RADAR TRACKING SYSTEMS

Radar Tracking Systems

Objectives Describe how a radar servo tracking system keeps the antenna pointed at the target. Distinguish between single beam, dual beam and monopulse tracking system and identify which system is accurate enough for use in a fire control system. List and explain the 6 functions of the TWS system Outline how the 3 tracking gates used by the TWS system generate position information for a target from initial acquisition through a turn.

The “Problem” Locating, Tracking and Engaging faster, more maneuverable targets from platforms that roll, pitch and yaw (рыскать)! Limitation of sensor capabilities Search Radar Fire Control (FC) Radar 1)       INTRODUCTION - The “Problem”: Locate, track and engage a fast, highly maneuverable target from your rolling, pitching, yawing platform (be it a ship, aircraft, tank or submarine) and put your ordnance “on target” when directed - not something easily accomplished manually (unless you are extremely lucky!).

FC Radar Servo Tracking Systems Motor – physically rotates antenna. Electro-hydraulic motor for large systems. Electric motors for smaller systems. Servo-mechanism – controls direction of antenna rotation. Receives two inputs: Tracker – azimuth to point at. Antenna position sensor – where antenna is pointed. 1)       RADAR SERVO TRACKING SYSTEMS - objective of this system is to keep the antenna pointed at the target and to provide this tracking information to either an operator or a fire control system.   MOTOR - a motor physically rotates the antenna. An Electro-hydraulic motor usually rotates missile launchers and large gun mounts whereas small electric motors are used for fire control directors and missile steering systems

FC Radar Servo Tracking Systems Tracker – determines target azimuth and antenna position error (magnitude and direction). Single beam system. Dual beam system. Monopulse. Gyro – Provides a stable reference for system. Negates roll, pitch and yaw. Data smoothing. .   TRACKER - determines target azimuth and senses antenna position error (magnitude and direction). GYROS - provide a stable reference for the weapon system; negates roll, pitch and yaw for data smoothing

Servomechanism Order to Motor Controller Tracker Output Position Sensor Move Antenna Servo a)       SERVOMECHANISM - controls the direction of the antenna; gets two inputs: one from a Tracker telling it what azimuth to point at and one from the antenna motor position sensor that tells it where the antenna is pointing. When the servomechanism receives a “Zero” difference between the desired and actual antenna, at that point, the antenna servo motor stops ‘cuz it’s on target!

Tracking – Single Beam Target location at the point of max return. Insufficient accuracy for weapons delivery Single Beam System - as the radar beam sweeps across the target, returns are generated. The actual target location is at the point of maximum return strength. Because this is a relatively broad region of azimuth, the target location information received from a Single Beam System will not provide high enough accuracy and is therefore insufficient for weapons delivery.

Conical Scan

Tracking – Dual Beam Ideally, target centered between two beams. Improved accuracy over single beam system Sufficient accuracy for weapons delivery. i)         Dual Beam System - two overlapping “Single” beams; target return from two beams is compared to establish target azimuth; ideally want target centered between the two beams. Provides a primitive means of keeping the radar on target. Improved accuracy over single beam system thru off-axis tracking, however, signal strength is reduced, thereby reducing range. Sufficient accuracy for weapons delivery.

Tracking - Monopulse Essentially 2 Dual beam systems One Azimuth One Elevation High accuracy Used for fire control tracking. i)         Monopulse - essentially, 2 Dual Beam Systems - one determines Elevation and one determines azimuth; four beams simultaneously transmitted; all “coded” so that the receiver can ID which return came from which beam. (Like taping 4 flashlights with 4 different color beams together). Used for Fire Control tracking 1.        Advantages: Large SNR (due closer tracking to boresight) and ECM (EA) against it are more complicated. 2.        Disadvantage: More complex system by virtue of the four separate feed horns. AZ   A C Azimuth (A + B) - (C + D) + LEFT - RIGHT EL B D Elevation (A + C) - (B + D) + ABOVE - BELOW

Range Tracking/Gates Merge of Dual Beam FC tracking system with a integration computer. Provides continuous info as to target’s “predicted” position. Early gate. Late gate. 1)       RANGE TRACKING - similar to Dual Beam angle tracking; provides a continuous “window” of ranges where the target’s predicted position is contained (called “ early and late gates”) - computed by integration. a)       If return has more area in Early Gate - range estimate too long and target is CLOSER than estimate (range error positive). b)       If return has more area in Late Gate - range estimate too short and target is FARTHER than estimate (range error negative). c)       Range Tracking can be accomplished with one or more targets and served as the basis for the Track While Scan (TWS) system. Based upon abilities of FC technician, can Range Track more than one target.

Fire Control Radar Tracking Problems Fire Control tracking always “lagged” Fire Control problem. Target possibly knows it’s being tracked by a fire control radar. Hence commence evasive maneuvers EP = Electronic Protection EA = Electronic Attack [ ...and then ES = Electronic Support ]

Track – While – Scan (TWS) Solution Track – While – Scan (TWS)

Concept of TWS Incorporate a search radar and a computer. Radar continues to perform primary functions of search (scanning) and determines target position. Radar sends position data to the tracking computer. Computer performs target tracking calculations on all target data provided. System is able to accurately predict target position. Track While Scan (TWS) LEAD the Target! Maintain target tracks in a computer with periodic information from a scanning radar. 1)       TRACK WHILE SCAN (TWS) - Servo Tracking Systems respond to error signals generated from within it’s system and can generally track only 1 target. They are said to “LAG” the tracking problem and therefore you are always playing “catch-up”. To successfully engage several fast moving, highly maneuverable air contacts that exist in the Order of Battle, the Servo systems were improved upon and incorporated with a more robust computer system to handle the increased workload. The Track While Scan System was developed to allow search radar to continuously scan while a computer maintains tracks on as many as 512 different contacts in a computer database. The track location data is periodically updated with location information from a scanning radar. For the first time, a tracking system was able to “LEAD” the target by calculating its future location using historical data stored in the track file.

Fundamentals of TWS Six Basic Functions: Target detection Track initiation and track file generation Generation of tracking “Gates” Target track correlation Track gate prediction Display Computers make Track-while-scan possible. Scanning radar information is converted into binary (computer) information. All of the fundamental action of a TWS system occur in the computer. The computer: 1. Takes the scanning radar output, does analysis of the information and determines if the returns are from a target (target detection) or just random noise. 2. Determines if the target is an target previously detected or a new target. The computer does this by comparing the information received from the previous scans. 3. If it is a new target, the computer will start a file on that target. In the file it puts the information on the target (position) and will update the information with each subsequent scan. - The computer can also add information on the target from other sensors and sources (including from other radars. 4. Generates tracking gates (small volumes) around the target. With more information the gates get smaller. 5. Track gate prediction, smoothing and positioning. Same feedback and smoothing process used in previous discussions of conical and monopulse. 6. Future target position. Uses information to predict mathematically where the target will be. Eliminates the feedback problem of always lagging the target. Designed to LEAD THE TARGET.

Target Detection Automatic Detection and Tracking (ADT). Digitizes (0’s and 1’s) scan area of search radar. Each position in search area given specific digital “address”. Once radar return received by ADT, FC solution generated for specific “address”. a)       TARGET DETECTION   i)         ADT - Automatic Detection & Tracking: (1)     Converts echo return patterns into matrix of “1” and “0” (2)     Uses sampling and encoding to convert analog  digital (3)     Once target detected and tracked, a fire control solution generated

Track Initiation and Track File Generation Track file generated to store position (address) and gate data for each track. Generation begins with initial storage of position (address) data. Lat / Long. Course / Speed. Bearing / Range /Altitude. Estimated Position (EP) data. Correlating data (from own ship). Calculated target velocities and accelerations are also stored in each track file. All data is converted from polar to rectangular coordinates by the computer. The data is used to perform various calculations necessary to maintain the track. As the data is needed for computation or new data are to be stored, the portion of the memory allocated for the data will be accessed by the system software. This method is much too slow is much too slow to be used in a system where speed of operation is on of the primary goals.        TRACK INITIATION & TRACK FILE GENERATION   i)         Computer stores position, velocity, acceleration data in track file ii)       Also stores other data such as ESM, engagement status, etc.

Gate Generation Acquisition Gate (Largest) Tracking Gate (Smallest) Turning Gate Predicted Position Tracking Gate Turning Measured * Gates are 3-dimensional pieces of space that the target occupies. * Size of Gates are determined by the computer based on the information. * Three types of Gates. 1. Acquisition gate 2. Tracking gate (smaller) 3. Turning gate (overlaps tracking gate, and varies in size depending on the speed and maneuveraability of the target.) a)       GENERATION OF TRACKING GATES - computer organizes cells into gates (volume in space) which are monitored with each scan   i)         ACQUISITION GATE: Largest, Used for Initial Position Designed to allow for max target motion ii)       TRACKING GATE: Smallest, Used for Predicted target position If target not found in this gate, generate turn gate iii)      TURN GATE: Medium size, Used to re-acquire target Larger than tracking gate Size determined by max acceleration and turn characteristics of valid track Once reacquired, gate closes to a tracking gate

TWS Gates Acquisition Gate 10 degrees 10 degrees 2000 yards

TWS Gates Tracking Gate 1.5 degrees 1.5 degrees 120 yards

TWS Gates Turn Detection Gate Tracking Gate *Dimensions of this gate are determined by computer based on speed of target.

TWS Processing Original Course Turn Gate Reacquire Target Tracking Gates Resume Tracking 1. Use the graphic to explain how gates work and the use of the tree types of gates. a. Acquisition Gate: Based only only on instantaneous position of target. b. If next scan shows the target is still in acquisition gate: - now have information to predict where the target will be next scan - so can reduce the gate size to smaller tracking gates. - Tracking gates can get smaller as get more (and better) track history. c. If target is not in a tracking gate as predicted, he must have changed course or slowed or both. - Make a larger turning gate to try to pick up the target again. - Once found subsequent tracking gates can be reduced in size. 2. Same process can be used for multiple targets. 3. When ready to fire can had over target information (position, course, speed and range to the fire control system who locks on and fires then is ready for the next target. 4. Each contact is consider a new target unless determined to be consistent with a target held on the previous scan. (in turning gate). 5. If more than one target is in a gate or if two gates overlap the the computer has protocol to sort out the contacts. If they can’t be sorted out then they are considered new targets and files are created and they are tracked. Acquisition Gate

Track Correlation System Resolution Rules. Software decisions based upon threat environment and ROE. Ambiguities resolved for: Multiple gates on same target. Multiple targets in same gate. Crossing targets. a)       TRACK CORRELATION   i)         What If? Multiple targets in same gate (1)     Multiple gates on same target (2)     Crossing targets ii)       How do we resolve ambiguities? i)         SYSTEM RESOLUTION RULES (1)     Software decision rules designed for each system a)       TRACK GATE PREDICTION, SMOOTHING, POSITION i)         TWS - moves track gate to predicted position to keep ahead of problem. (Remember: servo system - feedback via elect, mechanical means - lagged problem) ii)       Tracking gate “replaces” tracking antenna iii)      Smoothing accomplished by comparing predicted parameters with observed parameters. Reposition mathematically; uses equations for position, velocity and acceleration feedback / Tracking Algorithm. DISPLAY - provides visual format for information to be displayed to the operator - usually large screen display or PPI. Computer has algorithms to sort out conflicts (e.g., contacts swapping identification during merge) Operator must check computer results

TWS Radar System Advantages Automated tracking Track prediction Tracks multiple targets simultaneously Tracking info used to compute FC solution Tracks with only a search radar and a computer Stress the following: a. Search radar searches and identifies contacts (uses previous sweep’s information to determine if each return is that of a contact that is being tracked or is a new contact). b. Only when going to use a weapons system is a fire control radar and launcher system assigned. The target’s position and track information is then shared from the tracking computer. c. This allows continuous track on targets but receives the fine tuning of the target of interest’s parameters to the Automatic tracking system of the angle-tracking servo, feedback enhanced fire control radar.

Real World Applications AN/SYS-2 IADT (Integrated Automated Detection and Tracking) Carriers CG DDG FFG AN/ SYS-2 IADT - now used aboard missile ships. The system is used to develop a single track file based on the outputs of several files.

Tracking Recap Servo tracking systems can only handle a few, maybe just one, track(s) Likely lag the problem (fire solution slow/inaccurate) Wait for an update (radar hit) to re-position antenna and target plot Track While Scan systems can easily handle multiple targets Keep targets within predicted volume in space System is projecting ahead to where the target should be next