Hi MEGHA_UNNI,
In the future, such questions may be more appropriately asked in the Electromagnetic Design and Simulation forum, as this one is more oriented towards theory.
On to your question:
Since you're working with a metamaterial absorber, I assume you are simulating just a single unit cell. In this case, you would want to use a Floquet port as an excitation. Floquet ports are used often to scan the angle of incidence in periodic arrays - there is a great tutorial on how to use them included with HFSS. Let us know if you have any problems with it.
Good Luck!