CST 中waveguide port的设置问题

请问在CST中采用waveguide port源时，有如下提示：
waveguide port is too short, the waveguide must be homogenous for at least three mesh planes along propagation direction.
我能看懂上面的意思，但是我设置的波导口前的微带线很长了啊，为什么还提示我这个有问题?究竟问题出在什么地方?
谢谢。

Try to enlarge the size of the waveguide port.

By simulating many times, I found the reason that the materials defined in the simulation are not homogenous along the waveguide port propagation direction, for instance, two materials are overlapping by mistake.

能不能用汉语简单的说说整个仿真的步骤