CST - How diffraction gratings are incorporated with metal/dielectric interface to excite surface modes in CST?

Hi, I am interested to find dispersion relation for surface modes in metal/dielectric structure. In order to excite surface plasmon polaritons, momentum of incident wave should match with the surface wave momentum. So, grating structure has to be integrated at the interface of metal/vacuum. How can this arrangement be realized in CST microwave studio?

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