...
[20]
None
### Summary of Track-While-Scan Radar from MIT Lincoln Laboratory Document
[21]
Kalman filter based target tracking for track while scan data processing
To predict target parameters (future samples) between scans, track while scan radar system sample each target once per scan interval by using sophisticated ...
[22]
(PDF) Data Association Algorithms for Multiple Target Tracking
... track-while-scan. system,. the. kth. sample. will. occur. approximately. at. time. kT ... radar.) Step. 5: Validate. the. measurements. using. gating. test: Forct.
[23]
An algorithm for tracking multiple targets | IEEE Journals & Magazine
The algorithm initiates tracks, accounts for false reports, uses Kalman filters, calculates probabilities, and clusters targets for independent processing.
[24]
AN/SPS-48G > United States Navy > Display-FactFiles
Sep 20, 2021 · The radar set is comprised of 30 individual units that combine to form four major functional areas: Transmitter, Receiver/Processor, Antenna and ...
[25]
Phased Array Radar - NOAA Weather Program Office
PAR uses an integrated, flat antenna which contains an array of thousands of individual elements that scan electronically, rather than mechanically, so the ...<|separator|>
[26]
Airborne Phased Array Radar (APAR) - Earth Observing Laboratory
Each AESA is approximately 1.8 m x 1.8 m in size and is consists of ~2,400 transmitting/receiving antenna elements.Missing: while | Show results with:while
[27]
[PDF] The Radar Equation - MIT Lincoln Laboratory
Track Radar Equation. • When the location of a target is known and the ... Example - Airport Surveillance Radar. • Problem : Show that a radar with the ...Missing: While | Show results with:While<|separator|>
[28]
A fully-hardware-type maximum-parallel architecture for Kalman ...
A fully-hardware-type maximum parallel FPGA-based Kalman tracking filtering coprocessor in a track-while-scan (TWS) radar system has been designed and presented ...
[29]
[PDF] rca review - World Radio History
Adaptive Detection Mode with Threshold Control as a Function of. Spatially Sampled Clutter-Level Estimates. 414. H. M. FINN AND R.S.. JOHNSON. RCA Technical ...
[30]
Multiple-Target Tracking - Radar - Artech House
A comprehensive discussion of all the necessary information required for the design of multiple-target tracking (MTT) surveillance systems.
[31]
[PDF] An Algorithm for Tracking Multiple Targets
D. B. Reid, “A multiple hypothesis filter for tracking moltiple targets in a cluttered environment,” LMSC Rep. D-560254, Sept. 1977. Donald B. Reid (S'69-M ...
[32]
Tracking in a cluttered environment with probabilistic data association
This paper presents a new approach to the problem of tracking when the source of the measurement data is uncertain.
[33]
[PDF] CHAPTER 15 - Helitavia
The purpose of moving-target indication (MTI) radar is to reject signals from fixed or slow-moving unwanted targets, such as buildings, hills, trees, sea, and.
[34]
AN/MPQ-53/65 Radar - Missile Defense Advocacy Alliance
[iii] The radar can detect and track more than 100 potential targets and has a range of over 100 km. [iv] Being that the MPQ-53 has no moving parts, it makes ...
[35]
AN/MPQ-53 - Radartutorial.eu
The radar system has a capacity to track up to 100 targets and can provide missile guidance data for up to nine missiles. AN/MPQ-53 (PAC-3) is also known as AN/ ...
[36]
Almaz-Antey 40R6 / S-400 Triumf / SA-21 SAM System ...
The radar can track 100 targets in Track While Scan mode, and perform precision tracking of six targets concurrently for missile engagements. data exchanges ...
[37]
AN/SPY-1 Radar - Missile Defense Advocacy Alliance
The SPY-1 can maintain continuous radar surveillance while automatically tracking more than 100 targets at one time. Public numerical figures on the SPY-1 ...
[38]
[PDF] SPY-1(V) (AEGIS) - Archived 5/98 - Forecast International
May 3, 1998 · Track initiation processing is integrated with the advanced signal processor with a track-while-scan capability that uses the rapid horizon ...
[39]
AN/FPS-115 PAVE PAWS Radar - FAS
Mar 6, 2000 · The radar is used primarily to detect and track sea-launched and intercontinental ballistic missiles. The system also has a secondary mission of ...Missing: 1960s monopulse digital<|separator|>
[40]
PAVE PAWS | Military Wiki - Fandom
This ability is known as "track while scan". The large fixed antenna array through its better beam focusing, improves system sensitivity and tracking accuracy.
[41]
Drone Swarm Detection Using Artificial Intelligence Based on ...
The Army seeks AI using ultra-fast neural networks to detect drone swarms by analyzing RF signals, with simultaneous, ultra-fast identification and targeting.
[42]
A Survey on Detection, Classification, and Tracking of UAVs using ...
Mar 7, 2025 · Pulse based phased array radar, Detection range, range and velocity resolution, and track while scan capability, Detection range up to 10 10 ...
[43]
[PDF] Modeling and Simulation of a Ground Based Sense and Avoid ...
The ASR-11, which is the radar system used for our GBSAA concept, is a Moving Target Detector (MTD), constant false alarm rate (CFAR), track-while-scan (TWS), ...
[44]
Airport Surveillance Radar (ASR-11) - Federal Aviation Administration
Sep 22, 2025 · Airport Surveillance Radar (ASR-11) is an integrated primary and secondary radar system that has been deployed at terminal air traffic control sites.
[45]
[PDF] Surveillance Radars MULTI-MODE MULTI MISSION RADAR
• Track While Scan: Up to 1000 tracks, with Automatic. Track Initiation (ATI). • Track Identification: AIS and Inverse Synthetic Aperture. Radar (ISAR). • Mode ...
[46]
Maritime Surveillance - an overview | ScienceDirect Topics
The radar operates in panoramic scan mode and tracks all detected targets using track-while-scan. If the radar is fitted with an ISAR mode, it can produce ...
[47]
WXR-2100 MultiScan ThreatTrack™ Weather Radar
The WXR-2100 MultiScan ThreatTrack™ detects and analyzes adverse weather phenomena and automatically displays weather that is a threat to your aircraft.<|separator|>
[48]
The Storm Cell Identification and Tracking Algorithm - AMS Journals
This paper discusses SCIT, an algorithm that was developed to identify, characterize, track, and forecast the short-term movement of storm cells identified in ...
[49]
[PDF] Assessing Performance of Radar and Visual Sensing Techniques ...
Radar-based tracking shows a lower coverage mainly due to ground clutter removal challenges but provides comparable detection ranges and meter-level range ...
[50]
[PDF] AWG-9/APG-71(V) - Archived - Forecast International
Nov 3, 1999 · In the track-while-scan operating mode, the computer generates up to 24 target track files while the radar scans. The computer performs ...
[51]
[PDF] ATP 3-09.12: Field Artillery Target Acquisition - BITS
Jul 24, 2015 · The AN/TPQ-53 uses either enhanced track-while scan or track-while scan for its search strategy, depending on mode. This extremely efficient ...
[52]
None
### Summary of Track-While-Scan (TWS) Radar from Chapter 11
[53]
AESA's Advantages - Avionics International
Sep 1, 2008 · On a practical level, the AESA radar "will register a 40 percent savings in life cycle costs over the legacy systems," said Patrick Geraghty, ...
[54]
[PDF] Development of Acquisition Strategies for the Common Multi-Mode ...
Jan 1, 1980 · " Track While Scan (TWS) - adds capability for detecting and tracking ... potential standard system costs savings over a separate radar and ...
[55]
[PDF] On the Choice of the Coordinate System and Tracking Filter ... - DTIC
This report is part of a study into the performance of the Track-While-Scan (TWS) mode of an airborne pulse Doppler radar, and as such represents a contribution ...Missing: Barton Albersheim<|control11|><|separator|>
[56]
What is the range and accuracy of ATC radar systems?
Dec 18, 2013 · The accuracy depends on the type of antenna, whether it is primary or secondary radar, and the distance of the aircraft from the radar head.
[57]
[PDF] l Tracker for Maneuvering Targets - DTIC
The behavior of the a-,3 tracker or filter which is found in track-while-scan randars was investigated under various situations First the target's motion ...
[58]
Fully adaptive update rate for non‐linear trackers - IET Journals - Wiley
Dec 1, 2018 · Phased-array multifunction radars are designed to perform several tasks in parallel such as surveillance, also called track while scan (TWS), ...
[59]
Radar Challenges, Current Solutions, and Future Advancements for the Counter Unmanned Aerial Systems Mission
- **Coupling Radar with EO/IR**: The document discusses integrating radar with electro-optical/infrared (EO/IR) sensors to enhance detection accuracy and mitigate false positives in counter-unmanned aerial systems (C-UAS) missions. This fusion improves target discrimination by combining radar’s range and speed data with EO/IR’s visual confirmation.
[60]
https://apps.dtic.mil/sti/tr/pdf/ADA083837.pdf
[61]
[PDF] Clutter Suppression in Radars by an Application of Digital ... - DTIC
Jun 6, 2023 · FREQUENCY AGILITY. Frequency agility is a technique which enables one to achieve a measure of clutter reduction by changing the. 9*. -. - . -46 ...
[62]
[PDF] Advances in Anti-Deception Jamming Strategies for Radar Systems
Mar 1, 2025 · Interpulse agility (e.g., PRF and frequency agility) prevents CRDJ attacks from coherently replicating full pulses, whereas intrapulse ...
[63]
Vision‐Based UAV Detection and Tracking Using Deep Learning ...
Feb 18, 2025 · Track While Scan (TWS) is used to simultaneously track existing targets and scan for new ones, optimizing active tracking tasks and detecting ...
[64]
[PDF] A Survey on Radar Techniques for Detection,Tracking, and ...
Aug 30, 2022 · Passive imaging sensor EO/IR can be used to detect, track, and classify small RCS and stealthy aerial vehicles with high precision. EO/IR ...
[65]
Fusion of Radar and EO-sensors for Surveillance - TNO RESOLVER
Various architectures are considered and it will be argued that a fuse while track algorithm is the most suitable algorithm in this case. Discussed is how ...Missing: scan breakage low observable