请问CST MWS中periodic边界条件是怎么用的

CST MWS帮助文件《Boundary Conditions - Boundaries》。
CST White Paper《Boundary and Symmetry Conditions》。
报错的具体信息都不说?

Periodic: Connects two opposite boundaries with a definable phase shift such that the calculation domain is simulated to be periodically expanded in the corresponding direction. Thus, changing one  boundary to periodic always changes the opposite boundary to periodic as well.
If you select a periodic boundary condition you may enter a phase shift for this boundary in the Phase Shift/Scan Angle property page.
Simulating antenna models with periodic boundaries enables you to examine the near field influence among the single antennas. However, note that the resulting structure represents an infinite expanded antenna pattern. To obtain the farfield of a finite pattern structure based on identical elements of the single antenna model, please use the postprocessing possibility to define an antenna array derived by the law of pattern multiplication.
好像是只能仿真无限大的阵列，同时还要设置相位差，想要仿真有限大的阵列，使用后处理功能就可以了

谢谢各位了，我现在就是想用时域来模拟像fss那样的结构，但是不知道怎么设置端口和边界条件。以为periodic和fss里的unit cell会差不多呐，但是不行。能不能给我一个用时域模拟像fss这样结构的例子啊?不胜感激。

时域的怎么模拟都是有限大的。无限的只能是unit cell