introduction to radarmwj

Bullock Engineering Research Copyright 2014

1

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

Propagation Path Replicators

Phase Noise Test Systems

Service and Calibration

Bullock Engineering Research Copyright 2014

6

Introduction to RADAR

Webinar By Scott R. Bullock of Besser Associates, Inc.

Bullock Engineering Research www.BesserAssociates.com Copyright 2014

7

Scott R. Bullock [email protected]

BSEE BYU, MSEE U of U, PE, 18 US Patents, 22 Trade Secrets

Books & Publications

Transceiver and System Design for Digital Communications, 4th edition

http://iet.styluspub.com/Books/BookDetail.aspx?productID=395134

http://www.theiet.org/resources/books/telecom/tsddcfe.cfm

Broadband Communications and Home Networking

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, NY

Advanced Communications, ITT

Engineering 201E, PIMA

Key Designs

Radar Simulator for NWS China Lake Acquisition, Target Tracking, Missile Tracking, MTI

Navys 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 home

Miniature 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

Bullock Engineering Research www.BesserAssociates.com

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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

PRF determines the radars maximum detection range

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

RCS () - size and ability of a target to reflect radar energy m s = Projected cross section * Reflectivity * Directivity

The target radar cross sectional area depends on:

Airplanes physical geometry and exterior features

Direction of the illuminating radar

Transmitted frequency,

Material types of the reflecting surface.

Difficult to estimate

Equals the targets cross-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 s = pr2

Flat Plate s = 4pw2h2/l2

Corner Reflector s = 8pw2h2/l2

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 = l2/(4pR)2 LAtmos Lmulti

Transmitter

Reflector

Target Pt

Gt

Power at Target = Ptarg(i) = PtGtAfs= PtGt l2

(4pR)2

Power at Target = Ptarg = PtGtAfs = PtGt l2

Includes other losses Lt (4pR)2 Lt

Lt = LAtmos * Lmulti


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Radar Received

Power from Target

Afs = l2/(4pR)2

LAtmos Lmulti

Freespace

Attenuation Water

Vapor

Rain

Loss

Oxygen

Absorption

Multipath

Loss

Receiver

Reflector

Target

Gtarg= 4ps/l2

s = RCS

Gr

Pr

Ptarg


Ptarg(i) 4ps l2 Gr

l2 (4pR)2 Power received at Radar (ideal) = Pr(i) = Ptarg(i)Gtarg AfsGr =

Ptarg 4ps l2 Gr

l2 (4pR)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


Transmitter

Receiver

Reflector

Target

Duplexer

Gtarg= 4ps/l2

s = RCS

Pt Gt l2 4ps l2 Gr =

(4pR)2 l2 (4pR)2

Pt

Pr

Power at Target (Ideal) = Ptarg(i) = PtGtAfs= PtGt (l2/(4pR)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

PtGtGrl2s

(4p)3R4

PtG2l2s

(4p)3R4Ls

PtGtGrsc02

(4p)3f2R4 =

PtG2sc0

2

(4p)3f2R4Ls

=


Afs = l2/(4pR)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 (l2/(4pR)2)

Pr =

PtG2l2s

(4p)3R4Ls

PtG2sc0

2

(4p)3f2R4Ls

= Given: What is Pr in dBm?

f = 2.4 GHz, , l = .125

Pt = 100W

R = 1000m

Gt = Gr = 1000

Total 2-way loss Ls = 10

s= 140 m2

100(1000)2(.125)2(140)

(4p)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


Transmitter

Receiver

Reflector

Target

Duplexer

Gtarg= 4ps/l2

s = RCS

Gr

Pt

Pr

Gt


Afs = l2/(4pR)2

LAtmos Lmulti

Freespace

Attenuation Water

Vapor

Rain

Loss

Oxygen

Absorption

Multipath

Loss



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Free Space Attenuation

Forms of free-space attenuation depends on how it is used

Afs = (l/(4pR))2 will be less than 1 and multiplied

Afs = ((4pR)/l)2 will be greated than 1 and divided

Afs = 20log l/(4pR) = will be a negative number and added

Afs = 20log (4pR)/l = will be a positive number and subtracted

Important to determine if it is added or subtracted to avoid mistakes

Given:

Pt = 100W = 50dBm, l = .125, R = 1000m

Afs = (l/(4pR))2 = 98.9 x 10-12 need to multiply: Pr = 100W * 98.9 x 10-12 = 9.89 x 10-9

Afs = ((4pR)/l)2 = 1.01065 x 1010 need to divide: Pr = 100W/(1.01065 x 1010)= 9.89 x 10-9

Afs = 20log l/(4pR) = -100 dB need to sum: Pr = 50dBm + (-100dB) = -50dBm

Afs = 20log (4pR)/l = 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 l/(4pR)

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 l = wavelength

R = slant range

Ls = total two-way additional losses

s = 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 = PtG2l2s

(4p)3R4Ls

P(mW) = dBm or P(W) = dBw


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Radar Example dB

Power at Target = Ptarg = PtGtAfs= PtGt (l2/(4pR)2)

AfsdB = 10log(l2/(4pR)2) = 20log(l/(4pR) = 20log[(.125)/(4p1000)] = -100.05dB

Gtarg = 10log(4ps/l2) = 10log(4p*140/.1252) = 50.5dB

PtG2l2s

(4p)3R4Ls

PtG2sc0

2

(4p)3f2R4Ls

=

Given: What is Pr?

f = 2.4 GHz, , l = .125

Pt = 100W = 50dBm

R = 1000m

Gt = Gr = 1000 = 30dB

Total 2-way loss Ls = 10 = 10dB

s= 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


Transmitter

Receiver

Reflector

Target

Duplexer

Gtarg= 4ps/l2

s = RCS

Gr

Pt

Pr

Gt


Afs = l2/(4pR)2

LAtmos Lmulti

Freespace

Attenuation Water

Vapor

Rain

Loss

Oxygen

Absorption

Multipath

Loss



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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

Sinf = El/Rslant: Rslant = El/sinf

Cosf = Rgnd/Rslant: Rgnd = Rslant*cosf

f Given:

Elevation = 5000 ft

Angle = 300

Calculate Slant Range =

Rslant = El/sinf = 5000/sin(30) = 10,000 ft

What is the Ground Range =

Rgnd = Rslant*cosf = 10,000*cos(30) = 8660.25 ft

Rslant2 = Rgnd

2 + EL2: Rgnd = (Rslant

2 - 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*10

8 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 = PtGtGrl2s 1/4 = PtGtGrsc0

2 1/4

(4p)3SminLs (4p)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 = PtGtGrl2s

(4p)3R4Ls

Basic Radar Equation

R4 = PtGtGrl2s

(4p)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

Vary the PRF, depending radars operational mode

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 s 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 s (Rmin = 120 km)

ATC air surveillance radar: 1.5 s (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

Besser Associates Besser Associates, Inc. 2014 All rights reserved

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


48

Additional Slides If Needed


49

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*t)/2

Sr = range resolution as a distance between the

two targets

c0 = speed of light

t = transmitters pulse width


50

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


52

Pulse Compression

Improves Range Resolution

Using Spreading Techiques

Chirped FM Compression

Phase Shift Keying PSK Compression

Good Resolution

Good Resolution

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