On the Effect of Grid Orthogonalization in Stability and Accuracy of an FDTD Subgridding Method

We present a general-purpose subgridding (SG) inspired on a simplified orthogonalized integral (OI)-based method, leading to a simple and efficient algorithm with strong stability. It is based on a 2:1 transition ratio between coarse and finer zones and a natural local time-stepping (LTS) strategy to connect the domains. We provide a closed form for the stability condition and prove it heuristically, to show that roughly a 65% time-step reduction is enough to achieve stability. Results for coupling through lossy thin shells, compared with classical subcell impedance boundary methods, confirm the high accuracy of this method.