Time-Domain Equivalent Edge Current Method And Its Application To Electromagnetic Scattering

Analysis and prediction of RCS by large complex objects is of importance inelectromagnetic scattering and related areas. Several kinds of high-frequency techniqueshave been proposed to deal with this problem. As the development of time-domainelectromagnetics, some time-domain high-frequency techniques such as time-domainPhysical Optics (TD-PO), time-domain geometric theory of diffraction (TD-GTD),time-domain uniform theory of diffraction (TD-UTD) and time-domain equivalent edgecurrent method (TD-EEC) were developed in the past ten years. In this paper, mainefforts are put on time-domain equivalent edge current method and its application toelectromagnetic scattering. Starting from basic concepts and development of the frequency domain equivalentedge current method, we analyze the process of evaluation of RCS for large complexobjects by EEC method. Based on the Fourier inversion transformation of frequencydomain equivalent edge current expression, time-domain equivalent edge currentmethod is developed. The time-domain diffraction field is expressed in terms of acontour integral along diffracting edges for arbitrary incident field with proper delaysand diffracted coefficient similar to the expression in the frequency domain, yieldingfinite results at the caustics of diffracted rays. The results for a perfectly conductingrectangular and trapezoidal flat plate, a disk and a cube computed by TD-EEC arecompared with FDTD results. The results are in good agreement while the multiplediffractions between edges are not included. The multiple diffractions evaluated byTD-EEC will be the future work. In addition, wide band RCS can be obtained throughthe Fourier transformation of time-domain scattering field. In TD-EEC method, diffraction coefficient is similar to the expression in thefrequency domain, which may be decomposed into two parts: physical optics (PO)component and fringe component. Michaeli's expression for fringe component isapplied to TD-EEC in Reference [14]. By applying the fringe component of diffractioncoefficient in [42], we obtain an improved expression for fringe component ofdiffraction coefficient implementing to TD-EEC method. An example of diffraction byperfectly conducting plate is used to illustrate our scheme. Comparing with the FDTDresults we observe that the improved expression for fringe component is more accuratethan that of Michaeli's formulation.