A Tutorial on Radar System Engineering
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This document presents an extensive overview of radar systems, including components, operations, and functionalities. It details the design and performance of various radar components such as antennas, transceivers, and transmitters, emphasizing the differences between magnetron and solid-state transmitters. A significant focus is placed on pulse compression techniques and their implications for radar waveform design and detection performance.
![23
Antenna System
• Antenna performance:
Main Parameters:
Frequency band 9.14 - 9.47 [GHz]
VSWR
9.345 - 9.405 GHz ≤ 1.15
9.140 - 9.470 GHz ≤ 1.20
Gain ≥ 38 [dBi]
Integrated Cancellation Ratio ≥ 15 [dB]
Azimuth Pattern:
Horizontal BW @ -3 dB ≤ 0.35 [º]
Side lobe level
± 1.5º to ± 5º ≤ -28 [º]
± 5º to ± 10º ≤ -30 [º]
Exceeding ± 10º ≤ -35 [º]
Elevation Pattern:
Elevation beam form Fan
Vertical BW @ -3 dB ≤ 11 [º]
Min. coverage @ -30 dB -18 [º]
Tilt (fixed) -1.5 [º]](https://image.slidesharecdn.com/ieeeatcradarsystemengineeringv3-151016034043-lva1-app6891/85/A-Tutorial-on-Radar-System-Engineering-23-320.jpg)
![48
Radar Waveform
• The Chirp Pulse:
Time
Amplitude
Time
Frequency
f [MHz]
1 2 3 4 5 6
Chirp BW Separation
Time
Amplitude
Time
Frequency
or
35 Mhz 6 Mhz
f [MHz]
100 375
f [MHz]
100 375
1300 MHz
7825 MHz
(VTS)
7600 MHz
(SMR)
100 - 375 MHz
1400 - 1675 MHz
9225 - 9500 MHz (VTS)
9000 - 9275 MHz (SMR)
9260 9301 9342 9383 9424 9465
9441.5
9447.5](https://image.slidesharecdn.com/ieeeatcradarsystemengineeringv3-151016034043-lva1-app6891/85/A-Tutorial-on-Radar-System-Engineering-48-320.jpg)
![76
Range Ambiguity
• The maximum unambiguous range: ,max
2 2
u
cPRT c
R
PRF
Page 2 of 4
Range: 5 NM
Transmit
Pulse 1
t = 0 Next pulse
Time needed for the pulse to hit the target: T = 31 µs
Time needed for the pulse to return to the antenna: T = 31 µs
Time needed between two pulses: T > 62 µs or PRF < 16.1 kHz (corresponding 2 x range, here 10 NM)
Target at 5 NM
t = 31 µs
Receive
Pulse 1
t = 62 µs
PRF [Hz]
1000
1500
2200
4000
8000
[km]
150
100
68.2
37.5
18.7
Max. range [NM]
81
54
36.8
20.2
10.1
300.000 km/s
300.000 km/s
Max. range =
c
2PRF
150.000
PRF
81.000
PRF
km NM
76](https://image.slidesharecdn.com/ieeeatcradarsystemengineeringv3-151016034043-lva1-app6891/85/A-Tutorial-on-Radar-System-Engineering-76-320.jpg)
![107
LUT
(Look-up
Table)
The difference in signal level
between 50% and 90%
fractile, is used to point out an
additional attenuation in the
LUT
- Att.
Signal Level
(90% - 50%)
Interval Frequency [%]
Frequency [%],
accumulated
0-15 8,6 8.6
16-31 11,7 20.3
32-47 18,0 38.3
48-63 11,7 50.0
64-79 1,6 51.6
80-95 5,5 57.1
96-111 4,7 61.8
112-127 4,7 66.5
128-143 5,5 72.0
144-159 3,1 75.1
160-175 3,9 79.0
176-191 5,5 84.5
192-207 3,9 88.4
208-223 3,9 92.3
224-241 3,1 95.4
240-255 4,7 100.0
Receiver Processing
• Range cells statistics](https://image.slidesharecdn.com/ieeeatcradarsystemengineeringv3-151016034043-lva1-app6891/85/A-Tutorial-on-Radar-System-Engineering-107-320.jpg)
A Tutorial on Radar System Engineering
- 1. Dr LEE Kar Heng Chief TBSS Group Ph.D, M.Eng, M.Sc, B.Tech(Hons), MIEEE Certified Teacher in Higher Education SEDA & TP RADAR SYSTEM ENGINEERING IEEE International Conference on Advanced Telecommunications Conference, Ho Chi Minh City, Vietnam, 2015
- 2. 2 • The speaker is thankful to TERMA for the use of TERMA Radar technical information in this tutorial • Terma has delivered 7 radars in Vietnam – 2 Surface Movement Radars: Tan Son Nhat International Airport and Noi Bai International Airport – 3 Vessel Traffic Radars: Port of Ho Chi Minh City – 2 Vessel Traffic Radars: Port of Hai Phong Acknowledgement
- 3. 3 Tutorial Objective • To understand the entire functionalities of radar systems: its components and operations
- 4. 4 Tutorial Outline Scan Pattern Generator Antenna Duplexer Waveform Generator Transmitter Receiver Signal Processor Data Extractor Data Processor Radar Display • A Typical Radar System
- 5. 5 Quick Review • RADAR- Radio Detection and Ranging • Theory of reflection, absorption and scattering • Higher frequency gives better result (???) • Information from radar: Range, height, direction, direction of motion, relative velocity
- 6. 6 • Target distance is calculated from the total time (tdelay) taken by the pulse to travel to the target and back to the radar • c = 3 x 108 m/s, speed of light Quick Review tdelay
- 7. 7 Quick Review Video Noise Noise & clutter Noise & clutter tdelay
- 8. 8 Quick Review Noise (not necessarily visible) Targets (land) Targets (vessels) Sea Clutter Rain VRM 63 km (34 NM) A weather radar will see rain clutter as information. A navigation radar will see rain clutter as noise.
- 10. 10 • Block diagram of a typical pulsed radar A Pulsed Radar System TX RXAntenna Motor Motor Controller Magnetron Modulator HV, PW Receiver Limiter LNFE IF Amplifier Video Ampl. STC Video Processing Power Supplies Encoder, ARP & ACP’s Control Wave Guide Circulator Interface Interface to external equipment
- 11. 11 A Pulsed Radar System • A typical radar system Antenna System Transceiver • Transmitter • Receiver • Plot Extractor • Tracker • Control Electronics • Interface Two transceivers provides redundancy and hot-standby
- 12. 12 A Pulsed Radar System • The Transceiver: WG SSPA WG Assy SSPA
- 13. 13 A Pulsed Radar System • The Transceiver – Waveguide Assembly: 13
- 14. 14 A Pulsed Radar System • The transmission: WG WG Coupler Limiter / STC Adapter Adapter Transmission from antenna SSPA Signal coming from SSPA enters the circulator through WG SSPA Signal passing the circulator cw and takes first exit Signal enters the antenna through the installed WG
- 15. 15 A Pulsed Radar System • The reception: WG WG Coupler Limiter / STC Adapter Adapter Reflections from targets are captured by the antenna RxTx Signal arrives coupler, a -50 dB signal out for measurement purposes Signal passing the circulator cw and takes first exit Signal enters the circulator through the installed WG RxTx Control RxTx Signal added through a -20 dB coupler - for calibration purposes Attenuation of the signal up to 40 dB Test port RxTx Signal passing the circulator cw and applied the RxTx module
- 16. 16 • The antenna receives the EM energy from the transmitter and radiates the energy into the free space Antenna System • An isotropic antenna radiates the energy in a spherical pattern • The energy is distributed equally in all directions 16
- 17. 17 Antenna System • In practice, the radiated energy is focused in a direction • The radiation pattern describes how the energy is radiated (or focused) • The characteristics of radiation pattern are beamwidth, gain and sidelobes The ability to focus the EM energy gives the gain of the antenna
- 18. 18 Antenna System • Radiation from a directional source • The energy is focused in a given directions • This allows the energy to travel further, hence a gain, G, compared to the isotropic source 18
- 19. 19 Antenna System • Coastal Surveillance and Vessel Traffic System radars are usually fan or inverse-cosecant-squared beams fan beam pattern Inverse-cosecant-square beam pattern
- 20. 20 Antenna System • A 21’ Slotted Waveguide Array Antenna
- 21. 21 Antenna System • Horn directs the EM energy and hence improves the antenna gain (1) • The polarization filter gives circular or horizontal polarization (3) • The antenna is protected by a radome (4) • The antenna is radiated by the slotted waveguide (2) Radome (front) Horn Polarization filterRF radiator (slotted waveguide) Radome (back) 1 2 3 44 1
- 22. 22 Antenna System • The beam pattern: beamwidth
- 23. 23 Antenna System • Antenna performance: Main Parameters: Frequency band 9.14 - 9.47 [GHz] VSWR 9.345 - 9.405 GHz ≤ 1.15 9.140 - 9.470 GHz ≤ 1.20 Gain ≥ 38 [dBi] Integrated Cancellation Ratio ≥ 15 [dB] Azimuth Pattern: Horizontal BW @ -3 dB ≤ 0.35 [º] Side lobe level ± 1.5º to ± 5º ≤ -28 [º] ± 5º to ± 10º ≤ -30 [º] Exceeding ± 10º ≤ -35 [º] Elevation Pattern: Elevation beam form Fan Vertical BW @ -3 dB ≤ 11 [º] Min. coverage @ -30 dB -18 [º] Tilt (fixed) -1.5 [º]
- 24. 24 Antenna System • For mechanically-steered antenna, the bearing information is obtained using encoder Antenna A B C A B C Direction (encoder)
- 25. 25 Antenna System Radome Encoder Assembly and Rotatory Joint Module Linear array Antenna Tx Rx Flared horn Connection box Power Encoder(s) Thermal sensors Encoder (s) Rotary joint Waveguide RF Flange Turning unit Gearbox Thermal sensors Motor Antenna unit Slotted waveguide (SWG)
- 26. 26 Antenna System • The encoder: ENCODER Stationary Waveguide Entry (to transceiver) Rotating Waveguide Entry (to Antenna) ENCODER INTERNAL
- 27. 27 Antenna System • The encoder: Channel A Channel A Channel B Channel B Channel N Channel N photodetector LED light source Rotating encoder disk, gray or Manchester coded generate the counting pulse Bipolar pulses (RS422)
- 28. 28 Antenna System • Whenever a stationary waveguide is to be connected to a rotating antenna, a rotating joint must be used • In radars, rotary joints connect transmitter and/or receiver to its rotating antenna • A circular waveguide is normally used in a rotating joint Stationary Waveguide Entry (to transceiver) Rotating Waveguide Entry (to Antenna)
- 29. 29 Control • It consists of a timing control that generates the synchronization timing signals Timing Control Modulator and Transmitter Receiver Signal Processor Duplexer Antenna To other modules Scan Pattern Generator (RPM, Beam Control, …)
- 30. 30 Modulator • The modulator produces a high power DC pulse to the transmitter • A modulated signal is generated and sent to the antenna by the modulator and transmitter block • A train of narrow rectangular shaped pulses modulating a sine wave carrier is transmitted Pulse width Pulse Repetition Time (PRT) Rest Time (Listening) Radar Carrier Frequency 30
- 31. 31 Magnetron Transmitter • The transmitter is a high power oscillator, e.g. a magnetron • The magnetron generates high power RF wave • Transmitted pulse is high power, short duration • The EM wave is sent to the duplexer via waveguide (transmission line) • Transmitter remains silent during the listening period Magnetron
- 32. 32 Magnetron Transmitter • The two main limitations of magnetron are – Limited average power – Poor ability to detect moving targets in heavy clutter • The peak power of several MW can be produced by magnetron, but the average power is limited to 1 -2 kW • The pulse width limitation prevents the magnetron from being used with pulse compression where frequency or phase modulation is difficult • Magnetrons are noisy outside the operating frequency
- 33. 33 Marine Radar Magnetrons • The magnetrons have been used extensively in civil marine radars • They are compact and can generate peak powers between 3 and 75 kW with average powers from a few W to a few 10s of W • They offer reliability which sea-goers require • Marine radar operates at a fixed frequency within the band 9.38 GHz to 9.44 GHz
- 34. 34 Marine Radar Magnetrons • A RF assembly that houses both the transmitter and receiver Magnetron Circulator LNFE TR Limiter IF AMP Assembly
- 35. 35 The Solid-State Transmitter • Solid-state RF power generation is becoming more common presently in VTR and marine radars • It is designed with transistor amplifiers (BJT or FET) • One stage transistor amplifier is low power and low gain but it operates with low voltages and has high reliability • To increase the power, parallel configuration and multistage transistor amplifiers are used
- 36. 36 The Solid-State Transmitter • The advantages of Solid State Transmitter – Individual solid-state devices have long MTBF – Maintenance is easy with modular design and construction of solid state – Broad bandwidth – No cathode heating required (no need for high voltage and warm up time) – No pulse modulator required – Solid-state transistor amplifiers have low noise and good stability
- 37. 37 The Solid-State Transmitter • Advantages of Solid-State radars over magnetron radars PARAMETERS SOLID-STATE MAGNETRON Maintenance Low High – annual magnetron replacement Remote Control and Monitoring Fully digital and remote controller Requires digital interface for full remote control Built-in-Test (BIT) Extensive and fully remote accessible Limited MTBF 50,000 hours 3,000 hours Antenna Speed Electronically selectable, high speed scanning gives improved track quality Standard 24 rpm, requires motor and gear replacements
- 38. 38 The Solid-State Transmitter • Advantages of Solid-State radars over magnetron radars PARAMETERS SOLID-STATE MAGNETRON Antenna Tilt Yes No Emitted Power Density Low power mode for short range use and operations near hot ordinance High Variable Frequency Yes – electronic control No Start-Up Instantaneous operation Warm up time Spares Low High (replace magnetrons) Frequency diversity (improved performance) Yes No Doppler processing Yes No
- 39. 39 The Solid-State Transmitter • Meeting IEC 60963-1/62388 Requirements Height (m) RCS (m2) IEC 60936-1 (nm) IEC 623880 (nm) Solid-State (nm)* 60 50000 20 20 24.2 6 5000 7 8 12.7 3 2500 --- 6 10.4 10 50000 7 11 15.6 5 1800 --- 8 11.6 4 7.5 --- 5 7.8 3.5 10 2 4.9 7.6 3.5 5 --- 4.6 7.2 2 2.5 --- 3.4 5.8 1 1 --- 2 4.1
- 40. 40 The Solid-State Transmitter • The parameters of a solid-state radar PARAMETERS X-BAND S-BAND Model 1 Model 2 Overall length 3.7 m 5.5 m 3.9 m Turning circle diameter 3.8 m 5.6 m 4 m Frequency band 9.22 – 9.44 GHz Gain 32.7 dB 34.5 dB 27.5 dB Horizontal beamwidth 0.7 0.45 2 max. Vertical beamwidth 2 2 Horizontal sidelobes within 10 -26 dB At least -28 dB dowm Horizontal sidelobes outside 10 -33 dB At least -35 dB down
- 41. 41 The Solid-State Transmitter • The detection performance of the X-band radar: Antenna Height Target Type Modeled as fluctuating point target Detection and Tracking distance (nm) RCS (m2) Height (m) Clear Weather 10 mm/h Rain 50 m AMSL 1 1 1 m AMSL 10/8.25 (SS4) ---- 2 3 2 m AMSL 12/11.23 (SS5) 9/10.64 (SS 5) 3 10 3 m AMSL 14/13.3 (SS6) 12/12.71 (SS6) 4 100 5 m AMSL 17/16.29 (SS7) 15/15.83 (SS7) 5 1000 8 m AMSL 20/19.2 (SS8) 18/18.71 (SS8) • The results are obtained from CARPET based on PFA = 10–6 and PD = 80%
- 42. 42 The Solid-State Transmitter • A Typical Transmitter Design based on SSPA SSPA WG Assy RxTx BP BP BP BP Combiner 1300 MHz 7825 MHz (VTS) 7600 MHz (SMR) 1300 MHz 7825 MHz (VTS) 7600 MHz (SMR) 9.225 - 9.5 GHz (VTS) 9.0 - 9.275 GHz (SMR) TxRAM/FPGA DAC / DDS DAC / DDS BP BP AttenuationAttenuation RxTx Control 100 - 375 MHz (low) 100 - 375 MHz (high)
- 43. 43 A Typical Solid-State Transmitter • The design of a solid-state transmitter: Power Amplifier Power Amplifier Module 1 Module 2 Powersplitter Poweradder Incomingsignal Transmittedsignal
- 44. 44 A Typical Solid-State Transmitter • The solid-state power amplifier (SSPA) amplifies the signal before transmission • The transmitted power ranges from 50 W (short range) to 200 W (long range) typically • The required power is constructed using multi- stage and parallel configuration of single stage power amplifiers PA module In Out 8 W power transistor 50 W power amplifier
- 45. 45 A Typical Solid-State Transmitter • The typical solid-state power amplifier 50 W 200 W
- 46. 46 A Typical Solid-State Transmitter • The degradation performance 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0% 25% 50% 75% 100% Percentage of power transistors in failure Available SSPA power Output power Free space range
- 47. 47 Radar Waveform • The carrier is modulated using a scheme that is similar to that used in communication systems – ASK or ON-OFF AM Pulse width, t (TX) Pulse Repetition Time (PRT) Rest Time (Listening) (RX) Radar Carrier Frequency
- 48. 48 Radar Waveform • The Chirp Pulse: Time Amplitude Time Frequency f [MHz] 1 2 3 4 5 6 Chirp BW Separation Time Amplitude Time Frequency or 35 Mhz 6 Mhz f [MHz] 100 375 f [MHz] 100 375 1300 MHz 7825 MHz (VTS) 7600 MHz (SMR) 100 - 375 MHz 1400 - 1675 MHz 9225 - 9500 MHz (VTS) 9000 - 9275 MHz (SMR) 9260 9301 9342 9383 9424 9465 9441.5 9447.5
- 49. 49 Radar Waveform • High resolution radar – short transmission pulses are required – Short transmission pulse requires high transmission power for long distance (B = 1/t) – Short transmission pulse gives large bandwidth (receiver noise must be considered) • Best – Long pulse for long distance – Short pulse width for high resolution – Small bandwidth for large dynamic range
- 50. 50 Radar Waveform • The signal flow:
- 51. 51 Radar Waveform • Pulse Compression Every little part of the wave represents a specific frequency Low frequencies are slowed down High frequencies are speeded up Processing
- 52. 52 Radar Waveform • Pulse Compression Transmitted chirp Received chirp
- 53. 53 Radar Waveform • Pulse Compression f1f2f3f4 Σ Σ Σ f1 f2 f3 f4 Σ Bandpass Delay Summation
- 54. 54 Radar Waveform • Pulse Compression f1f2f3f4 f1 f2 f3 f4
- 55. 55 Radar Waveform • Pulse Compression Σ Σ Σ
- 56. 56 Radar Waveform • Pulse Compression – cross correlation
- 57. 57 Radar Waveform • Pulse Compression – cross correlation
- 58. 58 Radar Waveform • Pulse Compression – time side lobes Antenna
- 59. 59 Radar Waveform • Pulse Compression – windowing
- 60. 60 Radar Waveform • Pulse Compression – windowing
- 61. 61 Radar Waveform • Pulse Compression • Requirement – Range resolution – 30 m – Pulse compression ratio – 75 • The compressed pulse duration • The compressed bandwidth s c R t resolution compressed 2.0 103 3022 8 MHz5 102.0 3011 6 compressedt BW
- 62. 62 Radar Waveform • Pulse Compression • Requirement – Range resolution – 30 m – Pulse compression ratio – 75 • The required transmission pulse width • If the SSPA gives 200W, the virtual transmitted power kW1575200 PCRPP SSPAvirtual sPCRtcompressed t 1575102.0 6
- 63. 63 Radar Waveform • Radar video with pulse compression
- 64. 64 Radar Waveform • Radar video without pulse compression
- 65. 65 Radar Waveform • For a single pulse, the maximum unambiguous range, Ru,max, is determined by the PRF (1/PRT), • High PRF is unambiguous in Doppler but highly ambiguous in Range since it meets the Nyquist sampling criteria for Doppler shift of all targets design to detect but there is little time between pulses for ranging PRF c R R c PRF u u .22 max, max,
- 66. 66 Radar Waveform • Medium PRF radar may be ambiguous in both Doppler and range since it samples too fast for echoes from long range but too slow to Nyquist sample the Doppler shift of all targets • Medium PRF however has the best of both worlds, a compromise performance between unambiguity in Doppler and range • Low PRF is unambiguous in range but high ambiguous in Doppler since it waits until the last transmitted pulse arrives before the next transmission Low PRF t PRT = 1/PRF f 0 PRFPFF High PRF t f 0 PRFPFF
- 67. 67 Radar Waveform • Different PRF is used in different application such as Low PRF or Medium PRF is suitable for detection of vessels while High PRF is used in detecting air targets • Careful selection of PRF will also result in better tracking performance since one must be able to detect a target before tracking it • Mixture of pulse durations enhances the performance
- 68. 68 Radar Waveform • Time duration variations of chirps: Rx Tx Rx Rx Rx Tx Tx Tx Tx Rx Tx Rx Sweep n Sweep n+1 Sweep n+2 Sweep n+3 Sweep n+4 Sweep n+5 t Instrumented range Minimum range Antenna rotation S M L Sweep n Sweep n+1 Sweep n+2 Sweep n+3 Sweep n+4 Sweep n+5 Depending on range required and application, three combinations of chirps can be used: 1. combination: SHORT, MEDIUM and LONG
- 69. 69 Radar Waveform • Time duration variations of chirps: Rx Tx Rx Rx Rx Tx Tx Tx Tx Rx Tx Rx Sweep n Sweep n+1 Sweep n+2 Sweep n+3 Sweep n+4 Sweep n+5 Instrumented range Minimum range Antenna rotation S M Sweep n Sweep n+1 Sweep n+2 Sweep n+3 Sweep n+4 Sweep n+5 2. combination: SHORT and MEDIUM
- 70. 70 Radar Waveform • Time duration variations of chirps: Rx Tx Rx Rx Rx Tx Tx Tx Tx Rx Tx Rx Sweep n Sweep n+1 Sweep n+2 Sweep n+3 Sweep n+4 Sweep n+5 t Instrumented range Minimum range Antenna rotation S Sweep n Sweep n+1 Sweep n+2 Sweep n+3 Sweep n+4 Sweep n+5 3. combination: SHORT only
- 71. 71 • The receiver amplifies the radar returns and prepares them for signal processing • Extractor of target information from the returns is performed by the signal processor, tdelay is determined for each detected target • Target distance is calculated from the total time (tdelay) taken by the pulse to travel to the target and back c = 3 x 108 m/s, speed of light 1 s = 300,000,000 m = 300,000 km 1ms = 300 km Target Range
- 72. 72 Target Range The PRF determines how often the radar transmits (PRF = pulses/s = 1/PRT or 1/PRI) and the maximum range of the system (PRT = Pulse Repetitive Time, PRI = Pulse Repetitive Interval) Transmitted pulses Pulse travels 150 km in 0.5 ms Maximum range = 0.25 ms (75 km) Echo needs 0.25 ms to return Transmitted pulses Pulse travels 300 km in 1 ms Maximum range = 0.5 ms (150 km) Echo needs 0.5 ms to return PRF = 2 kHz PRT = 0.5 ms PRF = 1 kHz PRT = 1 ms 1 ms
- 73. 73 Average Power • In each cycle (PRT), the radar only radiates from t sec (known as pulse width or PW) • The average transmitted power is where Pt = peak transmitted power and PRF = Pulse Repetition Frequency, . .av t tP P P PRF PRT t t 1 PRF PRT
- 74. 74 Range Ambiguity • The range that corresponds to the 2-way time delay is the radar unambiguous range, Ru • Consider detection of 1 target at R1 in two separate transmissions Transmitted Pulses Received Pulses Pulse 1 Pulse 2 echo 1 echo 2 PRT t tdelay tdelay Ru (R ) 1 R2
- 75. 75 Range Ambiguity • Echo 1 is the return from target at range R1, • Echo 2 is the return from the same target at range R1, from the 2nd transmission • Echo 2 can also be taken as an echo from a different target from the 1st transmission 1 2 delayct R 2 1 2 delayct R R 2 2 delayc PRT t R ERROR!!!
- 76. 76 Range Ambiguity • The maximum unambiguous range: ,max 2 2 u cPRT c R PRF Page 2 of 4 Range: 5 NM Transmit Pulse 1 t = 0 Next pulse Time needed for the pulse to hit the target: T = 31 µs Time needed for the pulse to return to the antenna: T = 31 µs Time needed between two pulses: T > 62 µs or PRF < 16.1 kHz (corresponding 2 x range, here 10 NM) Target at 5 NM t = 31 µs Receive Pulse 1 t = 62 µs PRF [Hz] 1000 1500 2200 4000 8000 [km] 150 100 68.2 37.5 18.7 Max. range [NM] 81 54 36.8 20.2 10.1 300.000 km/s 300.000 km/s Max. range = c 2PRF 150.000 PRF 81.000 PRF km NM 76
- 77. 77 Range Ambiguity The illustration of range ambiguity using lattice diagram: t PRF 3.75 kHz, T = 266.7 µs 30 km T = 266.7 µs Tx pulse n Tx pulse n+1 Tx pulse n+2 Tx pulse n+3 40 km T = 266.7 µs T = 266.7 µs T = 266.7 µs RANGE 40 km Tx pulses Echoes 30 km Echoes 60 km Range 60 km 200 µs 200 µs 200 µs 200 µs 133.3 µs 133.3 µs 133.3 µs
- 78. 78 Range Ambiguity Falsetarget Truetarget T0 t-n t t-n t t-n t t-n t T0Sweep 1 T0Sweep 2 T0Sweep 3 T0Sweep 4 Falsetarget Truetarget T0AND T0ADD
- 79. 79 Range Ambiguity • Staggered PRF is used to avoid “jamming” or interference from other radars’ transmitting and “second time around” • The change of repetition frequency does that the radar on a pulse to pulse basis can differentiate between returns from itself and returns from other radar systems with same frequency. T = 1 PRF Without stagger PRF: 1 kHz = 1 ms T = 1 msT = 1 ms T = 1 ms T = 1 PRF With stagger 8% PRF: 1 kHz + 8% = 1.08 ms T = 1 PRF - 2% = 0.98 ms T = 1 PRF + 4% = 1.04 ms T = 1 PRF - 8% = 0.92 ms
- 80. 80 Range Ambiguity T0 Falsetarget t-n t-m t-p t-q Truetarget t t t t Falsetarget Truetarget T0 T0 T0 T0 Sweep 1 Sweep 2 Sweep 3 Sweep 4 AND T0 ADD T0
- 81. 81 Range Resolution • Range resolution, R, is the radar ability to detect targets in close proximity as 2 distinct targets • 2 close proximity targets must be separated by at least R to be completely resolved in range • Consider 2 targets located at ranges R1 and R2, corresponding to time delays t1 and t2 respectively, the difference between the 2 ranges is 2 1 2 1 2 2 c c R R R t t t
- 82. 82 Range Resolution • To distinguish the 2 targets, they must be separated by at least 1 pulse width t, where B = radar bandwidth 2 2 c c R B t Received Pulses return target 1 c return target 2 t ct target 1 target 2 ct R R1 2
- 83. 83 2 2 c c R B t Range Resolution Range resolution: Pulse width = 1 µs, length of pulse flying through the air = 300 mDistance is half of 300 m = 150 m For a 150 ns pulse, the range resolution, m5.22 2 10150103 2 98 tc R Two targets must be separated by at least 22.5 m so that they can be detected as two distinct targets by the radar with a pulse width of 150 ns.
- 84. 84 Range Resolution PW: 1 μs Length: 300 m Range resolution: 150 m 150 m 120 m PW: 250 ns Length: 75 m Range resolution: 37.5 m 50 m 30 m PW: 50 ns Length: 15 m Range resolution: 7.5 m 10 m 7 m
- 85. 85 • The number of wavelengths contained in the two way path between the radar and the target, • Total phase shift, • Radar is able to give radial velocity of a moving target from Doppler Effect • Doppler effect causes a shift in frequency of the received echo signal from a moving target • Doppler frequency shift • Let R be the Range of the target Doppler Effect RADAR TOWER INBOUND ECHO RADAR ANTENNA TRANSMIT PULSE OUTBOUND ECHO 2R n 4 2 R n
- 86. 86 • When the target is moving, R and φ change continuously • The rate of change of φ is angular frequency where vr = radial velocity of the target towards the radar • The Doppler frequency shift, where Doppler Effect 44 2 r d d vd dR f dt dt 22 r or d v fv f c cosrv v
- 87. 87 Duplexer • The duplexer is a waveguide switch • It passes the transmitted high-power pulses to the antenna and the received echoes from the antenna to the receiver • Duplexer switches automatically based on the timing control signal
- 88. 88 Receiver • The receiver picks up the target signal from the received signal, which includes noise and interference • Performance requirement: – To detect the targets with highest probability of detection (PD) – To minimize the false alarm (classifying noise, clutter or interference as target) (PFA) • PD and PFA are related to the SNR, stronger signal power over the noise power gives better performance
- 89. 89 Receiver Time Receivedpower Threshold Target returns Random noise • 3 out of the 4 targets detected are real targets, the PD = 75% • If the no. of noise spikes above the threshold is 1 out of 50, the PFA = 2%
- 90. 90 Radar Detection • Radar detection is a binary decision problem and the process is statistical
- 91. 91 Radar Detection • It is necessary to decide the presence of a target when – The target is usually embedded and corrupted by random noise from the atmosphere, thermal, … – The target RCS is also statistical • Consider the following radar system:
- 92. 92 Radar Detection • The radar transmits and the detector output is measured 100 times at a fixed time interval without backscattering • The 100 samples are tabulated using a histogram • The histogram is a discrete probability function with finite probability interval and limited number of measurements V Relative Frequency, n 0 – 0.1 2 0.1 – 0.2 10 0.2 – 0.3 16 0.3 – 0.4 22 0.4 – 0.5 19 0.5 – 0.6 13 0.6 – 0.7 8 0.7 – 0.8 5 0.8 – 0.9 3 0.9 – 1.0 1 > 1.0 0
- 93. 93 Radar Detection • The discrete probability histogram, 0.02 0.1 0.16 0.22 0.19 0.13 0.08 0.05 0.03 0.01 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 No. of Samples, N = 100 V n N 1 V n N 0S
- 94. 94 Radar Detection • As the interval approaches 0, the discrete time histogram becomes a continuous time function, called Probability Density Function PDF for S/N = 0 (no target)
- 95. 95 Radar Detection • The voltmeter is replaced by a threshold detector and indicator where when 0 when o T T V V V V V V
- 96. 96 Radar Detection • As there is no target, any measured voltage that is greater the threshold gives a false alarm Single pulse Probability of False Alarm
- 97. 97 Radar Detection • The probability of false alarm (PFA) depends on the threshold • The threshold can be set to give a desired PFA, for instance, PFA = 0.1 (this means that the shaded area is 10% of the total area under the PDF curve) • The measurements can be carried with S/N = 1, S/N = 2, S/N = 4 for different targets
- 98. 98 Radar Detection • The PDFs for different signal strengths Single pulse PDFs for different S/N , , , T D T D FA T V S S S P V P P P V V p V dv N N N
- 99. 99 Radar Detection • The area under the PDF curve for S/N > 0 give the probability of detection (PD) for the required PFA = 0.1 • For a different PFA, the PD will change when VT changes For a smaller allowed PFA, the PD is smaller for a given S/N
- 100. 100 Ordered statistics Page 1 of 2 4 2 11 14 0 2 16 6 3 9 10 4 17 7 12 11 5 8 1 13 13 15 11 3 5 16 9 10 12 11 5 8 14 11 5 14 4 7 11 9 10 16 4 0 17 5 12 17 15 5 0 - 2 3 - 5 6 - 8 9 - 11 12 - 14 15 - 17 Interval Frequency 5 12 5 12 8 8 50 Acc. frequency in % 10% 34% 44% 68% 84% 100% Frequency in % 10% 24% 10% 24% 16% 16% 100% Receiver Processing • Ordered Statistics
- 101. 101 Ordered statistics Page 2 of 2 0 - 2 3 - 5 6 - 8 9 - 11 12 - 14 15 - 17 Interval Frequency 5 12 5 12 8 8 Acc. frequency (%) 10% 34% 44% 68% 84% 100% 0 - 2 3 - 5 6 - 8 9 - 11 12 - 14 15 - 17 Interval Receiver Processing • Ordered Statistics
- 102. 102 u t PD = 20% (1 target of 5) PD = 80% (4 targets of 5) PFA = Too high (threshold too low) PFA = Constant (CFAR) Receiver Processing • Constant False Alarm Rate (CFAR) Adaptive Threshold
- 103. 103 u t PPA = Constant, ex. 10-6 u t Receiver Processing • Received signal
- 104. 104 0 m End of range 0 m End of range Range cell containing 8 bit video information 0 m End of range Ordered statistics Ordered statistics Ordered statistics Ordered statistics Ordered statistics .....and so on Receiver Processing • Range cells
- 105. 105 Cell Level Cell Level Cell Level Cell Level 1 38 33 99 65 132 97 45 2 52 34 66 66 154 98 82 3 60 35 112 67 136 99 37 4 30 36 98 68 100 100 41 5 45 37 85 69 165 101 56 6 63 38 125 70 143 102 47 7 61 39 100 71 154 103 62 8 38 40 105 72 134 104 61 9 43 41 127 73 112 105 35 10 60 42 75 74 143 106 80 11 51 43 92 75 153 107 17 12 37 44 95 76 154 108 15 13 44 45 81 77 199 109 31 14 39 46 115 78 167 110 32 15 51 47 220 79 182 111 34 16 42 48 251 80 176 112 14 17 6 49 238 81 165 113 32 18 8 50 243 82 181 114 55 19 16 51 243 83 200 115 31 20 20 52 232 84 210 116 42 21 15 53 222 85 179 117 13 22 29 54 249 86 172 118 27 23 36 55 228 87 213 119 54 24 12 56 241 88 203 120 22 25 24 57 190 89 176 121 30 26 14 58 237 90 186 122 57 27 21 59 220 91 199 123 43 28 30 60 201 92 105 124 52 29 18 61 247 93 117 125 34 30 25 62 160 94 38 126 8 31 32 63 135 95 55 127 15 32 82 64 143 96 32 128 3 0 50 100 150 200 250 300 1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106 113 120 127 Cell BitLevel Bit Level Floating window covering 128 cells Receiver Processing • Range cells statistics
- 106. 106 Interval Frequency 0-15 11 16-31 15 32-47 23 48-63 15 64-79 2 80-95 7 96-111 6 112-127 6 128-143 7 144-159 4 160-175 5 176-191 7 192-207 5 208-223 5 224-241 4 240-255 6 Diagram showing the intervals and the frequency in each. Receiver Processing • Range cells statistics
- 107. 107 LUT (Look-up Table) The difference in signal level between 50% and 90% fractile, is used to point out an additional attenuation in the LUT - Att. Signal Level (90% - 50%) Interval Frequency [%] Frequency [%], accumulated 0-15 8,6 8.6 16-31 11,7 20.3 32-47 18,0 38.3 48-63 11,7 50.0 64-79 1,6 51.6 80-95 5,5 57.1 96-111 4,7 61.8 112-127 4,7 66.5 128-143 5,5 72.0 144-159 3,1 75.1 160-175 3,9 79.0 176-191 5,5 84.5 192-207 3,9 88.4 208-223 3,9 92.3 224-241 3,1 95.4 240-255 4,7 100.0 Receiver Processing • Range cells statistics
- 108. 108 Noise Sea 50% 90% 50% 90% 256 (total) 50% 90% 25 Delta values (value at 90% - value at 50%) are used to point out a value in the LUT - a guesstimate of the level in the upper 10% Delta values (value at 90% - value at 50%) are used to point out a value in the LUT - a guesstimate of the level in the upper 10% Receiver Processing • Range cells statistics
- 109. 109 90% 50% Δ = Hi Δ = Lo 50% 90% Sea Δ = Hi 99.9999% 50% 90% Noise Δ = Lo 99.9999% Receiver Processing • Range cells statistics
- 110. 110 50% 90% Sea Δ = Hi 99.9999% 50% 90% Noise Δ = Lo 99.9999% Δ value The delta value is used to guesstimate the value at 99.9999%, PFA = 10-6 . The value of the attenuation to obtain this, is fetched from the LUT and therefore the attenuation depends on the distribution curves Δ value LUT Δvalue 90% CFAR: 10-6 Receiver Processing • Range cells statistics
- 111. 111 Noise Clutter Noise Signal consisting of noise and sea clutter Attenuation working OK and the clutter is attenuated to the level of the noise. Undercompensated - the clutter is not sufficiently attenuated and will make a concentration of clutter on the radar image. Overcompensated - the clutter is attenuated too hard and will make a "hole" in the noise on the radar image. Receiver Processing • Range cells statistics
- 112. 112 Page 11 of 11 Receiver Processing • CFAR effect:
- 113. 113 Average is stored in weep n+3 For the next integration cycle sweep n+1 will be sweep n Sweep n+3 Sweep n+2 Sweep n+1 Sweep n Video Noise Receiver Processing • Sweep Integration:
- 114. 114 Sweep n Sweep n+1 Sweep n+2 Sweep n+3 ADD ADD / 4 Receiver Processing • Sweep Integration:
- 115. 115 0 100 200 300 400 500 0 2.5 5 7.5 10 12.5 15 14.686 2.19 10 3 single0i single1i 4 single2i 8 single3i 12 4990 i 4 sweeps 4 sweeps integrated gives an improved S/N 0 100 200 300 400 500 4 5 6 7 8 9 10 9.773 5.793 inco_inti 4990 i Receiver Processing • Sweep Integration:
- 116. 116 Receiver Processing • Sweep Integration:
- 117. 117 Receiver Processing • Scan Correlation – The radar performs sliding window scan-to-scan correlation for each range-azimuth cell to provide clutter discrimination – This is done to discriminate between clutter and targets that are of interest to the operator
- 118. 118 Scan Correlation • One channel performs sliding window scan-to-scan correlation over 3 consecutive scans to discriminate between clutter and extremely small targets with speeds up to e.g. 8 knots - the actual speed limit is determined by the antenna rotation speed, the pulse width and the range • A second channel performs sliding window scan-to-scan correlation over 2 consecutive scans in order to discriminate between clutter and small targets with speeds up to e.g. 16 knots - the actual speed limit is also here determined by the antenna rotation speed, the pulse width and the range • A third channel without scan-to-scan correlation to detect targets of medium and large size (RCS) at any speed Receiving Processing
- 119. 119 Receiving Processing • Scan Correlation
- 120. 120 Receiving Processing • Sweep Integration: Gate signal No gate signal AND Gate signal No gate signal AND 1 3 5 7 92 4 6 8 1 0Scan n-2 1 3 5 7 92 4 6 8 1 0Scan n-1 3 s 1 3 5 7 92 4 6 8 1 0 Clutter 1 3 5 7 92 4 6 8 1 0Scan n 3 s Target Returned echo (PW = 500 ns) Resolution cells (10 x 7.5 m) Threshold Level Target Returned echo (PW = 500 ns) Resolution cells (10 x 7.5 m) Threshold Level
- 121. 121 ANDAND 1 3 5 72 4 6 8Scan n-2 1 3 5 72 4 6 8Scan n-1 3 s 1 3 5 72 4 6 8Scan n 3 s Gate signal Receiving Processing • Sweep Integration:
- 122. 122 A Typical Tracking Radar System • The receiver decides that an object has been detected (signal strength > threshold) • The signal processor will determine the presence of real targets and rejects the unwanted returns
- 123. 123 A Typical Tracking Radar System • The data extractor will determine the target measurements such as range, azimuth and/or elevation (2D or 3D)
- 124. 124 A Typical Tracking Radar System • The data processor will perform the association, tracking and prediction task and maintains the target database • Echo – a group of coherent detections within the same sweep • Plot – a group of echoes within the same radar scan correlated in range and bearing in accordance to some pre-defined criteria such as center of gravity, peak amplitude, peak size, …
- 125. 125 A Typical Tracking Radar System • Tag/ID – an identification generated and assigned to a target • Overlay – a group of maps, symbols, navigation channel/pathway and text that are presented on radar display • Track – a sequence of kinematic state (position, speed, course, …) estimate of a target based on past plots
- 126. 126 A Typical Tracking Radar System • A typical radar with tracker is made up of tracking module/algorithm, display, scan conversion and user interface • The exchange of data is achieved via a local area network (LAN) LAN AREA NETWORK
- 127. 127 A Typical Tracking Radar System • The processors are connected to the system bus or network where radar input signals (ACP, ARP) and videos (targets, clutters) are processed and shared • The radar videos are packaged in LAN message protocol for sharing and further processing • The target echoes are identified as plots and tracking process is initiated • The tracking information is then distributed via the LAN
- 128. 128 A Typical Tracking Radar System • A typical radar data distribution over network Video, plots, tracks, BITE, control LAN RADAR TRANSCEIVER AND PROCESSOR 3rd PARTY CONTROL AND COMMNAND SYSTEM RADAR DISPLAY AND WORKSTATION RADAR SERVICE TOOL
- 129. 129 A Typical Tracking Radar System • Data interface and distribution RADAR TRANSCEIVER TRACKING MODULE Radar Video LAN Own speed Position Heading Map Control equipment Monitoring equipment Display 3rd Party Systems TracksTrails
- 130. 130 A Typical Tracking Radar System • Usually, extractor and tracker are housed under one single module Data Extractor Data Processor (Tracker) Plots Settings Radar Video Platform and Navigation Data Map Data Status Tracks Plot Position External Tracks
- 131. 131 Radar Scan Conversion • The radar scan converter receives raw radar video and converts it into a format for raster scan display • The radar interface takes in – video and antenna signal from the radar – the radar input gain and
- 132. 132 Radar Scan Conversion • A surveillance radar supplies its measured data in polar coordinates, i.e. in range-azimuth format (r,b) • Radar scan conversion involves the transformation of data in a range-azimuth format to an x-y format for a raster-scan display
- 133. 133 Radar Scan Conversion • The conversion is carried out using x = rsinb + Xc and y = rcosb + Yc where (Xc, Yc) is the radar center • The radar stores its raw data into a table called Polar Store (e.g a 256K cells) • The table columns represent all possible measurable range steps • Each table row represents a complete pulse period, which took place in a certain azimuth angle • The first line is the azimuth angle of 0°, the north direction
- 134. 134 Radar Scan Conversion • The radar interface will also accept the existing azimuths (2048 – 11-bit antenna word) per 360 • The actual acquired data in the form of rho-theta is stored in the display frame stores (e.g. 2048 by 2048) • The scan conversion algorithm handles the 2048 by 2048 resolution display in real time up to 60 r.p.m. antenna rotation rate • The scan conversion process is controllable • General graphics drawing capability is provided for flight/navigational plan and mask definition
- 135. 135 Radar Scan Conversion • Scan conversion can also be performed in several windows • The display controller graphics accelerator of the display card is supported by at least 2 GB of RAM to provide exceptional flexibility for generating combined graphics and radar video and with an output resolution of up to say 1600 by 1280 • The display shall consists of symbols and targets layer, radar video layer which fades and become transparent and maps and charts layer
- 136. 136 Plot Extractor • A radar plot is a group of connected range-azimuth cells whose measured signal strength exceeds a defined threshold • A plot is displayed which the video signal strength is larger than the threshold • Technique such as STC (Sensitivity Time Control) improves the target detection by suppressing the echoes nearby the radar
- 137. 137 Plot Extractor • In ideal situation, every target (wanted or unwanted) illuminated by the radar beam during the present sweep should result in only one echo • The plot extractor processes the radar data produced by the radar input to generate echoes every sweep by identifying echoes that have a size, shape and signal strength that is consistent with a valid return
- 138. 138 Plot Extractor • Plot extractor is software application that analyses radar video and detects potential targets • Processing is based on three main phases: – clutter suppression – adaptive thresholding – plot extraction • Clutter suppression can be based on Clutter Map Constant False Alarm Rate (CFAR) algorithm • Adaptive thresholding implemented can be Cell Averaging CFAR (CA-CFAR) detection • Plot extraction is detection of target-like shapes among video samples that exceed the threshold using standard m-of-n separation criterion
- 139. 139 Plot Extractor • Plot Extractor and radar input is direct (not TCP/IP) • Since Plot Extractor is the only component that requires high sample rate, it is optimal to place it on the same machine as the signal source • Another consumer of raw video samples is Radar Display • Since Radar Display requires lower sample rates, Plot Extractor also performs downsampling of the video before streaming it on the network
- 140. 140 The Tracking Process • A tracking process is generally made up of 3 stages namely, Initiation, Updating and Termination
- 141. 141 The Tracking Process • A good tracker will be able to provide better detection of highly maneuvering small targets
- 142. 142 The Tracking Process - Initiation • When a target is acquired, the initiate position (Cartesian coordinates) is taken from the tracker ball (some call it order marker) or generated by processor • The radar return defined by range and bearing (polar coordinates)
- 143. 143 • The conversion from polar to Cartesian coordinates is carried out every antenna scan, when a track is confirmed, the target speed and course can be calculated by the data processor The Tracking Process - Initiation
- 144. 144 • The initiation process Predicted position Track Radial acceleration Tangential acceleration Minimum speed Maximum speed The Tracking Process - Initiation
- 145. 145 • In order to associate correct plots to correct tracks, false alarms must be minimized, one conventional way is to correlate plots from more than 1 scan • The antenna is divided into several azimuth sectors, plots received from, say, 2 previous scans (e.g. N-1 and N-2) are stored in accordance to the sectors they are detected • The plots from current scan are then compared to these stored plots, the decision criteria for a successful correlation can be 2 out of 3 or generally, m-out-of-n The Tracking Process - Initiation
- 146. 146 • Consider a plot PN in sector S of antenna scan N, an initiation window will be opened at this plot position, a search is then made in N-1 plot database to find a plot within this window The Tracking Process - Initiation
- 147. 147 • Assuming only plots in sectors S-1, S and S+1 are search (for minimized comparison time) and that a plot PN-1 is found, then another search is carried out in N-2 plot database The Tracking Process - Initiation
- 148. 148 • If the search is successful in N-2 plot database then the primary track initiation is successful, however, if there is no plot in N-2 plot database, then the primary track initiation can also be considered successful if the decision criteria is 3- out-of-2 The Tracking Process - Initiation
- 149. 149 • The available plots are then used to calculate the target position in x-y coordinates, the speed vector and the predicted next position (by filtering) • They are also used to determine the quality of the track (centroid) and subsequently the gate size Centroid is of a target is defined as the value of independent variable (in time) where the area under the target spectrum to the right equals to the left The Tracking Process - Initiation
- 150. 150 • Given a plot at radar scan N, it is necessary to determine the shade (usually not implemented) and size of the correlation gate in order to capture the plot at scan N+1, the gate is usually defined in terms of range and azimuth The Tracking Process - Initiation
- 151. 151 • The prediction process With good predictions the search window gets smaller With bad predictions the search window gets bigger The Tracking Process - Initiation
- 152. 152 • Correlation window eliminates the unlikely plot-to- track pairings and hence reduce unnecessary computation • During the initial acquisition, usually the 1st 2 scans, the processor does not have sufficient knowledge of the target’s course and speed, the gate is larger to increase the match probability • After several scans, the target’s motion is better known, the gate size reduces, the gate size is determined by the radar measurement error and possible maneuvering The Tracking Process - Initiation
- 153. 153 • After the new track is initiated and vector generated, track updating is necessary to update the track with correct plots obtained so as to update current track information (position, speed, course) and predict future position • The 1st task involves comparing the incoming plots with known tracks to obtain a list of all possible plot-track pairs • One commonly used comparison method which results shortest possible comparison time is to organized the tracks such that they are compared with smallest possible no. of plots The Tracking Process - Updating
- 154. 154 • Depending on implementations, a central sector covering >1 track sectors, e.g. 2 track sectors and therefore 3 plot sectors, is defined for detecting plots that have evolved to non-adjacent sectors (fast moving targets or small sector size) • If there exists a central sector, an unsuccessful correlation of plots (from the 2 adjacent plots) to a track, comparison is made with plots in the central sector The Tracking Process - Updating
- 155. 155 • 1 simple way to resolve such problem is to generate a plot-track distance matrix, a plot is then associated to a track it lies within the gate, the distance between the correlated plot and the track is computed and stored in the matrix • After the comparison cycle, some common situations can occur – 1 plot is associated to 1 track – 1 plot is associated to several tracks – several plots are assigned to 1 track – no associated of plot to any track The Tracking Process - Updating
- 156. 156 • Consider a plot-track distance matrix, it is obvious that plot 3 is associated to track 3 (deleted from matrix), plot 1 is associated to track 1 (delete from matrix) The Tracking Process - Updating Track 1 Track 2 Track 3 Plot 1 1 4 15 Plot 2 3 3 13 Plot 3 12 10 3 Plot 4 5 3 10
- 157. 157 • Plot 2 and 4 can be associated to track 2, one simple way to resolve the problem is to assign plot 2 randomly (wrong assignment will be rectified after a few more scans) • The remaining plots are considered for new track initiation and remaining tracks can considered termination The Tracking Process - Updating Track 1 Track 2 Track 3 Plot 1 1 4 15 Plot 2 3 3 13 Plot 3 12 10 3 Plot 4 5 3 10
- 158. 158 • After association, the track information are stored in the target database; the measured position (if there is an associated plot) is updated, otherwise the predicted position is used • Predicted position is obtained by filtering (e.g. Kalman or ab filter) which filters and predicts target position The Tracking Process - Updating
- 159. 159 The Tracking Process - Updating Predicted position Track Updated track Out of search window Out of shape New search window New prediction • The plot-to-track correlation
- 160. 160 • The quality factor, status of the track, gate size and position is computed • The quality factor of a track depends on the track history (how good it was), it is used to compute the gate size for the next scan (smaller or larger) • The quality factor is computed as where K = +ve when there is a plot in the gate and K = -ve there is no plot in the gate The Tracking Process - Updating KQQ nn 1
- 161. 161 The Tracking Process - Updating
- 162. 162 • This process is performed once every scan for every track, an associated plot is known as a hit where a non-associated plot is a miss • A track is cancelled automatically when plot is absent for a predefined no. of scans consecutive or Q = 0 (no point tracking) • A track is also terminated manually when drop track function is invoked • This erases all data corresponding to the track in the target table, the lost target symbol is displayed for reference The Tracking Process - Termination
- 163. 163 • A miss The Tracking Process - Termination Predicted position Track This will count as a lack – no update found
- 164. 164 The End