Hema Singh Ebison Duraisingh Daniel J Harish Singh Rawat Reshma George Fundamentals of EM Design of Radar Absorbing Structures (RAS) 123 Fundamentals of EM Design of Radar Absorbing Structures (RAS) Hema Singh (cid:129) Ebison Duraisingh Daniel J Harish Singh Rawat (cid:129) Reshma George Fundamentals of EM Design of Radar Absorbing Structures (RAS) HemaSingh EbisonDuraisinghDanielJ CentreforElectromagnetics(CEM) CentreforElectromagnetics(CEM) CSIR-NationalAerospaceLaboratories CSIR-NationalAerospaceLaboratories Bangalore,Karnataka,India Bangalore,Karnataka,India HarishSinghRawat ReshmaGeorge CentreforElectromagnetics(CEM) CentreforElectromagnetics(CEM) CSIR-NationalAerospaceLaboratories CSIR-NationalAerospaceLaboratories Bangalore,Karnataka,India Bangalore,Karnataka,India ISBN978-981-10-5079-4 ISBN978-981-10-5080-0 (eBook) DOI10.1007/978-981-10-5080-0 LibraryofCongressControlNumber:2017945085 ©TheAuthor(s)2018 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionor informationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. 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Jha Abstract Specifically the EM absorbers are in demand for the frequency range 1–40 GHz, because of their requirement in electromagnetic interference (EMI) shielding and countermeasure to radar detection. In defence sector, stealth technology demands such EM absorbers towards radar crosssection (RCS)reduction. Total absorption ofimpinging electromagnetic (EM) waverequiresthe suppression ofall propaga- tionphenomena,viz.,reflection,transmission,andscattering.Theabsorbercanbea dielectric material or dielectric combined with metal plates placed at different intervals. The EM absorption is not difficult to achieve by increasing the volume oftheabsorbermaterialandshapingitsgeometry,providedthereisnolimitationof space and weight. However practically, the space on airborne platforms is so limited that the designer has to consider various design factors, such as weight, thickness, absorptivity, environmental resistance, mechanical strength, etc. This brief presents a detailed analytical formulation, step-by-step design procedure for EMdesignofradarabsorbingstructures(RAS).Boththeequivalentcircuitmodel and Smith chart approach are discussed with illustrations. It provides the reader a clearunderstandingofthestepsinvolvedindesigningmultilayeredRASasperthe desired specifications. This book will be helpful for beginners, academicians, and R&DengineersworkinginthefieldofRASdesignanddevelopment. Keywords Radar absorbing structure (cid:129) EM design (cid:129) Absorption (cid:129) Equivalent circuit(cid:129)Smithchart(cid:129)Reflectioncoefficient(cid:129)Admittance vii Preface Inthepresentera,lowobservabilityisoneofthecriticalrequirementsinaerospace sector, especially related to defense. The stealth technology essentially relates to shaping and usage of radar absorbing materials (RAM) or radar absorbing struc- tures (RAS). The performance of such radar cross section (RCS) reduction tech- niques is limited by the bandwidth constraints, payload requirements, and other structural issues. Moreover, with advancement of materials science, the structure geometry no longer remains key decisive factor toward stealth. There is a major contributionofRAMandRASinreducingtheradarsignatures.TheseRAM/RAS not only contribute in reducing RCS of vehicles such as aircraft or ship but also serves the purpose of reducing or even eliminating the presence of spurious radiations in the environment, caused by electronic equipment operating at high frequencies. EM absorbers are specially designed materials which can inhibit transmissionorreflectionofincidentwave.Theabsorbercanbeadielectricmaterial or dielectric combined with metal plates placed at different intervals. The EM absorption is not difficult to achieve by increasing the volume of the absorber material and shaping its geometry, provided there is no limitation of space and weight. However,practically,the space onairborneplatforms issolimitedthatthe designerhastoconsidervariousdesignfactors,suchasweight,thickness,absorptiv- ity, environmental resistance, mechanical strength, etc. This document presents a detailedanalyticalformulationanddesignprocedureforEMdesignofradarabsorb- ingstructures(RAS).BoththeequivalentcircuitmodelandSmithchartapproachare discussed.Thisworkprovidesthereaderaclearunderstandingofthestepsinvolved indesigningmultilayeredRASasperthedesiredspecifications. Bangalore,Karnataka,India HemaSingh ix Acknowledgments WewouldliketothankMr.JitendraJ.Jadhav,Director,CSIR-NationalAerospace Laboratories,Bangalore,forthepermissiontowritethisSpringerBrief. Wewouldalsoliketoacknowledgevaluablesuggestionsfromourcolleaguesat theCentreforElectromagnetics,especially,Dr.R.U.NairandMr.K.S.Venu,and their invaluable support during the course of writing this book. We would like to thank the CEM project staff, Ms. Phalguni Mathur, for assisting in editing the manuscript. IfnotfortheconcertedsupportandencouragementofSwatiMehershi,Execu- tive Editor, AppliedSciences &Engineering, of Springer, it would nothave been possible to bring out this book within such a short span of time. We very much appreciatethecontinuedsupportofMs.AparajitaSinghatSpringertowardbring- ingoutthisbrief. xi About the Book SpecificallytheEMabsorbersareindemandforthefrequencyrangeof1–20GHz, because of their requirement in electromagnetic interference (EMI) shielding and countermeasure to radar detection. Further the EMI/EMC is one of the important issues in industries related to high-speed wireless data communication systems, wirelesslocalareanetworks(LANs),mobileandsatellitecommunicationsystems, all-timemoney(ATM)machines,etc.,operatinginmicrowavefrequencyrange.In defensesector,stealthtechnologydemandssuchEMabsorberstowardradarcross section(RCS)reduction. Totalabsorptionofimpingingelectromagnetic(EM)waverequiresthesuppres- sion of all propagation phenomena, viz., reflection, transmission, and scattering. Theabsorbercanbeadielectricmaterialordielectriccombinedwithmetalplates placedatdifferentintervals.Thisdocumentpresentsadetailedanalyticalformula- tionandstep-by-stepdesignprocedureforEMdesignofradarabsorbingstructures (RAS). Both the equivalent circuit model and Smith chart approach are discussed withillustrations.Thisbookprovidesthereaderaclearunderstandingofthesteps involvedindesigningmultilayeredRASasperthedesiredspecifications.Thisbook will be helpful for beginners, academicians, and R&D engineers working in the fieldofRASdesignanddevelopment. xiii Contents 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 DesignofRadarAbsorbingStructure. . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1 Single-LayerJaumannAbsorber. . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2 Double-LayerJaumannAbsorber. . . . . . . . . . . . . . . . . . . . . . . . . 8 2.3 DesignProcedureofN-LayerAbsorber. . . . . . . . . . . . . . . . . . . . . 11 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3 EquivalentCircuitModel-BasedRASDesign. . . . . . . . . . . . . . . . . . . 19 3.1 CalculationofEffectiveAdmittance. . . . . . . . . . . . . . . . . . . . . . . 19 3.2 DerivationofCircuitElementParameters. . . . . . . . . . . . . . . . . . . 20 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4 SmithChart-BasedRASDesign. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 4.1 Single-LayerAbsorber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 4.2 Double-LayerAbsorber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 5 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Appendices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 AppendixA:ABCDVoltageMatrixAnalysis. . . . . . . . . . . . . . . . . . . . 39 AppendixB:DerivationofAdmittanceofAbsorberLayers. . . . . . . . . . 40 AppendixC:DerivationofNΓ(S)ofN-LayerAbsorber. . . . . . . . . . . . . . 42 AppendixD:SmithChart-BasedCalculations foraJaumannAbsorber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 xv