SUMMARYThe Finite Difference Time Domain (FDTD) method is one of the well-established numerical techniques to model electromagnetic problems. In order to be able to efficiently include the finer geometrical details, subgridding is used to avoid the use of a fine mesh over the whole region of interest. Our work builds on and extends the systematic framework provided by Chilton in his PhD (H-, P-and T-refinement strategies for the FDTD-method developed via Finite Element principles, Ohio State University, 2008). A crucial element of the FDTD-method is the termination of the grid in an absorbing boundary condition (ABC). With the invention of the Perfectly Matched Layer (PML) by Bérenger, this PML is now the standard ABC allowing very low reflection, even when positioned close to scatterers. In this contribution, the PML is first included into the before mentioned subgridding framework. Next, the interaction between the subgridded problem space and the (subgridded) PMLs is studied. Therefore, different (geometrical) subgridding strategies for the PML are considered. We numerically investigate the effect of these strategies by determining the reflection of a point source caused by the PML. It becomes possible to not only determine the general reflection level, but also to pinpoint the precise source of the reflections. The conclusion of this study is that important reflections are found originating from the corner points of the PML (as expected) but these reflections worsen when grid non-uniformities are present due to subgridding. Hence, the combination of subgridding and PML should be handled with great care.