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Radar 2009 a 15 parameter estimation and tracking part 1

The document discusses a lecture on parameter estimation and tracking in radar systems. It covers topics like observable estimation including range, angle, Doppler, and amplitude measurement accuracy. It also discusses single target tracking techniques such as amplitude monopulse, phase comparison monopulse, sequential lobing, and conical scanning. The outline indicates it will cover multiple target tracking and provide a summary. Diagrams are included to illustrate concepts like angular tracking error sources and Doppler estimation.

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IEEE New Hampshire Section Radar Systems Course 1 Parameter Estimation 1/1/2010 IEEE AES Society Radar Systems Engineering Lecture 15 Parameter Estimation And Tracking Part 1 Dr. Robert M. O’Donnell IEEE New Hampshire Section Guest Lecturer
Radar Systems Course 2 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Pulse Compression Receiver Clutter Rejection (Doppler Filtering) A / D Converter Block Diagram of Radar System Antenna Propagation Medium Target Radar Cross Section Transmitter General Purpose Computer Tracking Data Recording Parameter Estimation Waveform Generation Detection Power Amplifier T / R Switch Signal Processor Computer Thresholding User Displays and Radar Control Photo Image Courtesy of US Air Force
Radar Systems Course 3 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Tracking Radars MOTR MPQ-39 TRADEX BMEWS Courtesy of Lockheed Martin. Used with permission. Courtesy of US Air Force FPS-16 Courtesy of MIT Lincoln Laboratory, Used with Permission Courtesy of Raytheon, Used with Permission Courtesy of FAACourtesy of FAA FAA ASR
Radar Systems Course 4 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking • Multiple Target Tracking • Summary
Radar Systems Course 5 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Radar Parameter Estimation Radar Target • Location – Range – Azimuth Angle – Elevation Angle • Size – Amplitude (RCS) – Radial Extent – Cross Range Extent • Motion – Radial Velocity (Doppler) – Acceleration – Angular Motion about Center of Mass – Ballistic Coefficient Quantities in Blue Are Usually Measured Directly Measured Radar Observables
Radar Systems Course 6 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Accuracy, Precision and Resolution • Precision: – Repeatability of a measurement • Accuracy: – The degree of conformity of measurement to the true value – Bias Error : True value- Average measured value • Resolution: – Offset (angle or range) required for two targets to be recognized as separate targets Amplitude(dB) Angle (deg) Angle (deg) Amplitude(dB) Targets at 0° and 6° Targets at 0° and 3° Example Accuracy vs. Precision Low Accuracy Low Precision Low Accuracy High Precision High Accuracy High Precision -10 0 10 20 -10 0 10 20 0 0 -10 -20 -30-30 -20 -10
Radar Systems Course 7 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation – Range – Angle – Doppler – Amplitude of reflected echo from target • Single Target Tracking • Multiple Target Tracking • Summary
Radar Systems Course 8 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Observable Accuracy • Observable to be discussed – Range – Angle – Doppler Velocity • After bias errors are accounted for, noise is the key limiting factor in accurately measuring the above observables – The exception is angle measurement, where for low angle tracking multipath errors can predominate • The theoretical rms error of a measurement is of the form – Where is a constant between .5 and 1 Mδ M N/S Mk M =δ k
Radar Systems Course 9 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Limitations on Range Estimation • Estimation of the range of a target is based upon using A/D sampled measurements of the round trip time to and from the target • For time delay measurements , such as range, the value of the constant depends on the shape of the radar pulse’s spectrum and the pulse’s rise time. • For a rectangular pulse, whose width is – Which yields • For a train of pulses it becomes: 2 Tc R R = k N/S2 T T ≈δT N/S2 Tc R =δ Adapted from Barton and Ward Reference 6 ( )( ) DTPRFN/S2 Tc R =δ DT = Dwell Time
Radar Systems Course 10 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Theoretical vs. Practical Accuracy Limitations • General – Section 6.3 of Skolnik reference 1 derives the theoretical limitations for each of the pertinent observables Time, frequency, and angle • Range – S/N, pulse shape and width, effective bandwidth, number of pulses • Doppler Frequency – S/N, pulse shape, integration time • Angle – S/N, type of measurement technique, antenna illumination distribution, antenna size, frequency
Radar Systems Course 11 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angle Estimation Issues ProbabilityDensityFunction Angle of ArrivalBiased Estimators Unbiased Estimators Target Location LOW SNR HIGH SNR CALIBRATION ERRORS MULTIPATH ERRORS Courtesy of MIT Lincoln Laboratory, Used with Permission
Radar Systems Course 12 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Limitation on Angle Estimation Sources of Error Signal to Noise Ratio Monopulse vs. Conical Scan Servo Noise Amplitude Fluctuations RMSAngularTrackingError (RMS) Relative Radar Range Total Error Monopulse Receiver Noise (monopulse) Amplitude FluctuationsServo Noise Receiver Noise (conical scan) Total Error Conical Scan 0.3 0.001 0.03 0.01 0.03 0.1 1 3 10 30 100 300 1000 Glint N/S 7. DB3θ ≈δθ Adapted from Skolnik Reference 1
Radar Systems Course 13 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angular Accuracy with ASR Radar • Angular beam splitting with Track While Scan Radar – ~10 : 1 splitting measured To radar 1/16 nmi Target Detections From 4 CPI’s 1Beamwidth Accuracy of 100 tracks Azimuth Error (deg) Sample Tracker Output NumberofTracks 0.0 0.2 0.4 Average Error 0.14°10 nmi 20 nmi Track Used
Radar Systems Course 14 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Doppler Estimation Doppler Frequency -50 -40 -30 -20 -10 0 -50 -40 -30 -20 -10 0 Doppler Frequency FilterResponse[dB] fd = 2vr λ Doppler Frequency Radial Velocity Wavelength • Filter-bank spans entire radar system Doppler frequency band • Detections are isolated within a single Doppler filter • Use two closely spaced frequency filters offset from the center frequency of the Doppler filter containing the detection • Doppler estimation procedure is similar to angle estimation with angle and frequency interchanged Detect Estimate Courtesy of MIT Lincoln Laboratory, Used with Permission
Radar Systems Course 15 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Radar Cross Section Measurement Accuracy • Measurement of the radar cross section (RCS) of a target in a test environment was discussed in detail in the lecture on Radar Cross Section (Lecture10) • When one wants to measure the RCS of a target, the radar needs to be calibrated – How do A/D counts relate to RCS values? • This calibration process is usually accomplished by launching a balloon with a sphere (RCS independent of orientation) attached by a lengthy tether and measuring the amplitude in A/D counts and the range of the balloon
Radar Systems Course 16 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Radar Cross Section Measurement Accuracy • The calibration process (continued) – Measurement is performed in the far field – A radiosonde is usually balloon launched separately to measure the pressure, temperature, etc. (index of refraction of the atmosphere vs. height) so that propagation effects, such as, ducting, multipath, etc., may be taken into account properly and accurately • High power radars could use spherical satellites to perform the same function as the balloon borne sphere • RCS accuracy is usually limited by the ability to measure atmospheric (properties) losses as a function of the sphere’s range and elevation angle
Radar Systems Course 17 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary Courtesy of MIT Lincoln Laboratory. Used with permission TRADEX FPS-16 Courtesy of US Air Force
Radar Systems Course 18 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Single Target Tracking - General • Usually after a target is initially detected, the radar is asked to: – Continue to detect the target as it moves through the radar’s coverage – Associate the different detections with the specific target “All these detections are from the same target” Use range, angle, Doppler measurements – Use these detections to develop a continually more accurate estimate of the targets observables Position, velocity, etc – Predict where the target will be is the future • These are the functions of a “Tracker”
Radar Systems Course 19 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Basics of Continuous Angle Tracking • For radars with a dish antenna, the purpose of the tracking function is to keep the antenna beam axis aligned with a selected target. • Illustration at left – Two overlapping beams - target is to the right of antenna boresight • Illustration at right – Two overlapping beams - target is to the right of antenna boresight . Target is located at boresight position. Beam ABeam A Beam B Beam B Angle Aa Ba Aa Ba 0θ T0 θ=θTθ Angle Boresight Boresight Target DirectionTarget Direction BA aa < BA aa = Adapted from Skolnik Reference 1
Radar Systems Course 20 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
Radar Systems Course 21 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Amplitude Comparison Monopulse • Amplitude Comparison Monopulse Method: – Use pairs of slightly offset beams to determine the location of the target relative to the antenna boresight (error signal) – Use this information to re-steer the antenna (or beam) to keep the target very close to the antenna boresight • For dish antennas, two offset receive beams are generated by using two feeds slightly displaced in opposite directions from the focus of a parabolic reflector • The sum and difference of the two squinted beams are used to generate the error signal • Each channel (sum, azimuth difference, and elevation difference) requires a separate receiver
Radar Systems Course 22 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Monopulse Antenna Patterns and Error Signals θ θ θ Overlapping Antenna Patterns Difference Pattern Sum Pattern Error Signal vs. Angle Angle ErrorSignal )(cosSignalError ΔΣ φ−φ Σ Δ = Δ Σ Adapted from Skolnik Reference 1
Radar Systems Course 23 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Four Horn Monopulse Block Diagram A D C B Antenna Feed Sum Hybrid Junction A D C B Receiver Azimuth Difference T/R Device Transmitter Elevation Difference Sum Σ Σ Σ Δ Δ Σ Δ Front Elevation Difference Sum Azimuth Difference Adapted from Skolnik Reference 1
Radar Systems Course 24 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Two Dimensional- Four Horn Monopulse B D A C B D A C B+A – (C+D) B D A C A+B+C+D Sum beam Σ Elevation difference beam Δ EL Azimuth difference beam Δ AZ B D A C B+D – (A+C) Radar Antenna Feed Antenna Dish • Σ = Sum channel signal Δ = Difference channel signal φ = phase difference between Σ and Δ • Error signal e = Note that the lower feeds generate the upper beams | Δ | cos φ | Σ | A C B D
Radar Systems Course 25 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Monopulse Error Pattern Off-Axis Angle 0 0 1.0 1.0 -1.0 -1.0 0.5 0.5 - 0.5 -0.5 VoltagePattern Sum = Difference = Δ Σ )(cos ΔΣ φ−φ Σ Δ
Radar Systems Course 26 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Functional Diagram of Monopulse Radar Microwave Combining Network Duplexer Transmitter Antenna Drive Servos Coordinate Transformation Azimuth Difference Receiver Sum Receiver Elevation Difference Receiver Elevation Monopulse Processor Azimuth Monopulse Processor From Antenna Feed Horns D C B A Σ AZΔ )(cos)el&az(Error ΔΣ φ−φ Σ Δ = Antenna Mechanical Drive For Detection and Range Measurement ELΔ Azimuth Elevation Adapted from Sherman Reference 5
Radar Systems Course 27 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Microwave Combining Network (Four Horn Monopulse Feed) Hybrid Junction 1 Hybrid Junction 2 Hybrid Junction 4 Hybrid Junction 3φ φ B A C D C A D B Arrangement Of Horns 90° -90° 1 11 1 2 3 4 2 2 2 3 33 44 4 jB -jC 2/)BA( − 2/)BA(j + 2/)DC(j −− 2/)DC( + [ ])DB()CA(2/1 +−+ [ ])DC()BA(2/1 −−− Diagonal Difference (terminated, not used) Elevation Difference Azimuth Difference Sum [ ]DCBA2/1 +++ [ ])BA()DC(2/1 +−+ Adapted from Sherman Reference 5
Radar Systems Course 28 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Three Types of Hybrid Junctions 3 dB Directional CouplerPort D Port C Port B Port A Primary Waveguide Secondary Waveguide Waves Add Waves Cancel 4/gλ Magic - T 4/3 gλ 4 gλ 4 gλ 4 gλ Port D Port A Port C Port B a b Hybrid Ring Junction or “Rat-Race” Courtesy ofCourtesy of CobhamCobham Sensor Systems.Sensor Systems. Used with permission.Used with permission.
Radar Systems Course 29 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Hybrid Junctions for Monopulse Radars • A signal input at port A divides equally in amplitude and phase between ports C and D, but does not appear at port B – Port B cannot support that propagation mode • A signal input to port B divides equally but with opposite phases between ports C and D – Does not appear at port A • If inputs are applied simultaneously to ports A and B, their sum will appear at port C and the difference at the D Photograph of C - Band Magic - T (Ridged waveguide) A D C B Δ Σ Magic - T Courtesy ofCourtesy of CobhamCobham Sensor Systems.Sensor Systems. Used with permission.Used with permission.
Radar Systems Course 30 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Hybrid Junctions Used in Monopulse Radar Hybrid Ring Junction or “Rat-Race” • A signal input at port A reaches output port D by two separate paths, which have the same path length ( 3λ/4) – The two paths reinforce at port D • An input signal at port B reaches output port D through paths differing by one wavelength ( 5λ/4 and λ/4) – The two paths reinforce at port D • Paths from A to D and B to D differ by 1/2 wavelength – Signal at port A - signal at port B will appear at port D • If signals of the same phase are entered at A and , the outputs C and D are the sum (Σ) and difference (Δ). 4/3 gλ 4 gλ 4 gλ 4 gλ Port D Port A Port C Port B a b
Radar Systems Course 31 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society • This coupler is made by aligning two rectangular waveguides with their walls touching • Microwave energy from one of the waveguides is coupled to the other by means of appropriate holes or slots between the two waveguides – Because of the quarter wave spacing between the two slots, this configuration is frequency sensitive – A 90 degree phase shift has to be inserted in either port A or B in order to provide the sum and difference at ports C and D Hybrid Junctions Used in Monopulse Radar 3 dB Directional CouplerPort D Port C Port B Port A Primary Waveguide Secondary Waveguide Waves Add Waves Cancel 4/gλ
Radar Systems Course 32 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Monopulse Processor )(cos ΔΣ φ−φ Σ Δ Computer 2 QQII Re Σ ΣΔ+ΣΔ =⎟ ⎠ ⎞ ⎜ ⎝ ⎛ Σ Δ 2 Q 2 I Σ+Σ=Σ 2 Q 2 I Δ+Δ=Δ 2 QIIQ Im Σ ΣΔ−ΣΔ =⎟ ⎠ ⎞ ⎜ ⎝ ⎛ Σ Δ Σ A/D A/D A/D A/D 90° Phase Shift Reference Oscillator Δ QΣ IΣ IΔ QΔ Adapted from Sherman Reference 5
Radar Systems Course 33 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society S Band Monopulse Feed with X Band Center Feed From S and X Band Transmitters Four Horn Monopulse S band Feed (X band Feed at center) Output Front View of Output Side View Courtesy of MIT Lincoln Laboratory, Used with Permission
Radar Systems Course 34 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Twelve Horn Monopulse Feed Photograph of 12 Horn Monopulse Feed Courtesy of MIT Lincoln Laboratory, Used with Permission
Radar Systems Course 35 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Glint (Angle Noise) • Glint, or angle noise, is a fluctuation or error in the angle measurement caused by the radar’s energy reflecting from a complex target with multiple scattering centers – It causes a distortion of the echo wavefront – The result of having a non-uniform wavefront from a complex target, when the radar was designed to process a planar echo wavefront, is an error in the measurement of the angle of arrival – The measured angle of arrival can often cause the boresight of the tracking antenna to point outside the angular extent of the target, which can cause the radar to break track • Glint can be a major source of error when making angle measurements – Short range where angular extent of target is large • Problem for all tracking radars with closed loop angle tracking – Monopulse, conical scan, sequential lobing
Radar Systems Course 36 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Low Angle Tracking • The target is illuminated via two paths (direct and reflection) • Error in measured elevation angle occurs because of glint – At low grazing angles, reflection coefficient close to -1 • Tracking of targets at low elevation angles can produce significant errors in the elevation angle and can cause loss of track • The surface reflected signal is sometimes called the multi-path signal and the glint error due to this geometry a multi-path error Radar Direct path Multipath Ray Target
Radar Systems Course 37 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Measured Low Angle Tracking Error Track Time (Minutes) Aircraft Tracked by S-Band Phased Array radar (FPS-16 provided “Truth) ElevationError(Degrees) 0 2 1 -1 -2 Azimuth (deg) 32.5 30.7 30.4 30.3 30.3 30.2 Elevation (deg) 3.0 2.4 2.0 1.7 1.4 1.3 Range (km) 19.9 24.3 28.9 33.5 38.1 42.7 Adapted from Skolnik Reference 1
Radar Systems Course 38 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
Radar Systems Course 39 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Phase Comparison Monopulse Two antennas radiating identical beams in the same direction Geometry of the signals at the two antennas when received from a target at an angle θ The phase difference of the signals received from the two antennas is : θ λ π=φΔ sin d 2 d d d θ Also known as “interferometer radar”
Radar Systems Course 40 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society • Amplitude Comparison Monopulse – Common phase center, beams squinted away from axis – Target produces signal with same phase but different amplitudes (On axis amplitudes equal) • Phase Comparison Monopulse – Beams parallel and identical – Lateral displacement of phase center much greater than – Target produces signal with same amplitude but different phase (On axis phases equal) – Grating lobes and high sidelobes a problem Comparison of Monopulse Antenna Beams Axis Axis λ
Radar Systems Course 41 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angle Estimation with Antenna Arrays W avefronts Antenna Array Received Phasefront θ Direction of Propagation • Received signal varies in phase across array • Phase rate of change related to direction of propagation • Estimating phase rate of change indicates direction of propagation – Angle-Of-Arrival (AOA) – Direction-Of Arrival (DOA) Courtesy of MIT Lincoln Laboratory, Used with Permission
Radar Systems Course 42 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
Radar Systems Course 43 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Sequential Lobing Angle Measurement • The Sequential Lobing angle tracking technique time shares a single antenna beam to obtain the angle measurement in a sequential manner V1 = voltage from upper beam (lobe) V2 = voltage from lower beam (lobe) If V1-V2 > 0 Antenna pointing to high If V1-V2 < 0 Antenna pointing to low If V1-V2 = 0 Antenna pointed at target Beam 1 Beam 2 Antenna pointed at target Adapted from Sherman Reference 5
Radar Systems Course 44 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Sequential Lobing Angle Measurement • The differences in echo signals between the two switched beams is a measure of the angular displacement of the target from the switching axis – The beam with the larger signal is closer to the target – A control loop is used to redirect the beam track locations to equalize the beam response – When the echo signals in the two beam positions are equal, the target is on axis Antenna Patterns Position 1 Time Position 2 Center of Beam 2 Center of Beam 1 Switching Axis Target Position
Radar Systems Course 45 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
Radar Systems Course 46 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Conical Scan Tracking Concept • The angle between the axis of rotation and the axis of the antenna beam is the squint angle • Because of the rotation of the squinted beam and the targets offset from the rotation axis, the amplitude of the echo signal will be modulated at a frequency equal to the beam rotation Typical Conical Scan Pattern (8 Beam Positions per Scan) Scan Pattern Beam Rotation Target Axis Rotation Axis Beam Axis Antenna Pattern Squint Angle
Radar Systems Course 47 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Conical Scan Pulse Trains • The amplitude of the modulation is proportional to the angular distance between the target direction and the rotation axis – Beam displacement • The phase of the modulation relative to the beam scanning position contains the direction information – Angle error Received Pulse Train with Conical-Scan Modulation ReceivedPulseAmplitude Time Envelope of Received Pulses Received Pulses
Radar Systems Course 48 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Block Diagram of Conical Scan Radar Range Gate Duplexer Receiver Transmitter Elevation Servo Amplifier Elevation Servo Motor Azimuth Servo Amplifier Elevation Angle Error Detector Azimith Angle Error Detector Azimuth Servo Motor Reference Generator To Rotary Joint On Antenna In Pedestal tf2sin sπ tf2cos sπ Error Signal Scan Motor
Radar Systems Course 49 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Beam-Splitting At typical detection threshold levels (~13 dB) the resolution cell can be approximately split by a factor of ten; i.e. 10:1 antenna beam splitting -10 0 10 20 30 0 0.2 0.4 0.6 0.8 1 Conical Scan , 1 pulse Monopulse, 1 pulse Conical Scan, 4 pulses Monopulse, 4 pulses Signal-to-noise ratio [dB] Error/Beamwidth SNR = 13 dB 10:1 Beam splitting Legend Courtesy of MIT Lincoln Laboratory, Used with Permission
Radar Systems Course 50 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angle Estimation with Scanning Radar (Multiple Pulse Angle Estimation) Scan Angle Target Power Antenna Pattern (e.g. azimuth) Scan Angle Target Power Antenna Pattern Antenna Pattern Scan Angle Declared Target Power Scanned Output Power Detection Threshold Detection Threshold Courtesy US Dept of Commerce Airport Surveillance Radar Courtesy of MIT Lincoln Laboratory, Used with Permission
Radar Systems Course 51 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angle Estimation with Scanning Radar (Multiple Pulse Angle Estimation) Scan Angle Target Power Antenna Pattern Scan Angle Target Power Antenna Pattern Antenna Pattern Scan Angle Declared Target Power Scanned Output Power Detection Threshold • For a “track-while scan” radar, the target angle is measured by: – Fitting the return angle data from different angles to the known antenna pattern, or – Using the highest amplitude target return as the measured target angle location Detection Threshold Courtesy of MIT Lincoln Laboratory, Used with Permission
Radar Systems Course 52 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angle Estimation with Array Antennas • Phased array radars are well suited for monopulse tracking – Amplitude Comparison Monopulse Radiating elements can be combined in 3 ways Sum, azimuth difference, and elevation difference patterns – Phase Comparison Monopulse Use top and bottom half of array for elevation Use right and left half of array for azimuth • Lens arrays (e.g. MOTR) would use amplitude monopulse – Four-port feed horn would be same as for dish reflector MOTR BMEWS Courtesy of MIT Lincoln Laboratory, Used with Permission
Radar Systems Course 53 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
Radar Systems Course 54 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Split Gate Range Tracking Early Gate Signal Difference Signal between Early and Late Range Gates Late Gate Early Gate Echo Pulse Late Gate Signal • Two gates are generated; one is an early gate, the other is a late gate. • In this example, the portion of the signal in the early gate is less than that of the late gate. • The signals in the two gates are integrated and subtracted to produce the difference error signal. • The sign of the difference indicates the direction the two gates have to be moved in order to have the pair straddle the echo pulse • The amplitude of the difference determines how far the pair of gates are from the centroid.
Radar Systems Course 55 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Multi Target Tracking in Range, Angle, and Doppler • Single target angle trackers (Dish radars) can be configured to track other targets in the radar beam – Useful for radars with moderate to wide beamwidths – Favorable geometry helpful • TRADEX and several other radars have multi-target trackers – Primary target is kept on boresight with standard monopulse angle tracker – Up to 10 other targets, in radar beamwidth, are tracked in range • Some other radars track in Doppler and in range along with tracking in angle
Radar Systems Course 56 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
Radar Systems Course 57 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Antenna Servo Systems • The automatic tracking of a target in angle employs a servo system that utilizes the angle error signals to maintain the pointing of the antenna in the direction of the target • The servo system introduces lag in the tracking that results in error – The lag error depends on the target trajectory Straight line, gradual turn, rapid maneuver • Type II Servo System often used in tracking radar – No steady state error when target velocity constant – Known as “zero velocity error system” • The effect of velocity and acceleration on a servo system can be described by the frequency response of the tracking loop
Radar Systems Course 58 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Servo Bandwidth • The tracking bandwidth of a servo system is that of a low pass filter • The bandwidth should be narrow to: Minimize the effects of noise,or jitter, Reject unwanted signal components Conical scan frequency or jet engine modulation Provide a smoothed output of the desired measured parameters • The bandwidth should be wide to: Follow rapid changes in the target trajectory or in the vehicle carrying the radar • The choice of servo bandwidth is usually a compromise – Sensitivity vs. tracking of maneuvering target • Tracking bandwidth may be made variable or adaptive Far range - angle rates low, low S/N (narrow bandwidth) Short range - angle rates large (wide bandwidth) Shorter ranges - Glint can be an issue (narrow bandwidth)
Radar Systems Course 59 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Bounds on Servo Resonant Frequency • The tracking bandwidth of a mechanical tracker should be small compared to the lowest natural frequency of the antenna and its structural foundation – This prevents the antenna from oscillating at its resonant frequency ServoResonantFrequency(Hz) Antenna Diameter (ft) 1 3 10 30 100 300 10 1 30 3 100 APG-66 SCR-584 FPS-16 FPQ-10 FPQ-6 FPS-49 Goldstone Haystack
Radar Systems Course 60 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Summary – Part 1 • A detailed description of the different radar observables and their estimation was presented – Observables - Range, angle, and Doppler velocity – Radar cross section issues were presented in a previous lecture – Resolution, precision and accuracy were discussed • The different techniques for single target angle tracking were discussed in detail, as well as their implementation – Amplitude monopulse – Phase comparison monopulse – Sequential lobing – Conical scanning • Range tracking techniques, as well as other related subjects were presented
Radar Systems Course 61 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Homework Problems • From Skolnik, Reference 1 – Problems 4.1, 4.3, 4.5, 4.9, 4.11, and 4.15
Radar Systems Course 62 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society References 1. Skolnik, M., Introduction to Radar Systems, McGraw-Hill, New York, 3rd Ed., 2001 2. Barton, D. K., Modern Radar System Analysis, Norwood, Mass., Artech House, 1988 3. Skolnik, M., Editor in Chief, Radar Handbook, New York, McGraw-Hill, 3rd Ed., 2008 4. Skolnik, M., Editor in Chief, Radar Handbook, New York, McGraw-Hill, 2nd Ed., 1990 5. Sherman, S. M., Monopulse Principles and Techniques, Norwood, Mass., Artech House, 1984 6. Barton, D. K. and Ward, H. R, Handbook of Radar Measurements, Norwood, Mass., Artech House, 1984
Radar Systems Course 63 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Acknowledgements • Dr Katherine A. Rink • Dr Eli Brookner, Raytheon Co.
Radar Systems Course 64 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Part 2 • Introduction • Observable Estimation • Single Target Tracking • Multiple Target Tracking • Summary

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Radar 2009 a 15 parameter estimation and tracking part 1

  • 1.
    IEEE New HampshireSection Radar Systems Course 1 Parameter Estimation 1/1/2010 IEEE AES Society Radar Systems Engineering Lecture 15 Parameter Estimation And Tracking Part 1 Dr. Robert M. O’Donnell IEEE New Hampshire Section Guest Lecturer
  • 2.
    Radar Systems Course2 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Pulse Compression Receiver Clutter Rejection (Doppler Filtering) A / D Converter Block Diagram of Radar System Antenna Propagation Medium Target Radar Cross Section Transmitter General Purpose Computer Tracking Data Recording Parameter Estimation Waveform Generation Detection Power Amplifier T / R Switch Signal Processor Computer Thresholding User Displays and Radar Control Photo Image Courtesy of US Air Force
  • 3.
    Radar Systems Course3 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Tracking Radars MOTR MPQ-39 TRADEX BMEWS Courtesy of Lockheed Martin. Used with permission. Courtesy of US Air Force FPS-16 Courtesy of MIT Lincoln Laboratory, Used with Permission Courtesy of Raytheon, Used with Permission Courtesy of FAACourtesy of FAA FAA ASR
  • 4.
    Radar Systems Course4 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking • Multiple Target Tracking • Summary
  • 5.
    Radar Systems Course5 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Radar Parameter Estimation Radar Target • Location – Range – Azimuth Angle – Elevation Angle • Size – Amplitude (RCS) – Radial Extent – Cross Range Extent • Motion – Radial Velocity (Doppler) – Acceleration – Angular Motion about Center of Mass – Ballistic Coefficient Quantities in Blue Are Usually Measured Directly Measured Radar Observables
  • 6.
    Radar Systems Course6 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Accuracy, Precision and Resolution • Precision: – Repeatability of a measurement • Accuracy: – The degree of conformity of measurement to the true value – Bias Error : True value- Average measured value • Resolution: – Offset (angle or range) required for two targets to be recognized as separate targets Amplitude(dB) Angle (deg) Angle (deg) Amplitude(dB) Targets at 0° and 6° Targets at 0° and 3° Example Accuracy vs. Precision Low Accuracy Low Precision Low Accuracy High Precision High Accuracy High Precision -10 0 10 20 -10 0 10 20 0 0 -10 -20 -30-30 -20 -10
  • 7.
    Radar Systems Course7 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation – Range – Angle – Doppler – Amplitude of reflected echo from target • Single Target Tracking • Multiple Target Tracking • Summary
  • 8.
    Radar Systems Course8 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Observable Accuracy • Observable to be discussed – Range – Angle – Doppler Velocity • After bias errors are accounted for, noise is the key limiting factor in accurately measuring the above observables – The exception is angle measurement, where for low angle tracking multipath errors can predominate • The theoretical rms error of a measurement is of the form – Where is a constant between .5 and 1 Mδ M N/S Mk M =δ k
  • 9.
    Radar Systems Course9 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Limitations on Range Estimation • Estimation of the range of a target is based upon using A/D sampled measurements of the round trip time to and from the target • For time delay measurements , such as range, the value of the constant depends on the shape of the radar pulse’s spectrum and the pulse’s rise time. • For a rectangular pulse, whose width is – Which yields • For a train of pulses it becomes: 2 Tc R R = k N/S2 T T ≈δT N/S2 Tc R =δ Adapted from Barton and Ward Reference 6 ( )( ) DTPRFN/S2 Tc R =δ DT = Dwell Time
  • 10.
    Radar Systems Course10 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Theoretical vs. Practical Accuracy Limitations • General – Section 6.3 of Skolnik reference 1 derives the theoretical limitations for each of the pertinent observables Time, frequency, and angle • Range – S/N, pulse shape and width, effective bandwidth, number of pulses • Doppler Frequency – S/N, pulse shape, integration time • Angle – S/N, type of measurement technique, antenna illumination distribution, antenna size, frequency
  • 11.
    Radar Systems Course11 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angle Estimation Issues ProbabilityDensityFunction Angle of ArrivalBiased Estimators Unbiased Estimators Target Location LOW SNR HIGH SNR CALIBRATION ERRORS MULTIPATH ERRORS Courtesy of MIT Lincoln Laboratory, Used with Permission
  • 12.
    Radar Systems Course12 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Limitation on Angle Estimation Sources of Error Signal to Noise Ratio Monopulse vs. Conical Scan Servo Noise Amplitude Fluctuations RMSAngularTrackingError (RMS) Relative Radar Range Total Error Monopulse Receiver Noise (monopulse) Amplitude FluctuationsServo Noise Receiver Noise (conical scan) Total Error Conical Scan 0.3 0.001 0.03 0.01 0.03 0.1 1 3 10 30 100 300 1000 Glint N/S 7. DB3θ ≈δθ Adapted from Skolnik Reference 1
  • 13.
    Radar Systems Course13 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angular Accuracy with ASR Radar • Angular beam splitting with Track While Scan Radar – ~10 : 1 splitting measured To radar 1/16 nmi Target Detections From 4 CPI’s 1Beamwidth Accuracy of 100 tracks Azimuth Error (deg) Sample Tracker Output NumberofTracks 0.0 0.2 0.4 Average Error 0.14°10 nmi 20 nmi Track Used
  • 14.
    Radar Systems Course14 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Doppler Estimation Doppler Frequency -50 -40 -30 -20 -10 0 -50 -40 -30 -20 -10 0 Doppler Frequency FilterResponse[dB] fd = 2vr λ Doppler Frequency Radial Velocity Wavelength • Filter-bank spans entire radar system Doppler frequency band • Detections are isolated within a single Doppler filter • Use two closely spaced frequency filters offset from the center frequency of the Doppler filter containing the detection • Doppler estimation procedure is similar to angle estimation with angle and frequency interchanged Detect Estimate Courtesy of MIT Lincoln Laboratory, Used with Permission
  • 15.
    Radar Systems Course15 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Radar Cross Section Measurement Accuracy • Measurement of the radar cross section (RCS) of a target in a test environment was discussed in detail in the lecture on Radar Cross Section (Lecture10) • When one wants to measure the RCS of a target, the radar needs to be calibrated – How do A/D counts relate to RCS values? • This calibration process is usually accomplished by launching a balloon with a sphere (RCS independent of orientation) attached by a lengthy tether and measuring the amplitude in A/D counts and the range of the balloon
  • 16.
    Radar Systems Course16 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Radar Cross Section Measurement Accuracy • The calibration process (continued) – Measurement is performed in the far field – A radiosonde is usually balloon launched separately to measure the pressure, temperature, etc. (index of refraction of the atmosphere vs. height) so that propagation effects, such as, ducting, multipath, etc., may be taken into account properly and accurately • High power radars could use spherical satellites to perform the same function as the balloon borne sphere • RCS accuracy is usually limited by the ability to measure atmospheric (properties) losses as a function of the sphere’s range and elevation angle
  • 17.
    Radar Systems Course17 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary Courtesy of MIT Lincoln Laboratory. Used with permission TRADEX FPS-16 Courtesy of US Air Force
  • 18.
    Radar Systems Course18 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Single Target Tracking - General • Usually after a target is initially detected, the radar is asked to: – Continue to detect the target as it moves through the radar’s coverage – Associate the different detections with the specific target “All these detections are from the same target” Use range, angle, Doppler measurements – Use these detections to develop a continually more accurate estimate of the targets observables Position, velocity, etc – Predict where the target will be is the future • These are the functions of a “Tracker”
  • 19.
    Radar Systems Course19 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Basics of Continuous Angle Tracking • For radars with a dish antenna, the purpose of the tracking function is to keep the antenna beam axis aligned with a selected target. • Illustration at left – Two overlapping beams - target is to the right of antenna boresight • Illustration at right – Two overlapping beams - target is to the right of antenna boresight . Target is located at boresight position. Beam ABeam A Beam B Beam B Angle Aa Ba Aa Ba 0θ T0 θ=θTθ Angle Boresight Boresight Target DirectionTarget Direction BA aa < BA aa = Adapted from Skolnik Reference 1
  • 20.
    Radar Systems Course20 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
  • 21.
    Radar Systems Course21 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Amplitude Comparison Monopulse • Amplitude Comparison Monopulse Method: – Use pairs of slightly offset beams to determine the location of the target relative to the antenna boresight (error signal) – Use this information to re-steer the antenna (or beam) to keep the target very close to the antenna boresight • For dish antennas, two offset receive beams are generated by using two feeds slightly displaced in opposite directions from the focus of a parabolic reflector • The sum and difference of the two squinted beams are used to generate the error signal • Each channel (sum, azimuth difference, and elevation difference) requires a separate receiver
  • 22.
    Radar Systems Course22 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Monopulse Antenna Patterns and Error Signals θ θ θ Overlapping Antenna Patterns Difference Pattern Sum Pattern Error Signal vs. Angle Angle ErrorSignal )(cosSignalError ΔΣ φ−φ Σ Δ = Δ Σ Adapted from Skolnik Reference 1
  • 23.
    Radar Systems Course23 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Four Horn Monopulse Block Diagram A D C B Antenna Feed Sum Hybrid Junction A D C B Receiver Azimuth Difference T/R Device Transmitter Elevation Difference Sum Σ Σ Σ Δ Δ Σ Δ Front Elevation Difference Sum Azimuth Difference Adapted from Skolnik Reference 1
  • 24.
    Radar Systems Course24 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Two Dimensional- Four Horn Monopulse B D A C B D A C B+A – (C+D) B D A C A+B+C+D Sum beam Σ Elevation difference beam Δ EL Azimuth difference beam Δ AZ B D A C B+D – (A+C) Radar Antenna Feed Antenna Dish • Σ = Sum channel signal Δ = Difference channel signal φ = phase difference between Σ and Δ • Error signal e = Note that the lower feeds generate the upper beams | Δ | cos φ | Σ | A C B D
  • 25.
    Radar Systems Course25 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Monopulse Error Pattern Off-Axis Angle 0 0 1.0 1.0 -1.0 -1.0 0.5 0.5 - 0.5 -0.5 VoltagePattern Sum = Difference = Δ Σ )(cos ΔΣ φ−φ Σ Δ
  • 26.
    Radar Systems Course26 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Functional Diagram of Monopulse Radar Microwave Combining Network Duplexer Transmitter Antenna Drive Servos Coordinate Transformation Azimuth Difference Receiver Sum Receiver Elevation Difference Receiver Elevation Monopulse Processor Azimuth Monopulse Processor From Antenna Feed Horns D C B A Σ AZΔ )(cos)el&az(Error ΔΣ φ−φ Σ Δ = Antenna Mechanical Drive For Detection and Range Measurement ELΔ Azimuth Elevation Adapted from Sherman Reference 5
  • 27.
    Radar Systems Course27 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Microwave Combining Network (Four Horn Monopulse Feed) Hybrid Junction 1 Hybrid Junction 2 Hybrid Junction 4 Hybrid Junction 3φ φ B A C D C A D B Arrangement Of Horns 90° -90° 1 11 1 2 3 4 2 2 2 3 33 44 4 jB -jC 2/)BA( − 2/)BA(j + 2/)DC(j −− 2/)DC( + [ ])DB()CA(2/1 +−+ [ ])DC()BA(2/1 −−− Diagonal Difference (terminated, not used) Elevation Difference Azimuth Difference Sum [ ]DCBA2/1 +++ [ ])BA()DC(2/1 +−+ Adapted from Sherman Reference 5
  • 28.
    Radar Systems Course28 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Three Types of Hybrid Junctions 3 dB Directional CouplerPort D Port C Port B Port A Primary Waveguide Secondary Waveguide Waves Add Waves Cancel 4/gλ Magic - T 4/3 gλ 4 gλ 4 gλ 4 gλ Port D Port A Port C Port B a b Hybrid Ring Junction or “Rat-Race” Courtesy ofCourtesy of CobhamCobham Sensor Systems.Sensor Systems. Used with permission.Used with permission.
  • 29.
    Radar Systems Course29 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Hybrid Junctions for Monopulse Radars • A signal input at port A divides equally in amplitude and phase between ports C and D, but does not appear at port B – Port B cannot support that propagation mode • A signal input to port B divides equally but with opposite phases between ports C and D – Does not appear at port A • If inputs are applied simultaneously to ports A and B, their sum will appear at port C and the difference at the D Photograph of C - Band Magic - T (Ridged waveguide) A D C B Δ Σ Magic - T Courtesy ofCourtesy of CobhamCobham Sensor Systems.Sensor Systems. Used with permission.Used with permission.
  • 30.
    Radar Systems Course30 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Hybrid Junctions Used in Monopulse Radar Hybrid Ring Junction or “Rat-Race” • A signal input at port A reaches output port D by two separate paths, which have the same path length ( 3λ/4) – The two paths reinforce at port D • An input signal at port B reaches output port D through paths differing by one wavelength ( 5λ/4 and λ/4) – The two paths reinforce at port D • Paths from A to D and B to D differ by 1/2 wavelength – Signal at port A - signal at port B will appear at port D • If signals of the same phase are entered at A and , the outputs C and D are the sum (Σ) and difference (Δ). 4/3 gλ 4 gλ 4 gλ 4 gλ Port D Port A Port C Port B a b
  • 31.
    Radar Systems Course31 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society • This coupler is made by aligning two rectangular waveguides with their walls touching • Microwave energy from one of the waveguides is coupled to the other by means of appropriate holes or slots between the two waveguides – Because of the quarter wave spacing between the two slots, this configuration is frequency sensitive – A 90 degree phase shift has to be inserted in either port A or B in order to provide the sum and difference at ports C and D Hybrid Junctions Used in Monopulse Radar 3 dB Directional CouplerPort D Port C Port B Port A Primary Waveguide Secondary Waveguide Waves Add Waves Cancel 4/gλ
  • 32.
    Radar Systems Course32 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Monopulse Processor )(cos ΔΣ φ−φ Σ Δ Computer 2 QQII Re Σ ΣΔ+ΣΔ =⎟ ⎠ ⎞ ⎜ ⎝ ⎛ Σ Δ 2 Q 2 I Σ+Σ=Σ 2 Q 2 I Δ+Δ=Δ 2 QIIQ Im Σ ΣΔ−ΣΔ =⎟ ⎠ ⎞ ⎜ ⎝ ⎛ Σ Δ Σ A/D A/D A/D A/D 90° Phase Shift Reference Oscillator Δ QΣ IΣ IΔ QΔ Adapted from Sherman Reference 5
  • 33.
    Radar Systems Course33 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society S Band Monopulse Feed with X Band Center Feed From S and X Band Transmitters Four Horn Monopulse S band Feed (X band Feed at center) Output Front View of Output Side View Courtesy of MIT Lincoln Laboratory, Used with Permission
  • 34.
    Radar Systems Course34 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Twelve Horn Monopulse Feed Photograph of 12 Horn Monopulse Feed Courtesy of MIT Lincoln Laboratory, Used with Permission
  • 35.
    Radar Systems Course35 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Glint (Angle Noise) • Glint, or angle noise, is a fluctuation or error in the angle measurement caused by the radar’s energy reflecting from a complex target with multiple scattering centers – It causes a distortion of the echo wavefront – The result of having a non-uniform wavefront from a complex target, when the radar was designed to process a planar echo wavefront, is an error in the measurement of the angle of arrival – The measured angle of arrival can often cause the boresight of the tracking antenna to point outside the angular extent of the target, which can cause the radar to break track • Glint can be a major source of error when making angle measurements – Short range where angular extent of target is large • Problem for all tracking radars with closed loop angle tracking – Monopulse, conical scan, sequential lobing
  • 36.
    Radar Systems Course36 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Low Angle Tracking • The target is illuminated via two paths (direct and reflection) • Error in measured elevation angle occurs because of glint – At low grazing angles, reflection coefficient close to -1 • Tracking of targets at low elevation angles can produce significant errors in the elevation angle and can cause loss of track • The surface reflected signal is sometimes called the multi-path signal and the glint error due to this geometry a multi-path error Radar Direct path Multipath Ray Target
  • 37.
    Radar Systems Course37 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Measured Low Angle Tracking Error Track Time (Minutes) Aircraft Tracked by S-Band Phased Array radar (FPS-16 provided “Truth) ElevationError(Degrees) 0 2 1 -1 -2 Azimuth (deg) 32.5 30.7 30.4 30.3 30.3 30.2 Elevation (deg) 3.0 2.4 2.0 1.7 1.4 1.3 Range (km) 19.9 24.3 28.9 33.5 38.1 42.7 Adapted from Skolnik Reference 1
  • 38.
    Radar Systems Course38 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
  • 39.
    Radar Systems Course39 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Phase Comparison Monopulse Two antennas radiating identical beams in the same direction Geometry of the signals at the two antennas when received from a target at an angle θ The phase difference of the signals received from the two antennas is : θ λ π=φΔ sin d 2 d d d θ Also known as “interferometer radar”
  • 40.
    Radar Systems Course40 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society • Amplitude Comparison Monopulse – Common phase center, beams squinted away from axis – Target produces signal with same phase but different amplitudes (On axis amplitudes equal) • Phase Comparison Monopulse – Beams parallel and identical – Lateral displacement of phase center much greater than – Target produces signal with same amplitude but different phase (On axis phases equal) – Grating lobes and high sidelobes a problem Comparison of Monopulse Antenna Beams Axis Axis λ
  • 41.
    Radar Systems Course41 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angle Estimation with Antenna Arrays W avefronts Antenna Array Received Phasefront θ Direction of Propagation • Received signal varies in phase across array • Phase rate of change related to direction of propagation • Estimating phase rate of change indicates direction of propagation – Angle-Of-Arrival (AOA) – Direction-Of Arrival (DOA) Courtesy of MIT Lincoln Laboratory, Used with Permission
  • 42.
    Radar Systems Course42 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
  • 43.
    Radar Systems Course43 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Sequential Lobing Angle Measurement • The Sequential Lobing angle tracking technique time shares a single antenna beam to obtain the angle measurement in a sequential manner V1 = voltage from upper beam (lobe) V2 = voltage from lower beam (lobe) If V1-V2 > 0 Antenna pointing to high If V1-V2 < 0 Antenna pointing to low If V1-V2 = 0 Antenna pointed at target Beam 1 Beam 2 Antenna pointed at target Adapted from Sherman Reference 5
  • 44.
    Radar Systems Course44 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Sequential Lobing Angle Measurement • The differences in echo signals between the two switched beams is a measure of the angular displacement of the target from the switching axis – The beam with the larger signal is closer to the target – A control loop is used to redirect the beam track locations to equalize the beam response – When the echo signals in the two beam positions are equal, the target is on axis Antenna Patterns Position 1 Time Position 2 Center of Beam 2 Center of Beam 1 Switching Axis Target Position
  • 45.
    Radar Systems Course45 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
  • 46.
    Radar Systems Course46 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Conical Scan Tracking Concept • The angle between the axis of rotation and the axis of the antenna beam is the squint angle • Because of the rotation of the squinted beam and the targets offset from the rotation axis, the amplitude of the echo signal will be modulated at a frequency equal to the beam rotation Typical Conical Scan Pattern (8 Beam Positions per Scan) Scan Pattern Beam Rotation Target Axis Rotation Axis Beam Axis Antenna Pattern Squint Angle
  • 47.
    Radar Systems Course47 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Conical Scan Pulse Trains • The amplitude of the modulation is proportional to the angular distance between the target direction and the rotation axis – Beam displacement • The phase of the modulation relative to the beam scanning position contains the direction information – Angle error Received Pulse Train with Conical-Scan Modulation ReceivedPulseAmplitude Time Envelope of Received Pulses Received Pulses
  • 48.
    Radar Systems Course48 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Block Diagram of Conical Scan Radar Range Gate Duplexer Receiver Transmitter Elevation Servo Amplifier Elevation Servo Motor Azimuth Servo Amplifier Elevation Angle Error Detector Azimith Angle Error Detector Azimuth Servo Motor Reference Generator To Rotary Joint On Antenna In Pedestal tf2sin sπ tf2cos sπ Error Signal Scan Motor
  • 49.
    Radar Systems Course49 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Beam-Splitting At typical detection threshold levels (~13 dB) the resolution cell can be approximately split by a factor of ten; i.e. 10:1 antenna beam splitting -10 0 10 20 30 0 0.2 0.4 0.6 0.8 1 Conical Scan , 1 pulse Monopulse, 1 pulse Conical Scan, 4 pulses Monopulse, 4 pulses Signal-to-noise ratio [dB] Error/Beamwidth SNR = 13 dB 10:1 Beam splitting Legend Courtesy of MIT Lincoln Laboratory, Used with Permission
  • 50.
    Radar Systems Course50 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angle Estimation with Scanning Radar (Multiple Pulse Angle Estimation) Scan Angle Target Power Antenna Pattern (e.g. azimuth) Scan Angle Target Power Antenna Pattern Antenna Pattern Scan Angle Declared Target Power Scanned Output Power Detection Threshold Detection Threshold Courtesy US Dept of Commerce Airport Surveillance Radar Courtesy of MIT Lincoln Laboratory, Used with Permission
  • 51.
    Radar Systems Course51 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angle Estimation with Scanning Radar (Multiple Pulse Angle Estimation) Scan Angle Target Power Antenna Pattern Scan Angle Target Power Antenna Pattern Antenna Pattern Scan Angle Declared Target Power Scanned Output Power Detection Threshold • For a “track-while scan” radar, the target angle is measured by: – Fitting the return angle data from different angles to the known antenna pattern, or – Using the highest amplitude target return as the measured target angle location Detection Threshold Courtesy of MIT Lincoln Laboratory, Used with Permission
  • 52.
    Radar Systems Course52 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Angle Estimation with Array Antennas • Phased array radars are well suited for monopulse tracking – Amplitude Comparison Monopulse Radiating elements can be combined in 3 ways Sum, azimuth difference, and elevation difference patterns – Phase Comparison Monopulse Use top and bottom half of array for elevation Use right and left half of array for azimuth • Lens arrays (e.g. MOTR) would use amplitude monopulse – Four-port feed horn would be same as for dish reflector MOTR BMEWS Courtesy of MIT Lincoln Laboratory, Used with Permission
  • 53.
    Radar Systems Course53 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
  • 54.
    Radar Systems Course54 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Split Gate Range Tracking Early Gate Signal Difference Signal between Early and Late Range Gates Late Gate Early Gate Echo Pulse Late Gate Signal • Two gates are generated; one is an early gate, the other is a late gate. • In this example, the portion of the signal in the early gate is less than that of the late gate. • The signals in the two gates are integrated and subtracted to produce the difference error signal. • The sign of the difference indicates the direction the two gates have to be moved in order to have the pair straddle the echo pulse • The amplitude of the difference determines how far the pair of gates are from the centroid.
  • 55.
    Radar Systems Course55 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Multi Target Tracking in Range, Angle, and Doppler • Single target angle trackers (Dish radars) can be configured to track other targets in the radar beam – Useful for radars with moderate to wide beamwidths – Favorable geometry helpful • TRADEX and several other radars have multi-target trackers – Primary target is kept on boresight with standard monopulse angle tracker – Up to 10 other targets, in radar beamwidth, are tracked in range • Some other radars track in Doppler and in range along with tracking in angle
  • 56.
    Radar Systems Course56 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Outline • Introduction • Observable Estimation • Single Target Tracking – Angle tracking techniques Amplitude monopulse Phase comparison monopulse Sequential lobing Conical scanning – Range tracking – Servo systems • Multiple Target Tracking • Summary
  • 57.
    Radar Systems Course57 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Antenna Servo Systems • The automatic tracking of a target in angle employs a servo system that utilizes the angle error signals to maintain the pointing of the antenna in the direction of the target • The servo system introduces lag in the tracking that results in error – The lag error depends on the target trajectory Straight line, gradual turn, rapid maneuver • Type II Servo System often used in tracking radar – No steady state error when target velocity constant – Known as “zero velocity error system” • The effect of velocity and acceleration on a servo system can be described by the frequency response of the tracking loop
  • 58.
    Radar Systems Course58 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Servo Bandwidth • The tracking bandwidth of a servo system is that of a low pass filter • The bandwidth should be narrow to: Minimize the effects of noise,or jitter, Reject unwanted signal components Conical scan frequency or jet engine modulation Provide a smoothed output of the desired measured parameters • The bandwidth should be wide to: Follow rapid changes in the target trajectory or in the vehicle carrying the radar • The choice of servo bandwidth is usually a compromise – Sensitivity vs. tracking of maneuvering target • Tracking bandwidth may be made variable or adaptive Far range - angle rates low, low S/N (narrow bandwidth) Short range - angle rates large (wide bandwidth) Shorter ranges - Glint can be an issue (narrow bandwidth)
  • 59.
    Radar Systems Course59 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Bounds on Servo Resonant Frequency • The tracking bandwidth of a mechanical tracker should be small compared to the lowest natural frequency of the antenna and its structural foundation – This prevents the antenna from oscillating at its resonant frequency ServoResonantFrequency(Hz) Antenna Diameter (ft) 1 3 10 30 100 300 10 1 30 3 100 APG-66 SCR-584 FPS-16 FPQ-10 FPQ-6 FPS-49 Goldstone Haystack
  • 60.
    Radar Systems Course60 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Summary – Part 1 • A detailed description of the different radar observables and their estimation was presented – Observables - Range, angle, and Doppler velocity – Radar cross section issues were presented in a previous lecture – Resolution, precision and accuracy were discussed • The different techniques for single target angle tracking were discussed in detail, as well as their implementation – Amplitude monopulse – Phase comparison monopulse – Sequential lobing – Conical scanning • Range tracking techniques, as well as other related subjects were presented
  • 61.
    Radar Systems Course61 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Homework Problems • From Skolnik, Reference 1 – Problems 4.1, 4.3, 4.5, 4.9, 4.11, and 4.15
  • 62.
    Radar Systems Course62 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society References 1. Skolnik, M., Introduction to Radar Systems, McGraw-Hill, New York, 3rd Ed., 2001 2. Barton, D. K., Modern Radar System Analysis, Norwood, Mass., Artech House, 1988 3. Skolnik, M., Editor in Chief, Radar Handbook, New York, McGraw-Hill, 3rd Ed., 2008 4. Skolnik, M., Editor in Chief, Radar Handbook, New York, McGraw-Hill, 2nd Ed., 1990 5. Sherman, S. M., Monopulse Principles and Techniques, Norwood, Mass., Artech House, 1984 6. Barton, D. K. and Ward, H. R, Handbook of Radar Measurements, Norwood, Mass., Artech House, 1984
  • 63.
    Radar Systems Course63 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Acknowledgements • Dr Katherine A. Rink • Dr Eli Brookner, Raytheon Co.
  • 64.
    Radar Systems Course64 Parameter Estimation 1/1/2010 IEEE New Hampshire Section IEEE AES Society Part 2 • Introduction • Observable Estimation • Single Target Tracking • Multiple Target Tracking • Summary