Connective boundary's electromagnetic leakage in finite-difference time-domain

When calculating target's radar cross section (RCS) with finite-difference time-domain (FDTD), the incident wave was induced using connective boundary. In ideal situation without scattering target, there is only incident wave in total field region and the field in scattering field region is zero. But in practical calculating process, the electromagnetic wave in scattering field region is not rigidly zero because of leakage in connective boundary. In 1-dimensional situation, the leakage was measured by sum of squared electric field. In 2-dimensional situation, the leakage was measured by RCS which acquired by far field transformation of electromagnetic field in scattering field region using equivalent principle. Research results show that time step and incident angle influence the leakage very much. The leakage is small when the time step is near the least step needed for the stable requirement and the incident direction avoids impinging the connection boundary perpendicularly.