Guilin Sun
Ansys Employee

Does this structure have higher order diffraction? please check the diffraction angles. Most likely it is due to PML refelction. Plese

1: use coarser mesh such as mesh accuracy 2;

2: use steep angle PML, with 32 or 64 layers

If the simulation termonates around 100%, please increase the simulation time to be 100 times longer. If it terminates before 95%, you may also need to reduce the autoshutoff min at FDTD/Advanced options

Usually shortening the simulation time is not a good choice, since the DFT result needs the time signal decaying completely.