Guilin Sun
Ansys Employee

Band structure simulation is only meant to periodic strucutures.  when the periodicity is broken, you cannot directly simuate it.

If you goal is to find its stop band, you can simulate its transmission spectrum;

Or you can simulate the periodic structure for the case without the phase shift section, and also you may simulate the phase shift section.

You may also search online to see if there is any similar publications.