HFSS metamaterial design solution type and port setting problem

I am trying to make some structure shown in the attach picture. This structure should have uniform near field magnetic field on one side of it.
As it is differential mode, so I was trying to use driven terminal. But when I set the wave port, it says that no conductor found on the port. I am sure I set the material right and there do is conductor connected to the port. So what is the problem here? Need help. THANK YOU.

Is this structure some kind of left hand material?

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If the conductor are made just striplines, this problem wont come out.
But this loop-line structure will have this problem
so what is the problem indeed?

I also met the situation that one of the two port was set successfully but the other failed.