Correcting the Fabry-Perot artifacts in metamaterial retrieval procedures

We discuss the well-known limitations in the retrieval of homogenized constitutive parameters based on reflection and transmission from metamaterial slabs arising near the Fabry-Perot resonances of the samples under analysis. The associated artifacts can significantly affect the retrieval results, causing Lorentzian-like nonphysical features. We discuss the nature of these artifacts and propose a general method to correct them based on a numerical regression procedure. These concepts are applied to a homogeneous slab and a periodic metamaterial array, showing that the proposed correction can provide an improved retrieval technique for metamaterial homogenization purposes.