A time-domain hybrid approach that combines the Finite- Difference Time-Domain (FDTD) method with Time Domain Physical Optics (TDPO) is presented. The approach can be applied to the analysis of the backscattering of combinative objects including a Small- Size structure (SS) and a Large-Size structure (LS) with respect to the wavelength of interest. When dealing with the coupling of SS to LS, the near-to-near field extrapolation technique based on Kirchhoff's surface integral representation is used and a sequential transfer method is developed. According to the time domain calculation sequence in FDTD, the contribution of SS to LS is transferred directly to far zone observation point. The sequential transfer method has some advantages in high efficiency and small amounts of computer memory. For far zone back scattering, the influence of LS onto SS can be obtained by using the reciprocity theorem. Finally, the validation and application examples are presented, demonstrating the accuracy and effectiveness of this approach.
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