Target tracking

B SRINIVAS ASSOCIATE PROFESSOR

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1. Introduction

• Tracking radar systems are used to measure the targets range, azimuth angle, elevation angle, and velocity

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• Predict the future values

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• Target tracking is important to military and civilian purposes as missile guidance and airport traffic control

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Target tracking

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Targets are divided to two types:

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1- Single target

2- Multiple targets

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�Single target �

1- Angle tracking

A- Sequential lobing

B- Conical scan

C- Amplitude compression monopulse

D- Phase compression monopulse

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2- Range tracking  

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• ��Relation between beamwidth and accuracy��Antennas with wide beamwidth are less accuracy than antennas with narrow beam

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���Pencil beam���In tracking processes radar used narrower beams

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��Line of Sight (LOS) axis� �The LOS is called the radar tracking axis too

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Error signal

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• Describes how much the target has deviated from the beam main axis

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• Radar trying to produce a zero error signal

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• Azimuth and elevation error

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Single target

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1. Sequential lobing

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• Sequential lobing is often referred to as lobe switching or sequential switching

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• Accuracy depends on the pencil beam width

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• It is very simple to implement

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SCR- 268�

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Concept of operation:

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• Measuring the difference between the echo signals voltage levels

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���1- When the target being on the LOS��The difference between the echo signals voltage in (A) and (B) equal zero, that’s mean zero error signal

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���2. When the target being off the LOS��Signal in position(A) will attenuate more than signal in position(B) , that’s mean a nonzero error signal

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Matlab Code

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Echo Signal A

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Echo Signal B

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Difference between A and B: �1- A>=B, theta = 0

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2- A<B, theta = 180

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• ���2. Conical scan��- It’s an extension of sequential lobbing�- The feed of antenna is rotating around the antenna axis �

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���- The envelope detector is used to extract the return signal amplitude��- AGC is used to reduce the echo signal amplitude if it is strong and raises it when it is weaker

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Elevation and azimuth error

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1- When the target being on the LOS

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2. When the target being off the LOS

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3. Amplitude compression monopulse

• This type is more accurate than sequential and conical scanning

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• Feed generated four beams simultaneously with single pulse

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• The four beams are inphase but have different amplitudes.

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AN/FPQ-6 C-band monopulse precision tracking radar

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Horn antenna generated 4 beams

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���Four beams shape��Four feeds mainly horns are used to produce the monopulse antenna pattern�

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Simplified amplitude comparison monopulse radar block diagram

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���When the target being on the LOS��radar compares the amplitudes and phases of all echo signals of target

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When the target being off the LOS

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• To move the servosystem on the target we need to calculate Error signal output

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������������Error signal output����To calcualte the error signal output first we need to calculate azimuth and elevation error��������

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• Azimuth and elevation error can be calculated by using Microwave comparator circuitry

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Microwave comparator circuitry

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Matlab code

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Two echo signals at squint angle (phi=0.4 rad)

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Sum of the two signals S1,S2

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Difference between S1,S2

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Elevation Error signal

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4- Phased compression monopulse

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• It’s the same as the last type but the amplitude here is equal for the four beams with different phases

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• Phase comparison monopulse tracking radars use a minimum of a two-element array antenna

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Single coordinate phase monopulse antenna

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Range tracking��- Target range is measured by estimating the round-trip delay�

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Split Gate System

• It consist of two gates:

1-Early gate

2- Late gate

• The early gate produces positive voltage output but the late gate produces negative voltage output.
• Subtracting & integration
• Output is: zero, negative or positive

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Split range gate �- Its predict the target movement�

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Multiple target

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Multiple Targets

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Here the system is more difficult since:

• Tracking
• Scanning
• reporting

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Track while scanning (TWS)

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• This type of radar is used for multiple targets

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• It scans for new targets while its tracking old targets

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• When TWS scan a new target it initiates a new track file

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Any Tws Radar Make

• Target detection
• Generation of tracking “Gates”
• Target track initiation and track file generation (if a new target)
• Correlation
• Track gate prediction, smoothing and positioning
• Display and future target calculations

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Target Detection

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This task is accomplished by two method :

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• Circuit in receiver
• signal-processing equipment

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Generation Gate

• Gate : small volume of space consist of many of cells

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• Function : monitoring of each scan of the target information

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• Gating has responsibility for knowing if new/exist target

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Gate Types

• Acquisition gate
• Tracking gate
• Turning gate

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Acquisition Gate

• This gate is large to facilitate target motion cross one scan period

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�Tracking Gate�

• This gate is generated when the target is within the acquisition gate on the next scan

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• It is very small gate

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• It is moving to the new expected target position

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Tracking Gate

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Turning gate

• It is generated if the observation within the

tracking gate doesn’t appear

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• It has larger size than tracking gate

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• Tracking gate included by it

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Turning gate

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Target track correlation and association

• All observations site on the boundary of tracking gate must be correlate with that track

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• Each observation is compared with all track files

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• Perhaps, observation is correlated with one track files ,several tracks or no tracks

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Tracking Ambiguity Results

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• If the observation correlates with more one track files, tracking ambiguity is appear.

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• Two reasons cause this result:

1- several targets site in the same gate

2- several gates overlap on a single target

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How To Solve Ambiguity?

• If the system designed so that an operator initiate the tracks, then solution by delete

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• But for the automatic systems , the solving by maintain software rules

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Target track initiation and track file generation

• The track file is initiated when acquisition gate is generated

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• Track file store position and gate data

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• Each track file occupies position in the digital computer's high-speed memory

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• Cont. refreshed data

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�Track gate prediction, smoothing and positioning�

• Error Repositioning Smoothing

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• The system lagged the target

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• The system leading the target

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• smoothing is completed by comparing

predicted parameters with observed parameters

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TWS System Operation

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Conclusion

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• We discussed the concepts of the different ways to determine the angle of a target and its range

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• We show the different between single and multiple targets tracking

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• We try to apply that on Matlab .

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References

1- Radar Handbook

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Author : MERRILL I. SKOLNIK

Book edition: Second Edition

Publisher: McGraw-Hill

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2- Radar Systems Analysis and Design Using MATLAB

Author : Bassem R. Mahafza

Publisher: CHAPMAN & HALL/CRC

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3-Fundamentals of Naval Weapons Systems

http://www.fas.org/man/dod-101/navy/docs/fun/part06.htm

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Questions?

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