修改端口尺寸大小就仿真失败

现在仿真一个共面波导馈电式的天线模型，算好了波导端口尺寸大小后仿真，但是再修改波导端口尺寸大小时老是会提示这些：Number of detected conductors in port 1 has changed. The port mesh adaptation will not converge due to different mode patterns. Please check the port definition.
Adaptive port meshing failed.如果我勾选 了ensure shielding就不出现这个问题。希望各位赐教

换了一种网格类型又可以了。