Hi AndyJP,nnI ran the simulation with finer meshes. It seems finer meshes over more passes can help with convergence. In addition, another issue comes into my view. Since the solution frequency is complex, we need to understand the physical meaning of both real and imaginary parts. From one paper I read, the imaginary part, when it is greater than zero, represents the attenuation of field over time. However, I have seen the eigenmode solver returns solution frequencies with a negative imaginary part. In that case, if we use the same interpretation above, it would represent amplification of fields over time, which is not physically possible. May I know your opinion on the imaginary part of the complex solution frequency being negative?n