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Bullock Engineering Research Copyright 2014
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Introduction to RADAR Webinar
By Scott R. Bullock
of
Besser Associates, Inc.
Sponsored by:
Eastern OptX Background
Test Solutions for: Radar Systems Transponders Altimeters
FMCW LPI
Digital Radios
Eastern OptX Background
A Veteran Owned Small Business Approved Suppler to the DoD and all Major Primes Operating in Moorestown NJ USA Since 1975. 15 Years Building Propagation Path Test Instruments. 26 Year History with Phase Noise Measurement Systems. More than 20 years of System Integration Experience. Calibration and Service Lab since 1999 currently supporting 20 year old field equipment.
Propagation Path Replicators
Propagation Path Replicators
Test Systems for Radar, Radar Ranges, and Radio Systems Operates with any signal waveform type, encryption, spread spectrum, and variable power. Uni and Bi Directional Systems High Dynamic Range (120 dB) Wide band 0.001 40 GHz Better than 1% Accuracy Replicate channel up to 200 Nautical Miles Doppler, Interferer Generation, Phase Modulator, and Multipath (fading)
Phase Noise Test Systems
Phase Noise Test Systems
6, 26, and 50 GHz Models Absolute and Residual Measurements Pulsed and CW Amplitude Noise Base Band Noise Lowest Noise Level Test Capability in the Industry (190 dBc/Hz) Single box solution
Altimeter Test Systems
Altimeter Test Systems
Universal Radar Altimeter Test System for all makes and models. For use in development, calibration, and production test application. FMCW (Swept CW. All types including constant difference frequency CDF). Compressed Pulse Radar Altimeter (CPRA, Satellite Altimeter). High Spatial Resolution Radar Altimeter (Topology Mapping). Low Probability of Intercept (LPI). Stealth altimeter for military aircraft.
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Scott R. Bullock [email protected]
BSEE BYU, MSEE U of U, PE, 18 US Patents, 22 Trade Secrets Books & Publications
th edition http://iet.styluspub.com/Books/BookDetail.aspx?productID=395134 http://www.theiet.org/resources/books/telecom/tsddcfe.cfm
http://sci.styluspub.com/Books/BookDetail.aspx?productID=369239 http://digital-library.theiet.org/content/books/te/sbte002e
Multiple Articles in Microwaves & RF, MSN Seminars - Raytheon, L-3, Thales, MKS/ENI, CIA, Titan, Phonex, NGC, Others
Courses for Besser Associates Introduction to RADAR - http://www.besserassociates.com/outlinesOnly.asp?CTID=253 Introduction to Wireless Communications Systems - http://www.bessercourse.com/outlinesOnly.asp?CTID=235 Transceiver and Systems Design for Digital Communications - http://www.bessercourse.com/outlinesOnly.asp?CTID=208 Cognitive Radios, Networks, and Systems for Digital Communications - http://www.bessercourse.com/outlinesOnly.asp?CTID=251
College Instructor Graduate Presentation on Multiple Access to Polytechnic, Farmingdale//Brooklyn, NYAdvanced Communications, ITT Engineering 201E, PIMA
Key Designs Radar Simulator for NWS China Lake Acquisition, Target Tracking, Missile Tracking, MTI
IntegratedTopside INTOP Integrate Radar with EW, EA, Comms Radar Comms using CP-PSK Modulated Pulses for the SPY-3 Radar and PCM/PPM
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RAdio Detecting And Ranging RADAR
RADAR is a method of using electromagnetic waves to
determine the position (range and direction), velocity and identifying characteristics of targets.
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Radar Applications
Military Search and Detection Targeting and Target Tracking Missile Guidance Fire Control Acquisition, Track Airborne Intercept Ground and Battle field Surveillance Air Mapping Systems Submarine and Sub-Chasers
Commercial Weather, Navigation, Air Traffic Control Space and Range Road and Speeding Biological Research Bird and Insect Surveillance and Tracking Medical diagnosis, organ movements, water condensation in the lungs, monitor heart rate and pulmonary motion, range(distance), remote sensor of heart and respiration rates without electrodes, patient movement and falls in the homeMiniature Seeing aids, early warning collision detection and situational awareness
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Two Basic Radar Types
Pulse Radar Transmits a pulse stream with a low duty cycle Receives pulse returns from targets during the time off or dead time between pulses
Continuous Wave Radar Sends out a continuous wave signal and receives a Doppler frequency for moving targets
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Pulse Vs. Continuous Wave
Pulse Radar Single Antenna Determines Range & Altitude Susceptible To Jamming Physical Range Determined By Pulse Width PW and Pulse Repetition Frequency PRF Low average power Time synchronization
Continuous Wave Radar Based on Doppler Requires 2 Antennas No Range or Altitude Information High SNR More Difficult to Jam But Easily Deceived Simpler to operate, timing not required
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Pulsed Radar
Most radar systems are pulsed Transmit a pulse and then listen for received signals, or echoes Avoids problem of a sensitive receiver simultaneously operating with a high power transmitter. Transmits low duty cycle, short duration high-power RF- pulses Time synchronization between the transmitter and receiver of a radar set is required for range measurement.
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Pulse Radar Modulation
100% Amplitude Modulation AM ON/OFF keying Turn on/off a Carrier Oscillator Pulse width is how long the carrier is on Pulse Repetition Frequency is how fast the carrier is turned on
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Radar Turns on/off the Carrier Frequency
Pulse Width = 1us
Time between pulses = PRI = 7us = 1/PRF = 143 kHz
V
t
Burst of Carrier Frequency Radar burst Low duty cycle, high power Duty cycle = time on/time off * 100 a percentage Above example approx. 1/6 * 100 = 16%
carrier wave = 4MHz
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Radar Burst of Frequency Pulse Modulated On/Off Keying t
V
Oscillator
Modulator On/Off Switch
Continuous Waveform - CW
Pulse Train: PRF Radar Pulses
V
t PW
PRI = PRT
PRF = 1/PRI
t
V
PW
PRI = PRT
PRF = 1/PRI
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Pulse Characteristics
Pulses are repeated at the Pulse Repetition Frequency or PRF PRF is the number of pulses per second Pulse Repetition Indicator PRI is the time between pulses Pulse Repetition Time PRT is the same as PRI PRT = PRI = 1/PRF
Pulse Width PW - amount of time that the radar is transmitting Pulse Width (PW) determines the minimum range resolution
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Pulse Distortion
P1
PRI = 1/PRF Long P1 returns cause distortion to P2 returns
t
V
Long returns from P1 causes distortion to the returns of P2
P2
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Basic RADAR
Transmit Radar Pulse
Radar Directional Antenna
Target
Reflection off a Target
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Basic Radar Diagram
Transmitter Reflective Radar
Surface
Transmit Channel
Low Noise Receiver
Receive Channel
RADAR TARGET
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Radar Path Budget
Tracks Signal & Noise Levels from Radar to Target back to Radar Power Out (PA), Tx Losses, Channel Losses, Target Reflectivity, Channel Losses, Rx Losses, Rx Detect S/N Required S/N
Radar Budget - Allocation of Power and Noise Radar Tx PA to Radar Rx Detector (LNA) Used in Solving Tradeoffs
Size, cost, range Radar pulses are reflected off targets that are in the transmission path
Targets scatter electromagnetic energy Some of the energy is scattered back toward the radar.
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Effective Isotropic Radiated Power EIRP
EIRP = Effective Isotropic Radiated Power = RF Power * Antenna Gain
RF Power
Gain
RF Power
Target
Target
ERP = Effective Radiated Power EIRP = ERP + Gdipole (2.14dB) ERP = EIRP - Gdipole (2.14dB)
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Sun Focusing Sun Rays
To Increase Power
Focusing Radio Waves To Increase
Power
Magnifying Glass
Directional Antenna
Receiver
Focusing Increases Power To Provide Gain
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Radar Cross Section RCS
- size and ability of a target to reflect radar energy m² = Projected cross section * Reflectivity * Directivity
The target radar cross sectional area depends on:
Direction of the illuminating radar Transmitted frequency, Material types of the reflecting surface.
Difficult to estimate -sectional area theoretically
Not all reflected energy is distributed in all directions Some energy is absorbed Usually measured for accurate results
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Radar RCS Patterns
Sphere = r2
Flat Plate = 4 w2h2/
Corner Reflector = 8 w2h2 2
Similar to Antenna Gains
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Radar Transmitter Power to Target
Freespace Attenuation
Water Vapor
Rain Loss
Oxygen Absorption
Multipath Loss
EIRP
Afs = 2/(4 R)2 LAtmos Lmulti
Transmitter
Reflector Target
Pt
Gt
Power at Target = Ptarg(i) = PtGtAfs= PtGt 2
(4 R)2
Power at Target = Ptarg = PtGtAfs = PtGt 2 Includes other losses Lt (4 R)2 Lt
Lt = LAtmos * Lmulti
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Radar Received Power from Target
Afs = 2/(4 R)2 LAtmos
Lmulti
Freespace Attenuation
Water Vapor
Rain Loss
Oxygen Absorption
Multipath Loss
Receiver
Reflector Target
Gtarg= 4 / 2
= RCS
Gr Pr
Ptarg
Lt = LAtmos * Lmulti
Ptarg(i) 4 2 Gr 2 (4 R)2
Power received at Radar (ideal) = Pr(i) = Ptarg(i)Gtarg AfsGr =
Ptarg 4 2 Gr 2 (4 R)2 Lt
Power at Radar = Pr= PtargGtarg AfsGr = (Includes losses) Lt
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Radar Antenna Gain and Channel Losses
Freespace Attenuation
Water Vapor
Rain Loss
Oxygen Absorption
Multipath Loss
EIRP
Afs = 2/(4 R)2 LAtmos Lmulti
Transmitter
Receiver
Reflector Target
Duplexer
Gtarg= 4 / 2
= RCS
Pt Gt 2 4 2 Gr =
( R)2 2 (4 R)2
Pt
Pr
Power at Target (Ideal) = Ptarg(i) = PtGtAfs= PtGt ( 2/(4 R)2)
Power at Radar (Ideal) = Pr(i) = Ptarg(i)Gtarg AfsGr =
Pr = One-way Loss: Lt = LAtmos * Lmulti Two-way Losses = Lt * Lt = Lt
2 = Ls
Including other losses in the path
Assume Antenna Gain Gt = Gr
PtGtGr2
3R4
PtG2 2
3R4Ls
PtGtGr c02
3f2R4 =
PtG2 c02
3f2R4Ls
=
Lt = LAtmos * Lmulti
Afs = 2/(4 R)2 LAtmos
Lmulti
Freespace Attenuation
Water Vapor
Rain Loss
Oxygen Absorption
Multipath Loss
Lt = LAtmos * Lmulti Gr
Gt
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Radar Example
Power at Target = Ptarg = PtGtAfs= PtGt ( 2/(4 R)2)
Pr = PtG2 2
3R4Ls
PtG2 c02
3f2R4Ls = Given: What is Pr in dBm?
f = 2.4 GHz, , = .125 Pt = 100W R = 1000m Gt = Gr = 1000 Total 2-way loss Ls = 10
= 140 m2
100(1000)2(.125)2(140)
3 (1000)4(10) Pr = =1.10235*10-8W = 1.10235*10-5mW
Prdbm = 10log(1.10235*10-5) = -49.6 dBm
Freespace Attenuation
Water Vapor
Rain Loss
Oxygen Absorption
Multipath Loss
EIRP
Afs = 2/(4 R)2 LAtmos Lmulti
Transmitter
Receiver
Reflector Target
Duplexer
Gtarg= 4 / 2
= RCS
Gr
Pt
Pr
Gt
Lt = LAtmos * Lmulti
Afs = 2/(4 R)2 LAtmos
Lmulti
Freespace Attenuation
Water Vapor
Rain Loss
Oxygen Absorption
Multipath Loss
Lt = LAtmos * Lmulti
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Free Space Attenuation
Forms of free-space attenuation depends on how it is used Afs = ( /(4 R))2 will be less than 1 and multiplied Afs = ((4 R)/ )2 will be greated than 1 and divided Afs = 20log /(4 R) = will be a negative number and added Afs = 20log (4 R)/ = will be a positive number and subtracted Important to determine if it is added or subtracted to avoid mistakes
Given:
Pt = 100W = 50dBm, = .125, R = 1000m Afs = ( /(4 R))2 = 98.9 x 10-12 need to multiply: Pr = 100W * 98.9 x 10-12 = 9.89 x 10-9
Afs = ((4 R)/ )2 = 1.01065 x 1010 need to divide: Pr = 100W/(1.01065 x 1010)= 9.89 x 10-9
Afs = 20log /(4 R) = -100 dB need to sum: Pr = 50dBm + (-100dB) = -50dBm Afs = 20log (4 R)/ = 100 dB need to subtract: Pr = 50dBm - 100dB) = -50dBm
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Two-Way Radar Losses
Two-way free space loss used twice Once for the radar transmitter to target path Once for the target to radar receiver path Free Space Loss 2*Afs = 2* 20log /(4 R)
Two-way Losses in Radar in dB Atmospheric loss 2* Latmos Multipath loss 2* Lmult
T/R switch or Circulator loss 2* Ltr Antenna loss, Polarization, Mis-pointing, Radome 2* Lant Implementation loss 2*Li Losses in dB: Ltotal = 2* Latmos + 2* Lmult + 2* Ltr + 2* Lant + 2* Li
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RADAR Equation to Assess Radar Performance
P r = Radar received power P t = Radar transmitted power G t = Transmitter antenna gain G r = Receiver antenna gain G2 = Gr Gt assumes the same antenna at the radar = wavelength
R = slant range Ls = total two-way additional losses
= radar cross section of the target RCS
Log Form
Pr = PtG tG r Afs AfsGtarg1/Ls
10logPr = 10logPt + 10logG + 10logG + 10logAfs + 10logAfs + 10logGtarget - 10log(Ls)
Pr dBm = Pt dBm + 2GdB + 2Afs dB + Gtarget dB Ls dB
Pr = PtG2 2
3R4Ls
P(mW) = dBm or P(W) = dBw
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Radar Example dB
Power at Target = Ptarg = PtGtAfs= PtGt ( 2/(4 R)2)
AfsdB = 10log( 2/(4 R)2) = 20log( /(4 R) = 20log[(.125)/(4 1000)] = -100.05dB Gtarg = 10log(4 / 2) = 10log(4 /.1252) = 50.5dB
PtG2 2
3R4Ls
PtG2 c02
3f2R4Ls
=
Given: What is Pr? f = 2.4 GHz, , = .125 Pt = 100W = 50dBm R = 1000m Gt = Gr = 1000 = 30dB Total 2-way loss Ls = 10 = 10dB
= 140 m2 Pr dBm = Pt dBm + 2GdB + 2Afs dB + Gtarget dB Ls dB
Pr dBm = 50dBm + 2*30dB + 2*-100.05 dB + 50.5 dB 10dB = -49.6dBm
Freespace Attenuation
Water Vapor
Rain Loss
Oxygen Absorption
Multipath Loss
EIRP
Afs = 2/(4 R)2 LAtmos Lmulti
Transmitter
Receiver
Reflector Target
Duplexer
Gtarg= 4 / 2
= RCS
Gr
Pt
Pr
Gt
Lt = LAtmos * Lmulti
Afs = 2/(4 R)2 LAtmos
Lmulti
Freespace Attenuation
Water Vapor
Rain Loss
Oxygen Absorption
Multipath Loss
Lt = LAtmos * Lmulti
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Range Determination
Range calculation uses time delay between objects Time delay is measured from source to reflector and back Time delay divided by two to calculate one way range
Sound-wave reflection
Shout in direction of a sound-reflecting object and hear the echo Calculate two-way distance using speed of sound 1125 ft/sec in air Measure two way delay of 5 seconds Range = 1125ft/sec x 5/2 = 2812ft
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Sound Wave Reflection
Hi
Hi
Determine the distance using range formula Listen to multiple echoes off difference distances
Best echo effects when the yell is short short pulse width
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Sound Wave Reflection
Hi
Hi
Determine the distance using range formula Listen to multiple echoes off difference distances
Best echo effects when the yell is short short pulse width
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Radar Range Calculation
Radar uses electromagnetic energy pulses Pulse travel at the speed of light C0 Reflects off of a surface and returns an echo back to the radar Calculates the two-way distance or slant range Slant range = line-of-sight distance from radar to target Takes in account the angle from the earth Ground range = horizontal distance from radar to target Slant range calculated using ground range and elevation Radar energy to the target drops proportional to range squared. Reflected energy to the radar drops by a factor of range squared Received power drops with the fourth power of the range
Need very large dynamic ranges in the receive signal processing
Need to detect very small signals in the presence of large interfering signals
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Slant Range
Slant Range = Rslant
Radar Directional
Antenna
Target
Ground Range = Rgnd
Elevation = EL
Rslant2 = Rgnd
2 + EL2: Rslant = (Rgnd2 + EL2)1/2
Sin = El/Rslant: Rslant = El/sin
Cos = Rgnd/Rslant: Rgnd = Rslant*cos
Given: Elevation = 5000 ft Angle = 300
Calculate Slant Range = Rslant = El/sin 5000/sin(30) = 10,000 ft What is the Ground Range = Rgnd = Rslant*cos = 10,000*cos(30) = 8660.25 ft Rslant
2 = Rgnd2 + EL2: Rgnd
= (Rslant2 - EL2) 1/2 = (10,0002 - 50002) 1/2 = 8660.25ft
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Range Calculation
Electromagnetic energy pulse travels at the speed of light C0
R = (tdelay * C0)/2 R = slant range tdelay = two way time delay Radar-Target-Radar C0 = speed of light = 3*108 m/s Given: tdelay = 1ms C0 = 3x108 m/sec Calculate Slant Range = R = (1ms * 3*108 m/s)/2 = 150km
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Radar Range Equation
Rmax = PtGtGr2 = PtGtGr c0
2 3SminLs
3f2SminLs
Double the range requires 16 times more transmit power Pt
Radar detection range = the maximum range at which a Target has a high probability of being detected by the radar
Pr = S = PtGtGr2
3R4Ls
Basic Radar Equation
R4 = PtGtGr2
3SLs
Radar Range Equation (solving for Rmax range for minimum signal Smin):
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Range Ambiguity
Caused by strong targets at a range in excess of the pulse repetition indicator or time Pulse return from the first pulse comes after the second pulse is sent This causes the range to be close instead of far away Radar does not know which pulse is being returned Large pulse amplitude and higher PRF amplifies the problem The maximum unambiguous range for given radar system can be determined by using the formula:
Rmax = (PRI T) * C0/2 PRI = pulse repetition indicator T = pulse width time C0 = speed of light
Example: PRI = 1msec, T = 1us Calculate Max unambiguous Range = (1ms 1us)*3*108/2 = 149.9km
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Range Ambiguity
P1 P2
PRI Range Ambiguities
t
V
Rmax = (PRI PW) * C0/2
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Range Ambiguity Mitigation
Decreasing the PRF reduces the range ambiguity Longer the time delay, higher free-space loss, smaller the return
Transmit different pulses at each PRF interval Higher receiver complexity Requires multiple matched filters at each range bin and at each azimuth and elevation Increases rate of the DSP required for each separate transmit pulse and matched filter pair
Requires changing the system parameters Used most often to mitigate range ambiguity Desired returns from the second pulse move with the PRF Undesired returns do not move since they are reference to the first pulse
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Minimum Detectable Range Example
P1
t
V R1 R2
R3
Minimum Detectable Range Pulse
Does not interfere with the Radar pulse
Tmin for Rmin = Pulsewidth
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Minimum Detectable Range
Radar minimum detectable range return cannot come back during the pulse width
Rmin = (T + Trecovery)*C0/2
T = Pulse width, Trecovery = time for pulse to recover
Very close range targets equivalent to the pulse width not be detected Typical value of 1 for the pulse width of short range radar corresponds to a minimum range of about 150 m Longer pulse widths have a bigger problem Typical pulse width T assuming recovery time of zero: Air-defense radar: up to 800 (Rmin = 120 km) ATC air surveillance radar: 1.5 (Rmin = 225 m)Surface movement radar: 100 ns (Rmin = 15 m)
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Plan Position Indicator (PPI)
The return is displayed on a Plan Position Indicator (PPI)
Rotating Search Radars illuminates the targets on the PPI according to the angle received Range is displayed according to the distance from the center of the PPI Uses a range gate to lock on the range of the PPI
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PPI and A-Scope Displays
N
S
00
900
1800
2700
AoA = 770
Range Gate
PPI A-Scope
Range Gate
V
t
www.BesserAssociates.com
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Thank you for Attending !
For more information on this subject please consider attending the live Besser course, Introduction to Radar, March 2 to 4,
2015, in Costa Mesa, California. Contact Besser Associates at [email protected] or
visit us at www.BesserAssociates.com
Sponsored by: online at www.eastern-optx.com
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Additional Slides If Needed
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Range Resolution
Range resolution - separate two equal targets at the same bearing but different ranges
Depends on the width of the transmitted pulse Types and sizes of targets Efficiency of the receiver and indicator
Pulse width is the primary factor in range resolution Able to distinguish targets separated by one-half the pulse width Basically the same as minimum detectable range Theoretical range resolution is: Sr = (c0* )/2
Sr = range resolution as a distance between the two targets c0 = speed of light = transmitters pulse width
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Pulse Compression Range Resolution
In pulse compression the range-resolution is given by the bandwidth of the transmitted pulse (Btx), not by its pulse width
Sr = > c0/2Btx
Sr = range resolution as a distance between the two targets c0 = speed of light Btx = band width of the transmitted pulse
Allows very high resolution with long pulses with a higher average power
Given: Btx = 20 MHz Calculate Range resolution Sr =
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Basic Radar Range Resolution
CW without Compression
CW without Compression
Poor Resolution
Good Resolution
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Pulse Compression Improves Range Resolution Using Spreading Techiques
Chirped FM Compression
Phase Shift Keying PSK Compression
Good Resolution
Good Resolution