Study On Prediction Techniques Of Radar Cross Section Of Complex Targets

ABSTRACTThis thesis puts emphasis on studying prediction techniques of radar crosssection of complex targets. Large and comp1ex targets are stUdied, Which can beairplanes or ships. In this thesis, we study both the theory and computationaltecImiques for electromagnetic scattering. The main contributions of author's workare as followst(1) The rigorous expressions of equivalent currents suggested by Michaeli isimproved by the introduCtion of a factor as transition function and some propertransformation, with new exPressions derived fOr the uniform equivalent currenswhich are finite on the shadow and reflection boundaries. For direCtions ofobservation on the Keller cone, our results reduce to the familiar expressionsproposed by Knott and Senior, and fOr points of Observation far away from theshadow and reflection boundaries, the transition function tends towards l, our resultschange into the expressions derived by Michaeli [42]. The validity of the improvedexpressions is illustrated by some numerical examples.(2) New expressions are derived fOr the fringe current components of theequivalent currents. The resulting expressions can effectively eliminate the infinitiesin incremental length diffeaction coefficient. Comparisons of numerical results withmeasurement data show that our expressions are advantageous over that of Michaeli[43] in precision.(3) A technique to solve the multiple scattering from complex targats isinvestigated. Area prOjection/physical optics method is derived fOr the computation ofthe multiple scattering. To show its versatility this method is used to calculate theRCS of both tapical struCtures such as comer refiector and complex targets such asairplane, and the results are in good agreement with the measured data or thatobtained by the FDTD method. This tecndque is easy to be integrated with othertechniques to evaluate the RCS of complex targets owing to its derivation from thePO method.(4) Various impedance boundary conditions in electromagnetic scattering areillustrated in detail. The limitation of standard impedance boundary conditions,generalized impedance boundary conditions and accurate impedance boundaryconditions are discussed, and the expressions of equivalent suffoce impedance onseveral trpical boundary conditions are presented.(5)A physical optics field analysis is derived for the scattering from dielectric flat plates, which can be used to calculate the RAM coated targets. The expressions are applied to evaluate the scattering from a wing post, and the results agree well with the measured data. The characteristics of the amplitudes and phases of electromagnetic field scattered by imperfectly conducting targets varying with surface impedance is obtained firstly by the analysis of scattering of the right-angle wedge with impedance face.(6)Some key problems on computing the RCS of large and complex targets are investigated, and the RCS of complex targets such as airplanes and ships is calculated with this scheme. The data structures for saving and access of geometric and topology information are designed. A practical method of generating polygonal wire-frame drawing and automatically obtaining geometric and topology information of targets from the DXF file of AutoCAD software is described. Furthermore, a practical algorithm for evaluating the shadowing effects is presented and the discussion of t~cet noise problem is made. The improved expressions of the fringe current components of the equivalent currents are adopted in the scattering computation, which effectively overcome the limitation of infinities in LLDC. The multiple scattering has been considered by using the area projection/physical optics method.