Yes, it is a strange result. May be you need to decrease the sizes of Meshing for metamaterials cells ? Or your metamaterials cells design is insensitive to such rotation of incident wave?

Dear Prof. Vadym Slyusar thank you so much for your comment, the design structure is sensitive to incident polarization according to the paper "A Fully Phase-Modulated Metasurface as An Energy-Controllable Circular Polarization Router". As long Mesh size is a concern, I didn't change mesh properties, kept the same as by default in CST. Can you please tell me what will be the appropriate size of Mesh for metamaterial cell?

As you know the sizes of metamaterials should be less than 0.1 wavelengths:

Conference Paper Metamaterials on antenna solutions

Similar to this, the sizes of Mesh cells in a general case should be less than the 0.1 sizes of slots inside metamaterials cells, which was considered in the article

Article A Fully Phase‐Modulated Metasurface as An Energy‐Controllabl...

Dear Faizan Faraz , take in your account this questionnaire as well:

https://www.researchgate.net/post/how_to_find_the_Vertical_and_horizontal_polarization_of_antenna_in_CST

Thank you so much, Dear Prof. Vadym Slyusar

-- Will the change in polarization direction have the same or different output?

Yes, but you might want to be sure about your metasurface's bi-anisotropicity. There are also nonbianisotropic cases like nb-srrs, spirals...

Aybüke Çalıkoğlu Thank you so much for responding. I am trying to check results by implementing the design structure using the article as following:

Article High-Efficiency Metalenses with Switchable Functionalities i...

But I got the same result under x and y polarization, however in the article results are different. I have attached two files in which I change polarization direction using CST. Could you please confirm is this the right way to change polarization direction or we need to do something further?

I have checked your simulation method and the proposed results in the article. Your way seems correct to me. Just to be sure, you might want to try by rotating your design under same polarization. Also, you might try waveguide excitation of CST MWS.

Good luck.