HISTORY OF RADAR
OBJECTIVE:Tostudythehistoryoftheevolutionofradarsystems to getsomeideaaboutthismarvel.
HISTORYOFRADAR:
Severalinventors, scientists,andengineerscontributedtothedevelopmentofradar. As earlyas 1886,HeinrichHertzshowedthatradiowaves couldbe reflectedfrom solidobjects.In1895AlexanderPopov,aphysicsinstructorattheImperial Russian Navy schoolinKronstadt, developedanapparatus usingacoherertubefordetecting distantlightningstrikes.Thenextyear,headdedaspark-gaptransmitter.
BEGINNINGOF RADAR:
During1897,whiletestingthisincommunicatingbetweentwoshipsintheBaltic
Sea,hetooknoteofaninterferencebeatcausedbythepassageofathirdvessel.Inhis report, Popovwrotethatthis phenomenonmightbeusedfordetectingobjects,buthe didnothingmorewiththis observation.
TheGermanChristianHülsmeyerwas thefirsttouse radiowaves todetect"the presenceofdistantmetallicobjects".In1904hedemonstratedthefeasibilityof detectingashipindensefog,butnotits distance.He receivedReichpatentNr.
165546forhis detectiondeviceinApril1904,andlaterpatent169154fora related amendmentforalsodeterminingthe distance tothe ship.He alsoreceiveda British patentonSeptember23,1904forthefirstfull Radarapplication, whichhe
calledtelemobiloscope.
RADARTODAY:
Airsurveillanceis carriedouttoday,insystemsotherthanAegis andPatriot, with mechanicallyrotatingantennas.Two-dimensional(2-D)radarsforbothmilitaryand civilsystems useparabolic reflectors atL-bandandabove,orwitharrays ofdipoleor YagielementsintheVHFandUHFbands (seeFigure1).Powertubes (magnetrons, crossed-fieldamplifiers,orklystrons)predominateinthetransmitters,as theydidin
1980.Afewsystemshavemadethetransitiontomultiplesolid-statesourcesthatare combinedinanRFnetworkfor applicationtotheduplexer andantenna.
Three-dimensional(3-D)radarsuseavarietyofantennatypes,mostbasedonplanar
arraysbutalsoincludingtheuniquearray-fedreflectorofthesolid-stateARSR-4 radar. 3-
Doperation,orscannedelectronicallyinelevat ionby phaseshiftersorfrequency- scannetworks
(andsometimesboth). Slotted-waveguidearrays havebeendesignedas ultra-low
sidelobeantennas(ULSA)reducingvulnerabilityto ECM and,as intheE-
3AWACSradar,reducingthespectralspreadingofgroundclutterreturn.Power tubes predominateas
RFpowersources forthese radars as well.
HOWRADARWORKS:
Thebasicideabehindradarisverysimple:asignalis transmitted,itbounces offan objectanditislaterreceivedbysometypeofreceiver. Thisislikethetypeofthing thathappens whensoundecho's offawall.
BasicRADARSystem:
Abasic radarsystemis spiltupintoatransmitter,switch,antenna,receiver,data recorder, processorandsomesortofoutputdisplay. Everythingstarts withthe transmitteras ittransmits ahighpowerpulsetoaswitchwhichthendirectsthepulse tobetransmittedoutanantenna. Justaftertheantennaisfinishedtransmittingthe pulse, theswitchswitches controltothe receiverwhichallows theantennatoreceive
echoed signals. Oncethesignalsare receivedtheswitchthentransfers controlbackto thetransmittertotransmitanothersignal. Theswitchmaytogglecontrolbetweenthe transmitterandthe receiverasmuchas 1000timespersecond.
Anyreceived signalsfromthe receiverarethensenttoadatarecorderfor storageonadiskortape. Laterthedatamustbeprocessedtobeinterpretedinto something.
