radar block

8/9/2019 Radar Block

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A Basic Pulse RadarA Basic Pulse Radar


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The Basic Radar ComponentsThe Basic Radar Components

1.1. Power Supply:Power Supply:

Power is initiallyPower is initiallyprovided from theprovided from thenormal mains (!"normal mains (!"

#!$% or 11#" &!$%'.#!$% or 11#" &!$%'... A radar set re)uiresA radar set re)uires

differin* levels anddifferin* levels andforms of supply+forms of supply+ e.g.e.g.

1,!"+ ,!!$% or 11#"+1,!"+ ,!!$% or 11#"+!!$%+ provided -y!!$%+ provided -yassociated conversionassociated conversionmachinery.machinery.


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. Transmitter. Transmitteresi*ned to produceesi*ned to produce

pulses of electroma*neticpulses of electroma*neticener*y of a fi/ed durationener*y of a fi/ed duration( Pulse uration' at( Pulse uration' atre*ular intervals (PR0re*ular intervals (PR0Pulse RepetitionPulse Repetition0re)uency'.0re)uency'.

These pulses ideally mustThese pulses ideally must-e of s)uare shape so-e of s)uare shape sothat the leadin* ed*esthat the leadin* ed*esare clearly defined forare clearly defined forran*in* purposes. Theran*in* purposes. The

pulses *enerally are of apulses *enerally are of a*iven power at a fi/ed*iven power at a fi/edfre)uency+ and arefre)uency+ and areproduced as follows:produced as follows:


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a: Tri**era: Tri**erA.C. is fed to the tri**er unitA.C. is fed to the tri**er unit

(Synchroni%er+ or timer' which(Synchroni%er+ or timer' whichconverts the a.c. into a seriesconverts the a.c. into a seriesof short sharp pulses+ lowof short sharp pulses+ lowpowered+ -ut at correct prf.powered+ -ut at correct prf.

The tri**er unit ensures:The tri**er unit ensures:

2 That all circuits in the radarThat all circuits in the radaroperate in a definite timedoperate in a definite timedrelationship.relationship.

2 Times the interval -etweenTimes the interval -etweentransmitted pulses to ensure thattransmitted pulses to ensure thatthe interval is of proper len*th.the interval is of proper len*th.

The correct prf is set -y any sta-leThe correct prf is set -y any sta-leor -loc3in* oscillator.or -loc3in* oscillator.

Then pulse shapin* circuitsThen pulse shapin* circuits

produce timin* pulses.produce timin* pulses.


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-: 4odulator-: 4odulator

At the same time 4odulator isAt the same time 4odulator is

receivin* (from power supply'receivin* (from power supply'and storin* considera-leand storin* considera-leamount of ener*y.amount of ener*y.

The 4odulator is tri**ered -yThe 4odulator is tri**ered -ythe pulses from the Tri**erthe pulses from the Tri**er

and releases ener*y in theand releases ener*y in theform of hi*h tension (ht' pulsesform of hi*h tension (ht' pulseswhich are passed to thewhich are passed to the5scillator'.5scillator'.

64odulator volta*e may -e as64odulator volta*e may -e ashi*h as 1!!+!!! " in hphi*h as 1!!+!!! " in hp

transmitters+ so e/treme caretransmitters+ so e/treme careis essential while handlin*is essential while handlin*such parts of the radar78such parts of the radar78


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c: 5scillatorc: 5scillatorThe 4odulator pulse is applied toThe 4odulator pulse is applied to

the cathode of the oscillator (whichthe cathode of the oscillator (whichcould -e a 9lystron+ or 4a*netron '.could -e a 9lystron+ or 4a*netron '.

The 5scillator -ursts intoThe 5scillator -ursts intooscillations while -ein* suppliedoscillations while -ein* suppliedwith ht pulses+ producin* pulses ofwith ht pulses+ producin* pulses ofem ener*y at the re)uiredem ener*y at the re)uired

fre)uency.fre)uency.

hen the 4odulator is dischar*ed+hen the 4odulator is dischar*ed+the ht pulses cease+ as does thethe ht pulses cease+ as does theoscillation+ and the transmitter isoscillation+ and the transmitter is)uietest until the tri**er unit)uietest until the tri**er unit

produces the ne/t pulse when theproduces the ne/t pulse when thecycle is repeated7cycle is repeated7


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To emphasi%e the time scale of this process+ if the pulseTo emphasi%e the time scale of this process+ if the pulseduration is usec+ and the PR0 is #!! every second+duration is usec+ and the PR0 is #!! every second+

then the ht is provided to the oscillator for a period ofthen the ht is provided to the oscillator for a period ofusec every !!!usec+ the oscillator -ein* switched offusec every !!!usec+ the oscillator -ein* switched offfor 1;;,usec.for 1;;,usec.

The 5scillator is the power output sta*e of theThe 5scillator is the power output sta*e of the

transmitter passin* radio fre)uency pulses to the aerial.transmitter passin* radio fre)uency pulses to the aerial.The radar displays must -e synchroni%ed with the pulseThe radar displays must -e synchroni%ed with the pulsetransmissions so it is necessary for the synchroni%in*transmissions so it is necessary for the synchroni%in*pulses to -e fed from the transmitter.pulses to -e fed from the transmitter.

The synch. pulse starts the spot movin* on the displayThe synch. pulse starts the spot movin* on the display

at the same instant at which the R0 pulse -e*ins to -eat the same instant at which the R0 pulse -e*ins to -etransmitted from the aerial.transmitted from the aerial.


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i3e other units+ aerial desi*nvaries in detail from set to setvaries in detail from set to setdependin* upon the purpose anddependin* upon the purpose andfre)uency of transmissions.fre)uency of transmissions.

Ideally, the Oscillator should

be situated close to aerial, to

cut down power losses, but

This is not always possible.So the most efficient method

Of transferring the energy

from the oscillator to the

aerial must be used


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0or >ow 0re)uency metric Radars+ it is0or >ow 0re)uency metric Radars+ it is

possi-le to use a special ca-le or feederpossi-le to use a special ca-le or feeder

(coa/ial' as transmission line+ -ut(coa/ial' as transmission line+ -ut

At $i*her fre)uencies ave*uides areAt $i*her fre)uencies ave*uides are

used.used.

ave*uides are carefully desi*nedave*uides are carefully desi*ned

trun3in* + which *uide the waves fromtrun3in* + which *uide the waves from

oscillator to the aerial.oscillator to the aerial.


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Switchin* the antenna -etween the transmit andSwitchin* the antenna -etween the transmit andreceive modes presents one pro-lem?receive modes presents one pro-lem?

ensurin* that ma/imum use is made of theensurin* that ma/imum use is made of theavaila-le ener*y is another.availa-le ener*y is another.

The simplest solution is to use a switch toThe simplest solution is to use a switch totransfer the antenna connection from thetransfer the antenna connection from thereceiver to the transmitter durin* the transmittedreceiver to the transmitter durin* the transmittedpulse and -ac3 to the receiver durin* the echopulse and -ac3 to the receiver durin* the echopulse.pulse.

@o practical mechanical switches are availa-le@o practical mechanical switches are availa-lethat can open and close in a few microseconds.that can open and close in a few microseconds.Therefore+ electronic switches must -e used.Therefore+ electronic switches must -e used.


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uple/ers are constructed in many forms+ such asuple/ers are constructed in many forms+ such as2 hy-ridrin* duple/er+ orhy-ridrin* duple/er+ or

2 resonant cavity coa/ial or wave*uide systems+resonant cavity coa/ial or wave*uide systems+with TR and ATR tu-es+with TR and ATR tu-es+

or withor with pin diodespin diodes

ave*uide and hy-ridrin* duple/ers are most commonave*uide and hy-ridrin* duple/ers are most commonin radar systems.in radar systems.

The simplest solution would -e here to use aThe simplest solution would -e here to use aferrite circulatorferrite circulator. $owever+ it is complicated to ma3e. $owever+ it is complicated to ma3ecirculators for top performances up to many 1!! 3 incirculators for top performances up to many 1!! 3 inthe practice. =n addition+ circulators have a decouplin* ofthe practice. =n addition+ circulators have a decouplin* ofhardly more as
http://www.radartutorial.eu/21.semiconductors/hl14.en.htmlhttp://www.radartutorial.eu/21.semiconductors/hl14.en.htmlhttp://www.radartutorial.eu/17.bauteile/bt33.en.htmlhttp://www.radartutorial.eu/17.bauteile/bt33.en.htmlhttp://www.radartutorial.eu/17.bauteile/bt33.en.htmlhttp://www.radartutorial.eu/21.semiconductors/hl14.en.html


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errite !irculatorserrite !irculators

0errite circulators are often used0errite circulators are often usedas a duple/er+ *enerally inas a duple/er+ *enerally inmodules for active antennae.modules for active antennae.

The operation of a circulator canThe operation of a circulator can-e compared to a revolvin* door-e compared to a revolvin* doorwith three entrances and onewith three entrances and onemandatory rotatin* sense.mandatory rotatin* sense.

This rotation is -ased on theThis rotation is -ased on theinteraction of theinteraction of theelectroma*netic wave withelectroma*netic wave with

ma*netised ferrite.ma*netised ferrite.A microwave si*nal enterin* viaA microwave si*nal enterin* viaone specific entrance followsone specific entrance followsthe prescri-ed rotatin* sensethe prescri-ed rotatin* senseand has to leave the circulatorand has to leave the circulatorvia the ne/t e/it.via the ne/t e/it.

ner*y from the transmitterner*y from the transmitterrotates anticloc3wise to therotates anticloc3wise to theantenna port. "irtually allantenna port. "irtually allcirculators used in radarcirculators used in radarapplications contain ferrite.applications contain ferrite.

At first in 0errite circulators the

ener*y divides into two e)ual parts at

the entrance (1'+ -ut these parts *et

a different propa*ation speed -y the

influence of the ferrite.At the connection "-oth si*nal

parts are on in opposition+ they well

e/tin*uish themselves.

Both si*nal parts are in#phaseat the

connection $+ they add themselves

up to the complete si*nal power.


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By the symetric construction of the ferriteBy the symetric construction of the ferrite

circulator it is possi-le always tocirculator it is possi-le always to

determine a defined way direction -y thedetermine a defined way direction -y thechoice of the connection. =f an antenna ischoice of the connection. =f an antenna is

in a connection+ transmittin* ener*y isin a connection+ transmittin* ener*y is

always escorted to the antenna while thealways escorted to the antenna while theecho si*nals always find the way to theecho si*nals always find the way to the

receiver without influencin* one another7receiver without influencin* one another7


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Receiver =nput Receiver =nputTheThe echoechofed into the receiver via the TR Switchfed into the receiver via the TR Switch

isis minuteminutein terms of power. This is -ecause thein terms of power. This is -ecause thetransmitted pulse is dissipated as it radiates outtransmitted pulse is dissipated as it radiates outwards. The *reater the ran*e of the tar*et thewards. The *reater the ran*e of the tar*et theless the ener*y intercepted -y the tar*et.less the ener*y intercepted -y the tar*et.

The echo pulse reflected -y the tar*et li3ewiseThe echo pulse reflected -y the tar*et li3ewisespreads out on its return trip to aerial.spreads out on its return trip to aerial.

The main function of the receiver is to amplify orThe main function of the receiver is to amplify orincrease the stren*th of these tiny echo pulsesincrease the stren*th of these tiny echo pulsesso that they may -e seen and identified asso that they may -e seen and identified as

echoes on a display. The desi*n andechoes on a display. The desi*n andmaintenance of the receivers is most importantmaintenance of the receivers is most importanthowever+ -ecause electronic units ma3e theirhowever+ -ecause electronic units ma3e theirown electronicown electronic noisenoise..


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To avoid swampin* the tiny echoTo avoid swampin* the tiny echopulses with the internal noise+pulses with the internal noise+receiver circuits must havereceiver circuits must have lowlownoise characteristics.noise characteristics.

An AScanD with this noise+ orAn AScanD with this noise+ or*rassD is shown.EE*rassD is shown.EE

The Tar*et echo here is muchThe Tar*et echo here is muchpronounced than noise and can -epronounced than noise and can -eclearly seen+ -ut tar*et echo mayclearly seen+ -ut tar*et echo may-e too wee3 to -e mar*inally-e too wee3 to -e mar*inally

*reater than the noise and could*reater than the noise and couldnot -e seen.not -e seen.

The relation -etween the echo andThe relation -etween the echo andnoise is 3nown asnoise is 3nown as Si*nal to @oiseSi*nal to @oiseRatioRatio+ and *reater this ratio+ more+ and *reater this ratio+ moreefficient the receiver.efficient the receiver.

Fnwanted si*nals which includeFnwanted si*nals which includee/ternal noisee/ternal noisemay also o-scuremay also o-scurethe very small tar*et echoes.the very small tar*et echoes.

Remem-er+ the Receiver amplifiesRemem-er+ the Receiver amplifiesall inputs re*ardless of source.all inputs re*ardless of source.


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a 4i/in*a 4i/in*

Another complicationAnother complication

in *eneral receiverin *eneral receiverdesi*n is that it is notdesi*n is that it is not

easy electronically toeasy electronically to

amplify si*nals at R0+amplify si*nals at R0+

althou*h modernalthou*h modern

technolo*y does allowtechnolo*y does allow

some form of R0some form of R0

Amplifier fitted as firstAmplifier fitted as firststa*e (dotted'.sta*e (dotted'.


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0re)uency must *enerally -e lowered0re)uency must *enerally -e lowered-efore amplification can ta3e place? the-efore amplification can ta3e place? the

translation of R0 to >ower 0re)uency+translation of R0 to >ower 0re)uency+

9nown as =ntermediate 0re)uency (=0' is9nown as =ntermediate 0re)uency (=0' iscalled 4i/in*D.called 4i/in*D.

The operation ta3es place in the mi/er+The operation ta3es place in the mi/er+

and uses the $eterodyne principle.and uses the $eterodyne principle.


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# $TR5G@=@H# $TR5G@=@H=f two fre)uencies are superimposed one on another+ or=f two fre)uencies are superimposed one on another+ or

mi/ed to*ether in a suita-le circuit+ several fre)uenciesmi/ed to*ether in a suita-le circuit+ several fre)uenciesare produced? one of which is the difference fre)uency ofare produced? one of which is the difference fre)uency ofthe two7the two7

>et us ta3e one fre)uency to -e that of incomin* si*nal at>et us ta3e one fre)uency to -e that of incomin* si*nal atsay < H$% (.5. produces the secondary fre)uency which differs -y asmall amount+ say


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PRODUCTION OF VIDEOPRODUCTION OF VIDEO

PULSESPULSESThe =0 echo oscillationsThe =0 echo oscillations

are amplified to a suita-leare amplified to a suita-le

level+ and then passedlevel+ and then passed

throu*h a detector whichthrou*h a detector which

produces a dc pulse fromproduces a dc pulse from

each ac oneeach ac one

(emodulation'.(emodulation'.

The dc pulses afterThe dc pulses after

further amplification arefurther amplification are

then suita-le forthen suita-le for

application to CRT whereapplication to CRT where

they produce videothey produce videosi*nals.si*nals.


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Remainin* to -e completed -y

The class+ in accordance with $.5.

radar block

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