Amrita Pati
Ansys Employee

Hi Joohyung,

Thanks for sharing additional information! Looks like you need to use FDTD to simulate this, other approximate methods won't work well for this geometry. But I will recommend you to use Symmetric/Anti-Symmetric BCs, they can leverage the symmetry of the structure and fields to reduce the computational domain and thus the resource requirements. Please use this link to learn more about them: Symmetric and anti-symmetric BCs in FDTD and MODE. As for the mesh accuracy, you can try a lower mesh accuracy for the intial tests, but eventually, I will recommend you to perform convergence testing with respect to the mesh resolution to confirm the accuracy of the simulation. 

Regards,
Amrita