Soviet Work on Radar Cross Section Reduction Applicableuture Stealth Program
The a'.lhor of Ihi.f,cc pf
Scieniificand Weapon* Reieareh. Comment* and queiiej are welcome and maySWR,
udgments
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Work on Riidar Cross Section Reduction Applicableuture Stealth Program
We reel certain lhal the Soviets did nottealth program in Iheprogram that uses both body shaping and radar-absorpiive materials torue low-observable aircraft or any other platform. Because of ihe obvious high US interest in (hit area, lhc Soviets probably began an intensified research effort in thehich may have ledevelopmental program now under way.rogram could be well along before we become aware of il
For the lastears the Soviets have used wilh modestmaterials or paint on submarines, rcenlry vehicles, aircraft, and possibly on spacecraft and ground vehicles. Their results are notto the best US work, but the Soviet work has continuedmprove in both quantity and quality. Given the attention lo Stealth in lhc United State. Soviet application probably will become more widespread in the future. Mosi certainly, the Soviets will be highly motivated to assess US achievements in radar cross section reduction to improve their own position. An analysis of Soviets' opcr literature indi<aies that their understanding of the theory of isdar cross section reduction is comparable to Ihat in the United Stales
A number of Western countries also have begun programs toradar cross sections. As the technology becomes moretransfer to the Soviets could begin toignificant roletheir work
The Soviets probably wilt deploy in this decade some reirotiiicd aircraft and cruise missiles whose radar cross sections in the forward scctoi will have been reducedactoruch programs would primarily involve the application of radar absorptive materials to cutting platforms. The cross sections of bombers could be reduced in ihis manner loquare me ten those of fighter aircraft could be reducedractionquare meter; and those of cruise missiles could be reduced to less than one-hundredthquare mcicr. In some tactical engagements, such reductions wouldignificant advantage. Rel.ofilted aircraft or cruise missiles would be difficult to detect visually because ihcic would be very little change in Iheir external appearance
I
So*ie( Work on Radar Cross Section Reduction Applicableuture Stealth Program
In (reduction
The radar cross section (RCS) of any objecteasure of how much energy ii reflectsadar. Tbe amount of energy reflected is determined by ihe site, shape, and materialof the target, as well as tbe radar frequency, polarltatlon, and direction of observation. The RCS value is usuallyin units of area (square meters) or its equivalent in decibels per square metershis concept Is applicable to most platforms: aircraft, hdicopters, missiles, reentry vehicles,ships, remotely filmed vehicles, tanks, and trucks. Ships may have RCS values of0 squarend aircraft range typically fromquareBsm)quareruise missile RCS values arequare meterdBsm) loquareBsm)
RCS reductions by an order of magnitude or more often can be achieved over limited observation angles by retrofitting existing vehicles with radar-absorptive materials (seereater imprmements can be achieved with totally new designs which include body shaping as well as application ofmaterials. Such improvements require extensive research and development) efforts.
The smaller the RCS. the more difricolt it is for ibe radar io detect the target. This is particularly Iruc for low-altitude targets, because tbe radar must detect the relatively small target return in the presence of Ibe much larger return from the ground clutter. In many current air defense situations, Ihe radar return from the ground clutter greatly exceeds the return from ihe target, thus taxing to the limit the signal processing thai rejects clutter. If the RCS of an aircraftissile is reduced sufficiently, theradar will be incapable of seeing it in the presence of the ground duller
In addition, reduced RCS in aircraft can allow ihe use cf surne electronic jamming techniques that would not be feasible with rscernal target returns Self-protection jammers carried oa bombers arc limited by tbe maximum power they can cmiL Because these jammer* must compete with the strength of (he radar energy reflected from the body of the aircraft, jammer power can be reduced if Ihn aircraft RCS is reduced. Such jammers with realiiable power levels can then mall the actual radar signal re (Vet ed from the body of the aircraft and Spoof the radar by providing false positron information
In both of tbeae examples, aircraft survivability it increased.
Soiiel Radar Cross Section TecXaology Tlaeorrtical Base
Open literature has indicated lhat the Sovietshorough understanding of those aspects of electro-magnetic theory that are required to analyze and predkl RCS. Literature dealing with theory and mathematical concepts generally reflects original Soviet work, but literature dealing with applications of the concepts Is primarily from Western sources. It it also aiiparenl lhat there are more researchers in this field in the Soviet Union than in the Uniied States. Some of Ihe Soviet books examine in great detail very narrow topics almost academic in naiurt
The Sonet Open literature contains hundreds of atti-cies onheory applicahk to analysing and designing low RCS shapes although RCSis rarely mentioned explicitly. The subjectsin the articles include waveguides, cones, cylinders, edges, gratings, lossy layers, impedance
sucfaccs, anisotropic ctysials. apertures in planarand non radial ing modes in structures. Al Icasi some ol lhc works motivated by the desire to better understand and control the RCS of various platforms. The latest Soviet book on lhc Geometric Theory of Difftaction (GTD) presents all ol ihe GTD theoryottereitl fashion in one publication. GTD is the theory describing how elec-uomagnc'ic energy diffracts around edges andThis theory is one of ihe keys to understanding how much radar energy is reflected front complex objects such as aircraft.
The general Soviet understanding is also fostered through the All-Union Symposia, which are held regularly every few years. The Soviet theoretical work presented in these conferences is at least comparable in quality to the Western work in most areas
In addition to doing good quality lescarch of their own, the Soviets clearly study alt US open literature. Tltey reference the works of prominent USin iheii riubtkalions, translate US professional journals, and attend US professional conferences. For example,5 in ihe Untiedagc special issue on radar reflectivity was published at an unclassified level. Within one year, it wasy live Soviets for their own use
apability
Alihough many advances have been madeears in Ihe theoretical approach toRCS values, measurements must still be madewho work in the aiea to validate iheThe Sovietsook more lhanago ihat indicated they understand theof RCS measurements The bookmodeling, various rangescattering, nvcasutcmcni errors, andborrowingate, we have identifier
C- 3thret Outdoor RCS rncasurcinenlThere arc proba-
blynumbc ol indoorliat would be Suitable for making measurement* uf teste models live unites)
e
Stales, targets lo be nscasurccrTre usually placed on columns whose RCS have been reduced io the mint mum by shaping and treatment with radar-absor^uirc Biaicrtah Ai ibc bane the Ji ange was designed, lhc Sonets probably could acnieit smaller returns Ircanjsonmcullie cables lhan from shaped columnsery Isigc outdoor suspens-on system, being unable to precisely coeirol lhc aiimuth of ihei limit Soviet diagnoslic capability and. therefore, affect any efforts ioross sections.
ul-
econd itinge. miie ta nets
he targets have included full-size fighter aircrafi.ir missilesir-lo surface missiles, and drones, as well as scale mode
We have also
identifiedt third location
for making RCS measurements
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Measurements could be made ailhis test nngc ai allinfiaied. andthe cffecirrcrwasofpaints and coalings The facility also could be used to develop syntheticlr. in which highis achieved through signal proccssiu* of obser-valiom taken from different angle:
Maieriah
Much of lhc Sonet work in composite maieriah is probably motivated by applications other than RCS reduction. Their strength, lightness, and rigidity make them suitable for many structural aerospaceHowever, when composites are combined into layers of thin absorptive sheets, thee can rr-ii-nmin the reflection of electromagnets
The Sttvlci program for composite involve*seieniiits and engineerdata indicate
lhal So"iei ictcarch work in libcri andjiriee*probably comrunbte to thai ine if fiber work lut cinphawial aranud. thieun. and
"i liU ( i -ml .ii.iili. it
carbon fibers. The Soviets have Studied tit Uasjifferent material cooibinatioftS. wilh entphasit on conipoatlcs based on aluminum, magnesium, titanium,nd rtiekcl. Their technology base in compos-ties probably ta adequate lo support the production of an all<omposiic aircraft in. Such an air-craft, with proper shaping, has the potential oflow RCS
The Soviets alreadyood understanding of more conventional fceriie-baied radar-absorbing ma-terials as is evidencedecently published book on lhc subject The knowledge expressed in an earlier book on elastic magnetic nutefials wouldful in developing fleiible radar-absorptive materials forihe pisiform structure
Paint can also serve as the medium containing radii -absorptive material Tbe paint usually contains small fertile particles which act as small magntsi ihat lent! to realign themselves with the oscillating rleciiomag-net're field, thus absoibing ibc energy and convening it in heal Soviet ripen literature Indicates lhal ihe Soviets have ihe capabilityrepare solid iron oaides Ifcrriinl and mis ihcm into various polymeric resins, such asnd plastics, lo produce tldx'-abtorb-ing paints. The thickness of the material -illthe frequency band at which abtaepuo" will be maiimircd We do no< believe that ihe Sonets have fielded ground force vehicles pamicd wit* ladar-absotbing palm, but Iheitatuie enough lo suppon such applications in ihe. They have applied radar-absorbing paint to aircraft in ihe nasi, bui only with limited success. We aie uneensinnf ihe effectiveness of lhc Soviei point
Transfer ol Technology
Tlte United Slate is no longer ihe only Western couniry interested in reducing the RCSof .linrj't.similar work builds up in other countries, the icchnul-ngy will proliferate, making technology trsnvfci to ths: Soviet Union more likely. Some examples C ^
r
Jdata indicate Ihai lo improve their capa-biliiy in coibon/carbon composites, the Soviets hav* exploited Westein literature and conferences,W'ciicrn experts on lecture touts, and purchased hoi isostatic presses from Sweden. France, and lhc United States.
S. Ye. Satibekov noted at2 All-Union Conference on Composite Materialseview ol US literature ct^vecrning fiber/mauix interactions in metal matrix composites had ledoviet program on applying nickel coatings on graphite fibers lor graphite/aluminum composites.
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While the Stealth publicity in ihe Unitedeen concerned with only aircraft, the leehnology jnd concepts can be applied to many different platforms Indeed, lhc Soviets have allcmplcdeduce lhc RCS of several diffcrcnl kinds, although with only limited success to daic
Submarines
The Soviets have been interested in the applies lion of radar-.lbSciptnC maic'ijl*ubmarine* for mote thin JO years. Their work has included ihe following:
Krylov Central Scientific Research Institute of lln ShipbuilCling InduSlly was lOiiducling researchadar-shsoiplivc COntuigs for submarines in. Thes lo iieteimine theuiunt eombinjiions ofoxy. coiiori-gl.sss. ,md mica layers for clecuomagncnc and acuuM'C .ibsut pi inn.
Rrrnlry Vehicles
The Soviets also have long been interested in reducing the RCS of reentry vehicles.
H the Insti-isirc"drvloscow. coitabo'Hied
. I . I> . ii;hoi
crosse spgioaeiiin trcstconization in the upper ionosphere by iliiO*mg sodium oui ol ilic RV, ihei* to rcaCIhe oxygenhe ionosphere i" Crcat: .inlayerere for c. reduce ihr RCSikcly. ihe pinjee, isasdesigned'edinr; ilic KY /io reduce us .ivcuiliiie
Thet era ft currently in development haveligns of RCSit wr. believeI been wit) have features lhai willtheir RCS.nse for ihe Qand1 or eiample.resemble US mrcraft of contemporaryasShe same applies loSoviet bomber, the Blackjack, which seemsa tcahd'up version of. Anotherunder developmentis
a high-altitude, lone-endurance vehicle simitar toNone of these aircraft eshibrt any endcoceground-up configuration design ne.esssr;the minimum
Such methods of reduction probably will bein some operational Soviet aircraft af:er the mid-lvHOs. Because il typically takes ihe Soviets aboutears toew aircraft, the bomber with ihe smallest RCS eapecied tohreat lo the United States in this decade probably willlackjack, ll may incorporate the RCS reduction features jutl mentioned. The figure shows ihe upper and lower hounds of our estimates of the reduced BUcajack RCSandoHil frequencies The actual imootfced value at any aiimuih angle will probably be between ibeae bounds. The1 increase as frequency decreases. For some aiimuih angles the cross section of the bomber could be a< littlequare meter.imilar retrofit (tig, the cross sectionighter lircrsfl couldractionquare meter.
Radically new Soviet aerodynamic designs ihnl would incorporate eitensive use of radar-absorpiivccould be orwralicmal Innd have cross sections reduced by another order of magnitude Whether the Soviets choose to develop new aircraft from the ground up to minim,re the radar cross section and therefore incur aerodynamic penalties will depend on their perception of their requiicmenli.
the Soviet RCS reduction technology is not comparable to the beat US work, ihe Quality and Quantity of Soviei work over the pastears have been Increasing And sonve of the aircraft noted above now in telling probably will incorporate some tech-oiqeies lhat would reduce the RCS value by an order of magnitude in Ihe forward sector. These aircraft could include such features as conducting windshields to reflect the incident radar energy, engine inlets that are curved and/or lilted with radar-absorbingconductingomes, and earned and lined bull Scads AH of tbese techniques have been discussed in US Open literature, and the Sovietof materials and clecirom.igneiici nto supoort the implementation ol such
lackjack Radar Cross Section, >
tsxiii'ltil
C"ihIm Mlatilet
Reducing the crossons olcmite imvulc. It oneol ihe morr attractive applications because ol ibeit rnocrcntly imall lire and relatively simple shape TieSoviet cruise missiles, such as iheor eiample. could probably beo reduce the cross section froen less lhan one-ienth so lessse-hundredth ofsquire meter in the forward sector and thus improve their survivability. Work probably Is under way to reduce cross sections of cruise missiles, thus making them ready far'deployment in this decade
Ground Vehicles
An elimination ofrevealed little
evidence of ihe Servsets' attempt io reduceei However, work is probablyto measure Ihe signature of ground vehicles CThis Soviet activity could rapport -ide-
spread use of lacar-absorbirtg paint before ihe end of ihe decade We are uncertain of the paint'showever, because it would depend upon the tactical situation, the vehicles, and the technical churactrnsties of tensors observing the vehicles.
L
Appendix
Radar Cross Sectionutorial
C 'J "III focus on aerooyiiamtc Uriels. Put mosi of tne principles of RCS reduciion ire general and could be applied to other urteit as
RCS Reduction
The RCS of any radar (arict can be reduced passively in Iwo basic ways: incorporate surface shapes which minimize the reflection back in lhc direction of thetilize special materials to absorb the elect ru-maenetrc ei"g' itxideni on the tariei. C
Boay Shaping. The shaping approach can best be understood by considering Ihe radar wavelength in relation to the target dimensions The frequencyical fire-control radar is aboutHz.duces wivcicngths ofentimeters. Mostirrvcrtsions: are much larger than this, and ihe reflection can be viewed at an optical phenomenon. Most of the incident energy will be rericctod from ihe aircrcfi surfacesight beam, and the largest returns will come from surfaces that arcto the incident energy This reflection bt calledylinder willpecular return along its entire kngth when viewed fiom thephere willpecular reiurn from one spot, independent jt its orientation Some nontpecularalso occurs since the radar we.elengih ts actually not ihat of light, bul this contribution is much smaller than specular reflection in most cases Nonspecular reflectionignificantio ihe total reflected power only alter ihe specular returns have been eliminated One way to reduce the amount of energy reflected back to the radar is to shape ihe surface so thai the energy is reflected away from the radarmple, ifissile is made pointed instead of round, ihe
amount of energy reflected from it when seen ftom the from win be reduced considerably. Similarly, if the underside of an aircrafl could be made perfectlyround-based radar looking up ai the aircraft weald sec ia effectery small RCS target, because moat of the energy would be reflected away from it In both examples, lhc incident energy has been redirected by the target shape In soma direction away from Ihe radar. For some targets, there may t* aspect angles for which it it simply not feasible to ted-reel the energy For eaamolc, when viewed irom ihe side, the RCS of current-generation cruiseis very difficult to reduce.
The principal difficulty It that most shapes that !ii ra the radar return incur some aerodynamic penalties such as reduced stability, range, andThe derivation of aircraft or missilewhich minimizes the radar return whileacceptable aerodynamic performance,rea, liven more capable control syslemi will probably be needed to compensate for instabilities in low RCS designs. Baffle anangtrnents and mesh screens can be used lo hide the enginemajor contributor to ihe total reflectthe radar while still allowing air io pass through: however, ihese techniques canajor reduction in engine power. Engine inleit can be cursed, ai the expense of reduced air flow, to reduce lhc radar reflector* from tbc inlet inside walls and the engine. Inkis can also be recessed inside the fuselage to hide the opening from ihe radai. They ean be placed above the wingeduce the RCS signature when viewed from below and below the wing when viewed from above. Another technique is nonplanar inlet face starting. To reduce the RCSof engine Dorrlca. several approaches arc being considered' two-dimensional noizlca: high-aspcci ratio noules; ejector nozrks: end nozzle/airframe iniegraiinn. which will provide par-rial shielding of the opening
Before RCS reduction techniques can be integrated into practical aircraft designs, intensive analytical/ semiempirical test studies will have to be performed by the Soviet* lo roosider the interactive efTecls of different observable signatures, not only on each other bui also on aerodynamics, propulsion, configuration, and structure. Viable trades can then be esubliJhed during ihe vehicle design process. The promising aircraft configurations must then bested to validate preliminary data estimates, isolate and identify Ihe RCS coniribuwrs. and refine the designs lo funher reduce the signature levels.ccopaation between experts in aerodynamics and electromagnetics will be required, because much of the theoretical work has occurred in the academic arena. Further work will include ihe de^opmcni of new computer codes, wind tunnel and RCS measure-menu, and extensive fligirj testing.
Abtoibint Mitriials. The second principal way to reduce RCS is to utilize radar-absorbing material (RAMI. Some of the materials which could be used in RAM are graphite fibers, graphite/epoxy comrosiics. ferriies, Kevlar material, rubber, elaitomers. and plastics. The materials can be In the form of inks, sheets, honeycombs, dielectric single-core sandwiches, multilayer cores, magnetic core laminates, and hybrid sandwiches. Magnetic powders in the form ol flakes, miaospheres, and chopped wire rod can be loaded into silicone rubber and/or eposy. High dielectric constant and magnetic fillers can be added to poly-mide-based graphite/carbon resistive inks. The inks or coatings can ihen be placed on kapion film and glass/phenolic honeycomb. Some of these materials can be made readily in small quantities, bul large-quantity production may require new technologies. Improved fabrication techniques and methods of bonding these materials to aircraft structures are also needed. Radansbtorpiiue materials can be applied to mcial surfaces in those locations where ihe majority of the reflected signals arc produced or they may be used as actual radar-absorbing Structureshe use of absorbing eomposile materials for integral structural applications has Use potential to improve Mrcngth-lr> weight ratios in addition lo reducing radar stgniiiures. Much work is still required io verify the feasibility of manufacturing typical comrKysttc RAS aircraft or missile sections and tn verify the predicted performance.
liOginc inlets and exhaust noztics ofye; aircraft are large contributors to the toial reflection when viewed from the Trout or froen the rear, respectively. Sharp leading edges of ihe inlets aa as linear radiatorsTand the inlet duct may actow-attenuationThe resulting standing waves andfields can produce strong reflected fields. To date, many rr-cthods of inlet RCS reduction have resulted in only limited RCS reduction and/orperformance loss. If RAM is applied to the engine cowling lips and the inside of the inlets, ihe dectromagnetic energy will be absorbed as it is reflected inside ihe inlet, and ihe amount that is reflected back to the radar will be greatly attenuated. Tbe prir-cipal difficulty wiih this ape-roach is thai rnosi materials that are good absorbers ofenergy cannot withstand the very high tempera-tures of engine'inlets or exhausts. Thematerials presently available do not have ihe comlanaiion of mechanical and electrical properties required for integral structural design and high tem-rseraiure applications. Encapsulation of lemperaturc-sensitive magnetic panicles in insulating binders is one approach to rraorving Ihis problem. Single-ramp, iwo-dimenslonal exhaust systems have significantly more potential for RCS reduction than round nozzles. An argument against ihe use of two-dirrrensiorul exhaust systems has been the increased weight of such sysiems. bul currcni developments in carbon-carbon composite technology are expected lo provide lighter weight structural materials
New microwave-absorbing materials, materialand structural mechanical concepts musi be deveUipcd for application to future military aircraft. Most RAM is either loo heavy to apply over the entire aircraftffective onlyimited banddsr fluencies. Therefore, more ReeD is needed to reduce ihe weight and increase the bandwidth of RAM for aircraft applies lions. Radar-absorptive painthich can also be relatively heasy. could be applied to lanks without appreciably increasing the total weight. RAP would not be practica' for most aircraft applications
Oilier, more specific terAniqucs can reduce ihe RCS of aircraft. These technique* can be coniidcrcd as special cases of the aforementioned generic body shaping and materials application, approaches. Cano^ pics and windshields, which are transparent ai optical frequencies bul which are reflective at microwave frequencies, can be used to reduce the radar reflection from the inside of the esackpil. For most aircraft, cockpitsajor contribution lo ihe total reflected power because ihey contain many fal surface*.radornes can be designed in principle which will be transparent ri only one frequency, thus concealing the radar antenna from observation al all frequencies except iu own. Most avionics antennas, particularly radar dishes, increase the aircraft RCS when viewed from theimple expedient may be simply to cover the antenna bulkhead wiih absorbing material andam the radar antenna away from an observing threat radar. This mayarticularly effective approach for phased-array antennas
Sometimes RAM is incorporated in aircraft toavionics antenna performance,educe ihe RCS of the aircraft. RAM in the bottom of an airborne interceptor radome will reduce theantenna ndelobes. thus reducing the ground duller and. therefore, improving the overall rxrformaitcc of the airborne intercept radar. Radar-absorptive materials could also be used aroundairborne jammer antennas to improve their radiation paiterr
RCT, Calculations
The Iwo priricipai ways of obuining the RCSiven target are to calculate il analytically or to measure the actual vehidecale model of it.
Exaci theoretical solutions for RCS have beenforew simpleogives, and elipsotds. The usual approach to calculating ihe reflected radar poweromplex shape such as an aircraft is lo first break it down to the bask shapes for which solutions cftM. calculate thefrom each or the simple shhpes separately, and thenadd the results. Computerallow one to input entire complex bodies such as aircraft using three-view drawings inio the computer, which then carries out the necessary calculations. One of the most widely
used mathematkal tools is the GTD. Diffraction coeffidenu are used to calculate how much of the incident radar energy is diffracted around edges, and snalytk models of creeping and travelingarc ased to calculate how much energy pec-pngate* along Ihe surfaces. In the theoretical area, much more work oeeds lo be done lo improve the rrsodding of cavitks such as engine inlets, engine exhaust noMles. and cockpiu. Many of the computer corses producing the most accurate resulu also .equire inordinate run limes, and more work is weded to improve iheir effiekney as well as accuracy. Of particularis the accuracy of modeling such radome appendages a* strokes. Pilot tubes, and lithining piotection schemes
If the radar wavdertgih becomes"gtuTicert trad ion of the targetwould be the caseO-mcgaheriz IMmeier wavelength! radara cruisemethods, such as GTD. break down and other approaches must be used. One method is to model the targetarge number of conducting dcmcnis looutline the target, solve for the currents in the elements, and then calculate the net field reradioted by the currents. This approach is sometimes referred to as ihe Moment Method. One recent advance, which is showing considerableis Ihe modeling of complex surfaces using small curved patches and cakulating ihe fidd radiated by all of the patches. The analytically derived resulu may acrce with actual values to bdter. lhaiactor ofevelopment of good analytk modding tools thai can predkl the RCS values reliablyey requirement to the developmeni of new low RCS aerodynamic designs
RCS MMStireraenu
For high confidence, measurement* are still needed, particularly for new aerodynamic shapes.can be Static or dynamic; each has its advan-ibecs and disadvantages. In static measurements, the target is cither supportedok having an RCS that has been minimized or suspended from some structure using nonmctallicalibrated radar
is thento ireift strength ol ihe reflected energyunction of the aspecthcotaled The reJleetioos from the pole or ihe line* arc reduced as much as pom Mehe cootribulionshe reflection from the taigei itself But some reflection* from the target support always remain. Theiruld become particularly significant when measuring physically very large, bui low RCS urgetseavy support structure would be needed, and reflections fiom such structures can be significant. The pole mounting can provide very accurate position cemrol.
Sometimes il is noi practical to measure an aciual aircraft because of its site, weight, or unavailability. In ihatodel reduced in site can be used instead, providing the wavelength of the calibrated instrumentation radar it reduced proportionately Meaturementi using scale models have severalModeb often cannot reproduce accurately all of the RCS contributors of an actual aircraft such as cooling ports, avionics antennas, and hinged control surfaces. Also, it is not possible to measure accurately tbe effetn of any RAM application since the material properties do not scale linearlib frequency
In dynamic measure trie nit. the vehicle to be measured is actually flownalibrated instrumentation radar. This method provides the most realistic data bul only over limited aspect angles. It is also very eipentivc. and special menial instrumenton aboard ihe aircraft may be necessary to provide accurate vehicle attitude information This would be neededelate Ihe radar measurements lo the angle at which the aircraft was observed
In moat cases, radar calibration is aecornptiihed byphere of an appropriate sire since this is one of the few objecu whose RCS value is known exactly The sphere may be placedole, suspended from towers, elevatedalloon, oi dropped from un tireraft.
Fee increased security, ihe sialic tests could beoutdoors at night or indoors in anechoic chambers. Dynamic tests could be performedtrcmcl) remote local ions or ai night.
RCS tnhaaceuMwt
Sornctirncs efforts are made to actually increase the RCS. This can be accomplished by adding Luncbcrg lenses or corner reflectors to the target. Both devices have the effect of focusing the reflected energy back in ihe direction of the radar, thus increasing the re flee ted energy and, therefore, the effectiveypacal RCS enhancement application would be to make Ihe reflected signal fiom small, inopensivr target drones appear to be as Urge as from bomber aircraft in air defense egercises. Such drones also could be used to simulate aircraft in combal
Original document.
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