radar fall2015 (3)

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NTRODUCT ON

CONTRACTION OF THE WORDS RADIODETECTION AND RANGING

RADAR IS AN ELECTROMAGNETIC SYSTEM FOR THE DETECTION AND LOCATION OF REFLECTING

OBJECTS SUCH AS AIRCRAFT, SHIPS, SPACECRAFT,VEHICLES , PEOPLE AND NATURAL ENVIRONMENT

OPERATES BY RADIATING ENERGY INTO SPACE AND DETECTING THE ECHO SIGNAL REFLECTED

FROM AN OBJECT OR TARGET

REFLECTED ENERGY INDICATES PRESENCE,LOCATION AND OTHER INFORMATION, HEIGHT ETC

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NTRODUCT ON

Radar can perform its function at long

or short distances and under

conditions impervious to optical andinfrared sensors. It can operate in

darkness, haze, fog, rain and sno.

Its a!ilit" to measure distance ith

high accurac" in all eather is one of

the most important attri!utes.

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NTRODUCT ON

#ome Radars have to detect targets at

ranges as short as the distance from

!ehind the ickets to the !olersdeliver" $to measure the speed of a

deliver"%, hile other radars have to

operate over distances as great as the

distances to the nearest planets.

Thus, a radar might !e small enough

to hold in the palm of one hand or

larger than a foot!all field .

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NTRODUCT ON

Radar targets might !e aircraft, ships,

or missiles& !ut radar targets can also

!e people, !irds, insects,precipitation, clear air tur!ulence,

ionized media, land features

$vegetation, mountains, roads, rivers,

airfields, !uildings, fences, poer '

line poles%, sea, ice, ice!ergs, !uo"s,

underground features, meteors,

aurora, spacecraft and planets.

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NTRODUCT ON

Radar is used to detect aircraft, guide

supersonic missiles, o!serve and

track eather patterns, and controlflight traffic at airports. It is also

used in !urglar alarms, garage ' door

openers, and police speed detectors.

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NTRODUCT ON

Radar s"stems provided the ma(orincentive for the development of

microave technolog" !ecause the"

give !etter resolution for radar

instruments at higher fre)uencies. Onl"

the microave region of the spectrum

could provide the re)uired resolution

ith antennas of reasona!le size. Thea!ilit" to focus a radiated ave sharpl"

is hat makes microaves so useful in

radar applications.

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NTRODUCT ON

In addition to measuring the range toa target as ell as its angular

direction, a radar can also find the

relative velocit" of a target either !"determining the rate of change of the

range measurement ith time or !"

e*tracting the radial velocit" from the

Doppler fre)uenc" shift of the echosignal.

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NTRODUCT ON

If the location of a moving target ismeasured over a period of time, the

track, or tra(ector", of the target can !e

found from hich the a!solute velocit"

of the target and its direction of travel

can !e determined and a prediction can

!e made as to its future location.

+roperl" designed radars can determinethe size and shape of a target and

might even !e a!le to recognize one

t"pe or class of target from another.

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ELECTROMAGNETIC SPECTRUM

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RADIO DETECTION AND

RANGING

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INTRODUCTION

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INTRODUCTION

RADAR IS A CLASSIC EXAMPLE OF ANELECTRONIC ENGINEERING SYSTEM THATUTILIZES MANY OF THE SPECIALIZEDELEMENTS OF TECHNOLOGY PRACTICED BYELECTRICAL ENGINEERS , INCLUDINGSIGNAL PROCESSING, DATA PROCESSING,WAVEFORM DESIGN, ELECTROMAGNETIC

SCATTERING, DETECTION, PARAMETERESTIMATION, INFORMATION EXTRACTION,ANTENNAS, PROPAGATION, TRANSMITTERS

AND RECEIVERS

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BASIC PRINCIPLE

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BASIC PRINCIPLE

generates EM wave radiated in space by antenna.

Portion of energy intercepted by the

target and re-radiated in many directions.

Re-radiation directed back towards radar

collected by radar antenna – delivered to

Receiver

Processed to detect presence of target and

determine its location.

Single antenna used time shared basis when

radar waveform repetitive series of pulses.

T x

T x

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BASIC PRINCIPLE

Range or distance to a target found by measuring the time it takes for the radar

signal to travel to the target and return back.

argets location in angle can be found from the direction the narrow beamwidth radar

antenna points when the received signal is of

ma!imum amplitude.

"f target is in motion – than shift of fre#uency

determined.

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PRINCIPLES

$ Radar opra!" o# !$ %,&&& !o '&,&&& MH()r*+#- .a#d"/ 0"+pr $12$ )r*+#- SHF3

$ E4!ro5a2#!1 #r2- rad1a!1#2 o+!6ard )ro5 a"o+r 1" r7!d .a8 .- o.9!" 1# 1!" pa!$/

$ T$ !15 d1:r# .!6# !ra#"51""1o# 0!ra3a#d r7!1o# 0$o3 1" 5a"+rd 21;1#2 a#a+ra! 1#d1a!1o# o) a# o.9!" d1"!a#/

$ D1"!a#, a(15+!$, a#d 4;a!1o# a# . +"d !o<= !$ o.9!" po"1!1o# 1# !$r d15#"1o#a4"pa/

$ S12#a4 !151#2 1" r1!1a4 !o a+ra-/ 0o#51ro"o#d rror r"+4!" 1# a d1"!a# rror o)a45o"! >&&)!/3

$ A" a r"+4! po"1!1o# a+ra- 1" d1r!4- r4a!d !o!$ a+ra- o) !$ !151#2 d;1 +"d/

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What information RADAR can give

$ Tar2! ra#2 0d1"!a#3$ Tar2! $12$! 0a4!1!+d3$ Tar2! "pd$ Tar2! 1d#!1!-

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!OW RADAR WOR"S$ A radar "-"!5 02ro+#d?.a"d3 $a" a !ra#"51!!r

!$a! 51!" rad1o 6a;" or 51ro6a;" "12#a4/

$ T$ "12#a4 $1! a1rp4a# a#d r7! .a8/

$ Gro+#d?.a"d radar p18" +p r7!d "12#a4 d+r1#2a .ra8 .!6# !ra#"51""1o#"/

$ T$ !15 !a8# )or !$ r7!d "12#a4 !o r!+r#

.a8 #a.4" a o5p+!r a4+4a! $o6 )ar !$o.9! 1" 0ra#23/

$ T$ a1rra)! da!a !$# "#! a#d "$o6# o# a RadarD1"p4a-/

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Mo"! o#;#!1o#a4 a1rra)! $a; a ro+#dd "$ap/ T$1" "$ap ra!" a;r- @1#! radar r7!or/ Ma#" !$a! #o 5a!!r 6$r !$ radar"12#a4 $1!" !$ p4a#, "o5 o) !$ "12#a4 2!" r7!d .a8

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T#PES O$ RADAR

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T#PES O$ RADAR

%ig& ' – band S(R image of )-*+ aircraft sitting

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T#PES O$ RADAR

%ig& "S(R image of a ship with ' – band radar

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T#PES O$ RADAR

"S(R image of a commercial ship ,/// ton0 obtained with an ' – band radar having + meter

resolution. he vertical scale in this image is slightly

e!aggerated. 1ote that 2radar eyes3 are not 2optical

eyes3 yet useful information can be obtained from aseries of such images. Pitch motion causes top of

masts to have higher velocity than the bottom of the

masts or superstructure. hese differences invelocity causes different 4oppler shifts. Resolution

in 4oppler allows masts to be imaged. (lso Roll

and 5aw motion provide height information6 etc .

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$!!p6a!$r/#oaa/2o;radarrad1#)orad1#)o/$!54

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% Bi&tatic ' !$ !ra#"51! a#d r1; a#!##a" ar a!d1:r#! 4oa!1o#" a" ;16d )ro5 !$ !ar2! 0/2/, 2ro+#d !ra#"51!!r a#da1r.or# r1;r3/

% Mono&tatic !$ !ra#"51!!r a#d r1;r aro4oa!d a" ;16d )ro5 !$ !ar2! 01//, !$ "a5 a#!##a 1" +"d !o !ra#"51!

a#d r1;3/

% ()a&i*mono&tatic !$ !ra#"51! a#d r1;a#!##a" ar "412$!4-

"para!d .+! "!144 appar !o . a! !$ "a5 4oa!1o#a" ;16d )ro5 !$

RADAR ANTENNA

CON$IGURATION

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Bi&tatic

TARGET

T R A N

S M I T T E D

P U L S E

R E $ L E

C T E D

P U L S E

RECEI+ER ANTENNA

TRANSMITTER ANTENNA

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Mono&tatic

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TARGET

T R A N

S M I T T E D

W A +

E

R E $ L E C T E D

W A + E

RECEI+ER ANTENNA

TRANSMITTER ANTENNA ()a&i * mono&tatic

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RANGE TO A TARGET

MA,IMUM UNAMBIGUOUS

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MA,IMUM UNAMBIGUOUSRANGE

MA,IMUM UNAMBIGUOUS

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MA,IMUM UNAMBIGUOUSRANGE

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UNAMBIGUOUS RANGE

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RADAR WA+E$ORMS

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RADAR WA+E$ORMS

are separated a distance half this value or . The factor of one –half results from the two –

way travel of the radar wave, eg when τ = 1 μs,

two equal size targets can e resolved if they are

separated y 1!" meters.

# very long pulse is needed for some long range

radars to achieve sufficient energy to detect small

targets at long range – long pulse has poorresolution in range dimension – pulse compression

used to otain resolution of a short pulse.

2

τ c

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RADAR WA+E$ORMS $ontinuous wave %$&' waveforms have also een used in

radar. (ince they have to receive while transmitting, $&

radars depend on the doppler frequency shift of the echo

signal, caused y a moving target, to separate in the

frequency domain the wea) echo signal from the large

transmitted signal and the echoes from fi*ed clutter %land,

sea, weather', as well as to measure the radial velocity of

the target.

# simple $& radar does not measure range. $an otainrange y modulating the carrier with frequency or phase

modulation, eg +-$& waveform used in radar altimeter

that measures height %altitude' of an aircraft aove the

earth.

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RADAR WA+E$ORMS

ulse radars that e*tract the /oppler frequencyshift are called either Moving Target Indication

%T0' or pulse doppler radars, depending on their

particular values of pulse repetition frequency and

duty cycle.

#n T0 radar has a low prf and a low duty cycle.

# pulse doppler radar, on the other hand, has a

high prf and a high duty cycle – discuss later. #lmost all radars designed to detect aircraft use

the doppler frequency shift to reect large

unwanted echoes from stationary clutter.

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PULSE WA+E$ORM

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BASIC RADAR E(UATION

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Satellite

Communications, 2/E .- T15o!$- Pra!!, C$ar4"

Bo"!1a#, Jr5- A44#+!!Cop-r12$! &&% Jo$#

$ig)re -./ 01. 2324F4+= d#"1!- prod+d .- a# 1"o!rop1 "o+r/

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Satellite

Communications, 2/E .- T15o!$- Pra!!, C$ar4"

Bo"!1a#, Jr5- A44#+!!Cop-r12$! &&% Jo$#

$ig)re -.5 01. 23/4Po6r r1;d .- a# 1da4 a#!##a 61!$ ara A 5/ I#1d#! 7+= d#"1!- 1" F Pt πR W5/ R1;d po6r 1" Pr F X A Pt AπR W/

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F12 ,a0 Single transmission path with parameters used in %riis

transmission formula.

,b0 and ,c0 4ouble-path geometry used in obtaining radar e#uation.

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A "!a4!$ a1rra)! 1" 5ad +p o) o5p4!4- 7a!

"+r)a" a#d ;r- "$arp d2"/ W$# a radar "12#a4$1!" a "!a4!$ p4a#, !$ "12#a4 r7!" a6a- a! a#a#24/ S+r)a" o# a "!a4!$ a1rra)! a4"o a# a."or.radar #r2- a" 644/ So, !$1" a1rra)! .o5 1#;1"1.4/

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Ho6;r, "o5 5141!ar- a1rra)! ard"12#d a#d o#"!r+!d !o . #o#?

r7!1; ? !$ "o?a44d "!a4!$

a1rra)!/

B*/ S1irit &tea6th

7om7er of the U.SAir $orce

An $*228 Nightha9: &tea6th &tri:e aircraft

$*// Ra1tor

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RDR CRO## #-CT ON

The a!ilit" of a target to scatter $or

reflect% energ" is characterized !" its

scattering cross section /0 $alsocalled the radar cross section %. The

scattering cross section has the units

of area and can !e measurede*perimentall".

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RDR CRO## #-CT ON

The sc ttering cross section is

the e)uivalent area intercepting the

amount of poer that, henscattering isotropicall", produces at

the radar a poer densit" that is e)ual

to that scattered or $reflected% !" the

actual target.

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1# C RDR -2UT ON

The radar cross section has units ofarea, !ut it can !e misleading to

associate the radar cross section

directl" ith the target0s ph"sicalsize. Radar cross section is more

dependent on the target0s shape

than on its ph"sical size as ill !e

discussed later.

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1# C RDR -2UT ON

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S C ( O

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1# C RDR -2UT ON

-) $3.4%& or the effective area is heldconstant, as implied !" -) $3.35%. 6or

-) $3.7% to !e independent of

fre)uenc", to antennas have to !eused. The transmitting antenna has

to have a gain independent of

avelength and the receiving

antenna has to have an effective

aperture independent of avelength.

$This is seldom done.%

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1# C RDR -2UT ON

These simplified versions of the radare)uation do not ade)uatel" descri!e the

performance of actual radars. 8an"

important factors are not e*plicitl" included.

The simple form of the radar range e)uationpredicts too high a value of range,

sometimes !" a factor of to or more. 9ater

the simple form of the radar e)uation is

e*panded to include other factors ' e)uationthan !ecomes in !etter agreement ith

o!served range performance of actual

radars.

RADAR BLOC"

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RADAR BLOC"DIAGRAM

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1# C +RT# O6

RDR

6igure $#lide :3% is a ver" elementar"!asic !lock diagram shoing the

su!s"stems usuall" found in a radar.

The Transmitter , hich is shon as apoer amplifier, generates a suita!le

aveform for the particular (o! the

radar is to perform. It might have an

average poer as small as milliatts or

as large as megaatts. $The average

poer is a far !etter..

;contd<

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1# C +RT# O6

RDR

Indication of the capa!ilit" of a

radar0s performance than is its

peak poer.% 8ost radars use a

short pulse aveform so that a

single antenna can !e used on a

time ' shared !asis for !oth

transmitting and receiving.

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1# C +RT# O6 RDR

The function of the duple*er is to

allo a single antenna to !e used

!" protecting the sensitive

receiver from !urning out hile

the transmitter is on and !"

directing the received echo signalto the receiver rather than to the

transmitter.

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1# C +RT# O6 RDR

The antenna is the device that allosthe transmitted energ" to !e propagated

into space and then collects the echo

energ" on receive. It is almost ala"s a

directive antenna, one that directs theradiated energ" into a narro !eam to

concentrate the poer as ell as to

allo the determination of the direction

to the target. n antenna that produces

a narro directive !eam on transmit=.

;contd<

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1# C +RT# O6 RDR

Usuall" has a large area onreceive to allo the collection of

eak echo signals from the

target. The antenna not onl"

concentrates the energ" on

transmit and collects the echo

energ" on receive, !ut it also acts

as a spatial filter to provide angle

resolution and other capa!ilities.

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1# C +RT# O6 RDR

The Receiver amplifies the eak receivedsignal to a level here its presence can !e

detected. 1ecause Noise is the ultimate

limitation on the a!ilit" of a radar to make

a relia!le detection decision and e*tractinformation a!out the target ' care is

taken to insure that the receiver produces

ver" little noise of its on. t themicroave fre)uencies, here most

radars are found,

;contd<

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1# C +RT# O6 RDR

The Noise that affects radar performanceis usuall" from the first stage of the

receiver, shon in 6ig $slide :3% as a lo '

noise amplifier. 6or man" radar

applications here the limitation todetection is the unanted radar echoes

from the environment $called clutter %, the

receiver needs to have a large enoughd"namic range so as to avoid having the

clutter echoes

;contd<

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1# C +RT# O6 RDR

adversel" affect detection of antedmoving targets !" causing the receiver to

saturate. The d"namic range of a

receiver, usuall" e*pressed in deci!els, is

defined as the ratio of the ma*imum tothe minimum signal input poer levels

over hich the receiver can operate ith

some specified performance. Thema*imum signal level might !e set !" the

non ' linear effects of the

;contd<

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1# C +RT# O6 RDR

receiver response that can !e tolerated

$eg the signal poer at hich the

receiver !egins to saturate%, and the

minimum signal might !e the minimum

detecta!le signal. The signalprocessor , hich is often in the I6

portion of the receiver, might !e

descri!ed as !eing the part of thereceiver that separates the desired signal

from the undesired

;contd<

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1# C +RT# O6 RDR

signals that can degrade the detectionprocess. #ignal processing includes the

matched filter that ma*imizes the

output to signal ' to ' noise ratio. #ignal

processing also includes the dopplerprocessing that ma*imizes the signal ' to

' clutter ratio of a moving target hen

clutter is larger than receiver noise, andit separates one moving target from other

;contd<

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1# C +RT# O6 RDR

moving targets or from clutter echoes.The detection decision is made at the

output of the receiver, so a target is

declared to !e present hen the receiver

output e*ceeds a predetermined threshold.If the threshold is set too lo, the receiver

noise can cause e*cessive false alarms. If

the threshold is set too high, detection ofsome targets might !e missed that ould

;contd<

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1# C +RT# O6 RDR

otherise have !een detected. Thecriterion for determining the level of the

decision threshold is to set the threshold

so it produces an accepta!le

predetermined average rate of false alarmsdue to receiver noise ' in militar" radars

ma" !e operator controlled.

fter the detection decision is made, thetrack of a target can !e determined, here

a track

;contd<

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1# C +RT# O6 RDR

is the locus of target locations measuredover time. This is an e*ample of data

processing . The processed data target

information might !e used to automaticall"

guide a missile to a target& or the radaroutput might !e further processed to

provide other information a!out the nature

of the target. The radar control insuresthat the various part of radar operate in a

coordinated and

;contd<

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1# C +RT# O6 RDR

cooperative manner, as eg providing timingsignals to various parts of the radar as

re)uired.

The radar engineer has as resources>

Time that allos good doppler

processing.

1andidth for good range resolution.

#pace that allos a large antenna.

;contd<

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1# C +RT# O6 RDR

-nerg" for long range processing

performance and accurate

measurements.

-*ternal factors affecting radar

performance include the>

Target characteristics .

;contd<

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1# C +RT# O6 RDR

-*ternal noise that might enter via the antenna.

Unanted Clutter echoes from land,

sea, !irds, or rain.

Interference from other electromagnetic radiators.

+ropagation effects due to the

earth0s surface and atmosphere.

These factors mentioned to emphasize that the" can !e highl"

important in the design and application of a radar.

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RDR TRN#8 TT-R#

The radar transmitter must not onl" !ea!le to generate the peak and average

poers re)uired to detect the desired

targets at the ma*imum range, !ut alsoto generate a signal ith a proper

aveform and the sta!ilit" needed for

the particular application. Transmitters

ma" !e oscillators or amplifiers, !ut the

later usuall" offer more advantages.

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RDR TRN#8 TT-R#

There have !een man" t"pes of radar poersources used in radar>

The 8agnetron poer oscillator as

at one time ver" popular, !ut it is

seldom used e*cept for civil marine radar. 1ecause of the magnetron0s

relativel" lo average poer $3 or ?

@A% and poor sta!ilit", other poer

sources are usuall" more appropriate for applications re)uiring long B range

detection of small moving targets in

$contd%

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RDR TRN#8 TT-R#

the presence of large clutter echoes. The magnetron poer oscillator is an

e*ample of hat is called a crossed '

field tu!e.

There is also a related crossed ' field

amplifier $C6% that has !een in some

radars in the past, !ut it also suffers

limitations for important radar applications, especiall" for those

re)uiring detection of moving targets

in clutter.

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RDR TRN#8 TT-R#

The high ' poer@l"stron

and the

travelling ave tu!e $TAT% are

e*amples of hat are called linear

!eam tu!es. t the high poers

often emplo"ed !" radars, !oth tu!es

have suita!l" ide !andidths as

ell as good sta!ilit" as needed for

doppler processing, and !oth have

!een popular.

The #olid ' state amplifier , such as

the transistor, has also !een used in

radar, especiall" in phased arra"s.

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RDR TRN#8 TT-R#

lthough an individual transistor has

relativel" lo poer, each of the

man" radiating elements of an arra"

antenna can utilize multiple

transistors to achieve the high poer

needed for man" applications.

Ahen solid ' state transistor

amplifiers are used, the radar

designer has to !e a!le to>

accommodate the high dut" c"cle at

hich these devices have to operate.

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RDR TRN#8 TT-R#

the long pulses the" must use that re)uire pulse compression.

the multiple pulses of different

idths to allo detection at short as ell as long range.

Thus the use of solid ' state

transmitters can have an effect

on other parts of the radar

s"stem.

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RDR TRN#8 TT-R#

t millimeter avelengths ver" high

poer can !e o!tained ith the

g"rotron , either as an oscillator or as

an amplifier.

The grid ' control vacuum tu!e as

used to good advantage for a long time

in U6 and lo fre)uenc" radars '

although less interest in the lo fre)uencies for radar ' hoever some

sa" chinese 6 radars $designed some

decades ago due to lack of technolog"

kno ho% can pick stealth aircraft.

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RDR TRN#8 TT-R#

lthough not ever" e*pert might agree, some radar

s"stem engineers ' if given

a choice ' ould consider

the @l"stron amplifier as

the prime candidate for a

high poer modern radar if

the application ere

suita!le for its use.

RADAR BLOC"

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DIAGRAM

RADAR BLOC" DIAGRAM

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RADAR BLOC" DIAGRAM

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RDR 19OC@ D ER8

to an intermediate fre)uenc" $I6% here itis amplified !" the I6 amplifier. The signal

!andidth of a superheterod"ne receiver

is determined !" the !andidth of its I6

stage. The I6 fre)uenc" might !e F5 or :58z hen the pulse idth is of the order

of 3 Gs $ith a 3B Gs pulse idth, the I6

!andidth ould !e a!out 3 8z%. The I6amplifier is designed as a 8atched 6ilter

that is one hich ma*imizes $contd%

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RDR 19OC@ D ER8

the peak ' signal ' to ' mean ' noise ratio.Thus the matched filter ma*imizes the

detecta!ilit" of eak echo signals and

attenuates unanted signals. Aith the

appro*imatel" rectangular pulse shapescommonl" used in man" radars,

conventional radar receiver filters are close

to that of a matched filter hen the receiver

!andidth 1 is the inverse of the pulse

idth τ , or 1 τ H 3.

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RDR 19OC@ D ER8

#ome times the lo ' noise input stage is omitted

and the mi*er !ecomes the first stage of the

receiver. receiver ith a mi*er as the input

stage ill !e less sensitive !ecause of the

mi*er0s higher noise figure& !ut it ill have

greater d"namic range, less suscepti!ilit" to

overload, and less vulnera!ilit" to electronic

interference than a receiver ith a lo ' noise

first stage. These attri!utes of a mi*er stage

might !e of interest for militar" radars su!(ect tothe nois" environment of hostile electronic

countermeasures $-C8%.

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RDR 19OC@ D ER8

The I6 amplifier is folloed !" a cr"stal

diode, hich is traditionall" called the

second detector or demodulator . Its

purpose is to assist in e*tracting the signal

modulation from the carrier. Thecom!ination of I6 amplifier, second detector

and video amplifier act as an envelope

detector to pass the pulse modulation

$envelope% and re(ect the carrier fre)uenc". $contd%

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RDR 19OC@ D ER8

In radars that detect the doppler shift of the

echo signal, the envelope detector is replaced

!" a phase detector , hich is different from

the envelope detector shon in the !lock

diagram $slide :%. The com!ination of I6amplifier and video amplifier is designed to

provide sufficient amplification, or gain, to

raise the level of the input signal to a

magnitude here it can !e seen on a displa",such as a cathode ' ra" tu!e $CRT%, or !e the

input signal to a digital computer for further

processing.

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RDR 19OC@ D ER8

t the output of the receiver a decisionis made hether or not a target is

present. The decision is !ased on the

magnitude of the receiver output. If

the output is large enough to e*ceed a

pre ' determined threshold, the

decision is that a target is present. If

it does not cross the threshold, onl"noise is assumed to !e present.$contd%

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RDR 19OC@ D ER8

The threshold level is set so that therate at hich false alarms occur due to

noise crossing the threshold $in the

a!sence of signal% is !elo some

specified, tolera!le value. This is fine

if the noise remains constant, as hen

receiver0s on noise dominates. If, on

the other hand, the noise is e*ternal tothe radar $as from unintentional == $contd%

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RDR 19OC@ D ER8

=. interference or from deli!eratenoise (amming% or if clutter echoes

$from the natural environment% are

larger than the receiver noise, thethreshold has to !e varied adaptivel"

in order to maintain the false alarm

rate at a constant value. This isaccomplished !" a constant false

alarm rate $C6R% receiver.

RADAR BLOC" DIAGRAM

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RADAR BLOC" DIAGRAM

RADAR BLOC" DIAGRAM

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RADAR BLOC" DIAGRAM

RADAR $RE(UENCIES

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RADAR $RE(UENCIES

RADAR LETTER DESIGNATIONS

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RADAR $UNCTIONS

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% Norma6 ra;ar f)nction&''/ ra#2 0)ro5 p+4" d4a-3/ ;4o1!- 0)ro5 Dopp4r )r*+#- "$1)!3%/ a#2+4ar d1r!1o# 0)ro5 a#!##a po1#!1#23

% Signat)re ana6<&i& an; inver&e&cattering'

/ !ar2! "1( 0)ro5 5a2#1!+d o) r!+r#3>/ !ar2! "$ap a#d o5po##!" 0r!+r# a" a

)+#!1o# o)

d1r!1o#3/ 5o;1#2 par!" 05od+4a!1o# o) !$ r!+r#3K/ 5a!r1a4 o5po"1!1o#

RADAR $UNCTIONS

APPLICATION O$ RADARS

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IN$ORMATION A+AILABLE $ROM RADARS

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N6O 919- > RDR

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ngular Direction

One method to determine direction to target is determine here magnitude

of echo signal is ma*imum.

Re)uires antenna ith a narro !eamidth $a high gain antenna%.

ngle to target in one angular

dimension can !e determined !" using

to antennas, displaced in angle, and

comparing the echo amplitude

received in each !eam. $contd%

N6O 919- > RDR

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ngular Direction

6our !eams needed to o!tain angle measurement in !oth azimuth and

elevation.

8onopulse tracking radar uses this principle.

ccurac" of angle measurement

depends on electrical size of the antenna& ' the size of antenna given

in avelengths.

N6O 919- > RDR

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#ize and #hape

If radar has sufficient resolution

capa!ilit" in range or angle, can

provide measurement of target e*tent.

Range is usuall" the coBordinate here resolution is o!tained.

Resolution in cross ' range $given !"

range multiplied !" antenna

!eamidth% can !e o!tained ith ver"

narro !eamidth antennas.

$contd%

N6O 919- > RDR

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#ize and #hape

ngular idth of an antenna !eam is limited, so cross ' range

resolution o!tained !" this method

not as good as range resolution.

er" good resolution in the cross

range dimension o!tained !"

emplo"ing doppler fre)uenc" domain, !ased on #R or I#R.

$contd%

N6O 919- > RDR

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#ize and #hape

Need of relative motion !eteen the target and the radar to o!tain cross '

range resolution !" #R or I#R.

Aith sufficient resolution in !oth

range and cross ' range, not onl" can

size !e o!tained in to orthogonal coB ordinates, !ut target shape can

sometimes !e discerned.


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N6O 919- > RDR

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Doppler

nother application of doppler shift ' o!servation of eather '

Ne*rad radars of U#.

#R and I#R are also !ased on

doppler fer)uenc" shift.

ir!orne doppler navigation radar

also !ased on doppler shift.

N6O 919- > RDR

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Doppler

Use of doppler in radar places greater demands on sta!ilit" of

radar transmitter .

Increases comple*it" of signal

processing. Re)uirements accepted to achieve

significant !enefits offered !"

doppler.

Doppler shift ke" capa!ilit" of radar B

can measure speed ' traffic police,

other velocit" measuring applications.

E$$ECT O$ OPERATING $RE(ON RADAR

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ON RADAR

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-66-CT O6 O+-RT NE 6R-2 > RDR

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6 ' F to F5 8z

8a(or use of 6 !and is to detect targets at long ranges $out to ?555

nmi% !" taking advantage of refraction

of 6 energ" !" ionosphere.

Radio amateurs refer it as short ' ave propagation ' communicate over long

distances.

Targets for such 6 radars might !e

aircraft, ships and !allistic missiles.

lso echo from sea surface provide

information a!out direction and speed

of inds that drive the sea


6 ' F5 to F55 8z

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Radar development in 34F5s !egan in

this !and as these fre)uencies

represented frontier of radio technolog".

Eood fre)uenc" for long range air

surveillance or detection of !allistic

missiles. t 6 reflection coefficient on scattering

from earth0s surface can !e ver" large $over

ater% ' constructive interference !eteen

direct signal and surface reflected signal can

increase significantl" range of 6 radar ' can dou!le radar0s range.

Destructive interference decreases range due

to deep nulls in antenna pattern in elevation

plane.


6 ' F5 to F55 8z

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Destructive interference can result in poor

lo ' altitude coverage. Detection of moving targets in clutter !etter at

loer fre)uencies hen radar takes advantage of

doppler fre)uenc" shift !ecause doppler

am!iguities $that cause !lind speeds% are feer at lo fre)uencies.

6 radars not !othered !" echoes from rain

!ut can !e affected !" multiple ' time around

echoes from meteor ionization and aurora.

RC# of aircraft at 6 is generall" larger than RC# at higher fre)uencies ' radar e)uation.

6 radars cost less compared to radars ith

the same range performance that operate at

higher fre)uencies.


6 ' F5 to F55 8z

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8an" attractive advantages !ut

serious limitations too.

Deep nulls J poor lo altitude cover.

vaila!le spectral idths assigned are

small so range resolution poor.

ntenna !eamidths are usuall"

ider than at microave fre)uencies so poor resolution and accurac" in

angle.

6 !and crodedB civilian T, 68, ..


6 ' F5 to F55 8z

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-*ternal noise levels entering radar

via antenna higher at 6 visBKBvis

microave fre)uencies.

Chief limitation o!taining spectrum

space at these croded fre)uencies. 6 surveillance radar idel" used !"

#oviet Union ' large countr", loer cost

made attractive for air surveillance of

large e*panse of countr" ' produced large num!ers, large size, long range.

6 air!orne intercept radars used !"

Eermans AABII. #NB? air!orne, :5B355

Radars at 6 not affected !" Chaff


U6 ' F5 to 3555 8z

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8an" characteristics of radar operating in 6 region appl" to U6.

U6 is good fre)uenc" for ir!orne

8oving Target Indication $8TI% radar

in ir!orne -arl" Aarning Radar$-A%. Eood fre)uenc" for operation of long

range radars B detection and tracking

of satellites and !allistic missiles.

t upper portion !and long range

ship!oard air ' surveillance radars and

radars $called ind profilers % ' measure

speed and direction of ind


U6 ' F5 to 3555 8z

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Eround +enetrating Radar $E+R% e*ample of

Ultraide!and $UA1% radar. Aide signal !andidth

covers !oth 6 and U6 !ands ' L5 to L55 8z.

Aide signal 1A needed to o!tain good

range resolution.

9oer fre)uencies needed to allo the

propagation of radar energ" into ground.

-ven than loss in propagating through

through t"pical soil high ' range of

simple mo!ile E+R onl" fe meters. Ranges suita!le for locating !uried lines

and pipe lines as ell as !uried o!(ects.

Radar to see targets located on surface !ut

ithin foliage re)uire same fre)uencies as E+R.


9 1and ' 3 to ?.5 Ez

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+referred fre)uenc" !and for operation of longBrange $to ?55 nmi%

air ' surveillance radars.

ir Route #urveillance Radar $R#R%

for long range airBtraffic control is eg.

s fre)uenc" increases effect of rain

on performance !ecomes significant '

radar designer has to orr" a!out reducing effect of rain at 9 !and.

6re)uenc" !and attractive for long

range detection satellites and IC18s


# 1and ' ?.5 to M.5 Ez

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irport #urveillance Radar $#R% that monitors air traffic ithin the region

of an airport at # 1and. Range

t"picall" L5 to :5 nmi. FD radar that

determines range, azimuth angle, and elevation angle achieved at # !and.

-arlier ' long range surveillance !etter

at lo fre)uencies and accurate

measurement target location !etter at

high fre)uencies ' if single radar

operating at single fre)uenc" !and used

then # !and good compromise


# 1and ' ?.5 to M.5 Ez

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#ometimes accepta!le to use C !and

as choice for radar that performs !oth

functions.

AC# air!orne air ' surveillance radar operates at # !and ' usuall"

most radar applications are !est

operated in a particular fre)uenc" !and at hich the radar0s performance

is optimum.


# 1and ' ?.5 to M.5 Ez

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oever e*ample of AC# air!orne air

' surveillance at # !and vs U# Nav" -?

-A radar at U6 ' inspite of such

difference in fre)uenc" !oth radars have

compara!le performance ' e*ception to

o!servation a!out an optimum fre)uenc"

!and for each application.

Ne*rad eather radar operates at #

!and. Eood fre)uenc" for o!servation of eather !ecause loer fre)uenc" ould

produce much eaker radar echo signal

from rain ' radar echo from rain varies as

fourth poer of fre)uenc".


# 1and ' ?.5 to M.5 Ez

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higher fre)uenc" ould produce attenuation of the signal as it propagates

through the rain and ould not allo an

accurate measurement of rainfall rate.

There are eather radars at higher

fre)uencies !ut usuall" of shorter range

than Ne*rad and could !e used for more

specific eather radar application than accurate meteorological measurements

provided !" Ne*rad.


C 1and ' M.5 to I.5 Ez

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1and lies !eteen # and !ands and

has properties in !eteen the to.

Often either # or !and might !e

preferred to the use of C !and ' although man" applications in past for

C !and. This !and also used !"

satellite communication ' ma"!e radar application not first choice.


1and ' I.5 to 3?.5 Ez

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Relativel" popular radar !and for militar" applications. Aidel" used in militar" air!orne

radars for performing the roles of interceptor,

fighter and attack of ground targets.

lso popular for imaging radars !ased on #R and I#R.

!and suita!le fre)uenc" for civil marine

radars, air!orne eather avoidance radar,

air!orne doppler navigation radars and police

speed meter.

8issile guidance s"stems are also at !and.


1and ' I.5 to 3?.5 Ez

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Radars at !and are generall" of

convenient size and of interest here

mo!ilit" and light eight are important

and ver" long range is not a ma(or

re)uirement.

Relativel" ide range of fre)uencies

availa!le at !and and a!ilit" to o!tain

narro !eamidths ith relativel" small

antennas in this !and important

considerations for high ' resolution

applications.

igh fre)uenc" of !and serious factor

in reducing performance ith rain.


, K , 1ands ' 3?.5 to M5 Ez

K U K a

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6or higher radar fre)uenc" ph"sical size of antennas decrease ' generall" more

difficult to generate large transmit pr.

Range performance of radars at fre)uencies a!ove !and is generall"

less than that of !and.

8ilitar" air!orne radars are found at

!and as ell as !and.

6re)uenc" !ands attractive hen radar

of smaller size not re)uiring long range.

K U


, K , 1ands ' 3?.5 to M5 Ez

K U K a

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irport #urface Detection -)uipment

$#D-% found on top of control toer at

ma(or airports at !and primaril"

!ecause of !etter resolution than !and.

Original @ !and has ater ' a!sorption line at ??.? Ez ' causes attenuation can

!e serious pro!lem in some applications.

Discovered after development of @ '

!and radars during AABII. #o and

!ands ere later introduced.

Radar echo from rain can limit capa!ilit"

of radars at these fre)uencies

K U

K U K

a


8illimeter Aave Radar

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8ost interest in millimeter ave radar has

!een in vicinit" of 4M Ez ' there is a minimum called indo in atmospheric

attenuation.

Aindo is a region of lo attenuation

relative to ad(acent fre)uencies ' indo at 4M Ez is a!out as ide as the entire

microave spectrum.

6or radar millimeter ave region starts at

M5 Ez or higher ' technolog" of millimeter ave radars and propagation effects of

environment not onl" different from

microave radars !ut usuall" much more

restricting .

RDIO AINDOA

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Unlike e*perience at microaves

millimeter radar signal can !e highl"

attenuated even hen propagating in

clear atmosphere ' attenuation varies

over millimeter ave region. ttenuation at 4M Ez indo is higher

than attenuation of atmospheric ater '

vapour a!sorption line at ??.? Ez. One ' a" attenuation in o*"gen

a!sorption line at :5 Ez is a!out 3? d1

per @m hich precludes its application



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ttenuation in rain can also !e a

limitation in the millimeter ave

region.

Interest in millimeter ave radar primaril" !ecause of challenges as

frontier to !e e*plored and put to

productive use.

Eood features are great place for

emplo"ing ide 1A signals ' plent" of

spectrum space availa!le.



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Radars can have high range ' resolution and

narro !eamidths ith small antennas. ostile countermeasures to militar" radars

are difficult to emplo".

-asier to have a militar" radar ith lo

pro!a!ilit" of intercept at these fre)uencies

than at loer fre)uencies.

8illimeter ave transmitters not capa!le of

average poer more than fe hundred atts $even less% ' advances in g"rotrons can

produce average poer man" times more than

conventional millimeter ave poer sources '

availa!ilit" of high poer not a limitation no.


9aser Radar

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9asers can produce usa!le poer at optical

fre)uencies and in the infrared region of the spectrum.

Can utilize ide 1A $ver" short pulses% and can

have ver" narro !eamidths.

ntenna apertures much smaller than

microaves.

ttenuation in atmosphere and rain ver" high '

performance in !ad eather )uite limited.

Receiver noise determined !" )uantum effects

rather than thermal noise.

#everal reasons ' laser radar limited

application

RADAR E(UATION

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RADAR E(UATION

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INTEGRATION O$ RADAR PULSES

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RADAR CROSS SECTION O$ TARGETS

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RADAR CROSS SECTION$LUCTUATIONS

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RADAR CROSS SECTION $LUCTUATIONS

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TRANSMITTER POWER

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ANTENNA PARAMETERS

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ANTENNA PARAMETERS * BEAMS

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S#STEM LOSSES

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ANTENNA LOSSES dB

SIGNAL PROCESSING LOSSES dB

DOPPLER PROCESSING RADARS

LOSSES /% dB COLLAPSING LOSSES '/ dB

OPERATOR LOSSES

EUIPMENT DEGRADATION '?% dB PROPAGATION EFFECTS

S#STEM LOSSES

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RADAR E(UATION RE+ISED

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DOPPLER AND MTI RADAR

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D-9 ' 9 N- CNC-9-R#

#imple 8TI dela" ' line canceller $D9C% seen

li i ti d i filt th t ( t

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earlier is a time ' domain filter that re(ects stationar" clutter at zero fre)uenc". It has a

fre)uenc" response function $f % that can !e

derived from time ' domain representation of

signals. Can !e ritten as>

$f % P ? #in $ %

8agnitude sketched as>

f dT pπ

)f (H

D-9 ' 9 N- CNC-9-R#

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D-9 ' 9 N- CNC-9-R#

1lind #peeds

Th f th i l d l li

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The response of the single dela" ' linecanceller ill !e zero henever the

magnitude of

#in $ % P 5

Ahich occurs hen !racket term is P 5,

± π, Q ?π, Q Fπ …..

π f d T p

D-9 ' 9 N- CNC-9-R#

1lind #peeds

$In addition to zero response at zero

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In addition to zero response at zero fre)uenc" there ill also !e zero

response of dela" ' line canceller

henever the doppler fre)uenc" is a

multiple of the pulse repetition fre)uenc".

$ The radial velocities that produce !lind speeds

can !e evolved from the e)uations.

$ Onl" the first !lind speed is considered since

the others are its integer multiples.$ plot of the first !lind speed as a function of

pulse repetition fre)uenc" and radar fre)uenc"

!ands is as shon.

19 ND #+--D#

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19 ND #+--D#

1lind speeds can !e a serious

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1lind speeds can !e a serious limitation in 8TI radars since the"

cause desired moving targets to !e

cancelled ith undesired clutter at

zero fre)uenc".

6our methods for reducing detrimental

effects of !lind speeds.

19 ND #+--D#

Operate the radar at long avelengths

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Operate the radar at long avelengths $lo fre)uencies%.

Operate ith a high pulse repetition

fre)uenc". Operate ith more than one pulse

repetition fre)uenc".

Operate ith more than one R6 fre)uenc" $ avelength%.

19 ND #+--D#

Com!inations of to or more of the

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Com!inations of to or more of thea!ove are also possi!le to further

alleviate the effect of !lind speeds.

-ach of these four methods has

particular advantages as ell as

limitations, so there is not ala"s a

clear choice as to hich to use in an"

particular application.

19 ND #+--D#

9o R6 fre)uenc" chosen to avoid

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9o R6 fre)uenc" ' chosen to avoid !lind speed ' first !lind speed ' :M5 @t

$appro* 8ach 3% ' +R6 ' FF5 z

$unam!iguous range ' ?ML nmi% ' than

radar 2 P ? m ' corresponds to f P 3L5

8z $6 region%.

8an" radars !uilt ' still has

advantages ' not desira!le for long

range air B surveillance ' man"

reasons.

19 ND #+--D#

Resolution in range and angle poor

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Resolution in range and angle poor due to narro 1As and large

!eamidths.

+ortion of -8 spectrum croded ' 68,

T.

9o ' altitude coverage generall" poor

Thus attempting to use lo fre)uenciesto avoid !lind speed pro!lem not

usuall" a desira!le option for radar.

19 ND #+--D#

Operate at high R6 fre)uenc" and

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Operate at high R6 fre)uenc" and increase +R6 to avoid !lind speeds '

have to tolerate man" range

am!iguities ' if first !lind speed :M5

@t and 2 P 5.3 m $# !and fre)uenc" of

F555 8z% ' +R6 P ::55 z.

Results in ma* unam!iguous range of 3?.F nmi ' small for man" radar

applications ' ma"!e for pulse doppler.

19 ND #+--D#

Ahen to or more +R6s used in radar !lindd t +R6 diff t f !li d d

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Ahen to or more +R6s used in radar ' !lind speeds at one +R6 different from !lind speeds

at other +R6s.

Targets that are highl" attenuated ith one

+R6 might !e readil" seen ith another +R6. Techni)ue used ith air ' surveillance '

especiall" for civil air traffic control.

Disadvantage of multiple ' +R6 aveform is multiple ' time ' around clutter echoes $from

regions !e"ond the ma*imum unam!iguous

range% are not cancelled.

19 ND #+--D#

Radar that can operate at to or more R6 fre)uencies

can also unmask !lind speeds.

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Re)uired fre)uenc" change often larger than might !e

possi!le ithin the usual fre)uenc" !ands allocated for

radar use.

limitation of multiple fre)uencies is need for greater

s"stem !andidth.

8ight !e desira!le to tolerate !lind speeds rather than

accept limitations of methods descri!ed.

s in man" aspects of -ngineering no one single solution !est for all cases.

-ngineer has to decide hich a!ove limitations can !e

accepted in an" particular application.

19 ND #+--D#

1lind speeds occur !ecause of the

sampled nature of the pulse radar

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sampled nature of the pulse radar aveform.

Thus it is sampling that is cause of

am!iguities, or aliasing, in the measurement of the doppler fre)uenc"

' (ust as sampling in a pulse radar $at

the +R6% can give rise to am!iguities in the range measurement.

C9UTT-R TT-NUT ON

Other limitation of single dela" ' line

canceller is insufficient attenuation of

clutter that results from finite idth of

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clutter that results from finite idth of clutter spectrum.

#ingle dela" ' line canceller hose

fre)uenc" response shon in slide ?LM does hat supposed to do ' cancel

stationar" clutter ith zero doppler

shift. Real orld hoever clutter spectrum

has finite idth due to>

C9UTT-R TT-NUT ON

Internal motion of the clutter.

Insta!ilities of the stalo and cohoill t

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Insta!ilities of the stalo and coho oscillators.

Other imperfections of the radar and

its signal processor. 6inite signal duration.

6actors that iden clutter spectrum

are comple* ' clutter poer spectral densit" represented !" gaussian

function.

C9UTT-R TT-NUT ON

Conse)uences of a finite ' idth

clutter spectrum can !e seen from

figure $slide ?75%

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figure $slide ?75%. 6re)uenc" response of single dela" '

line canceller shon !" the solid

curve encompasses a portion of the clutter spectrum ' therefore clutter

ill appear in the output ' greater the

standard deviation, greater the

amount of clutter that ill !e passed

!" the filter to interfer ith moving

target indication.

C9UTT-R TT-NUT ON

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C9UTT-R TT-NUT ON

If a second dela" ' line canceller is

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If a second dela" ' line canceller is placed in cascade, the fre)uenc"

response of to filters is the s)uare of

the of the single dela" ' line canceller

$f% P M #in? $ %

This is indicated !" dashed curve in 6ig

π

f d T p

C9UTT-R TT-NUT ON

9ess of the clutter spectrum is

included ithin the fre)uenc"

response of the dou!le dela" ' line

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response of the dou!le dela" ' line canceller.

Thus it attenuates more of the clutter.

Clutter ttenuation $C% for the dou!le dela" ' line canceller is>

C P P

σ π 44

48

4

c

f p

σ π

λ

44768

44

v

f p

C9UTT-R TT-NUT ON

dditional dela" ' line cancellers can

!e cascaded to o!tain a fre)uenc"

response $f% hich is the nth

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response $f% hich is the n th

poer of the single dela" ' line

canceller given !" e)uation of slide

?LF, here n is the num!er of dela" '

line cancellers.

8T 8+RO-8-NT 6CTOR

C is a useful measure of the

performance of an 8TI radar in

cancelling clutter ' !ut has inherent

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cancelling clutter ' !ut has inherent eaknesses.

C can !e made infinite !" turning off

the radar receiver ' this cannot !e done since it also eliminates the

desired moving ' target echo signals.

The I--- defined a measure of performance knon as 8TI

Improvement 6actor .

8T 8+RO-8-NT 6CTOR

8TI improvement factor includes the

signal gain as ell as the clutter

attenuation

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attenuation.

Defined as The signal ' to ' clutter

ratio at the output of the clutter filter

divided !" the signal ' to ' clutter ratio

at the input of the clutter filter,

averaged uniforml" over all target radial velocities of interest.

8T 8+RO-8-NT 6CTOR

-*pressed as>

I t 6 t I

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Improvement 6actor P If P

P C average gain

8T 8+RO-8-NT 6CTOR

ertical line on right of a!ove

e)uation indicates that average is

taken ith respect to doppler

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taken ith respect to doppler

fre)uenc" f d .

Improvement factor can !e e*pressed as the clutter attenuation

C P 0Cin = Co)t4 times the

average filter gain

8T 8+RO-8-NT 6CTOR

The average gain is determined from

the filter response $f% and is usuall"

small compared to clutter attenuation

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small compared to clutter attenuation.

verage gain for a single dela" ' line

canceller is ? and for a dou!le dela" '

line canceller is :.

8T 8+RO-8-NT 6CTOR

The improvement factors for single

and dou!le dela" ' line cancellers are>

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8T 8+RO-8-NT 6CTOR

The general e*pression for the

improvement factors for a canceller

ith n dela" line cancellers in

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ith n B dela" ' line cancellers in

cascade is>

+U9#- DO++9-R

++9 CT ON#

J R-2U R-8-NT#

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CO8+R #ON O6 8T J +U9#-

DO++9-R RDR# 6OR RBtoB

R

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radar fall2015 (3)

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