This work deals with the replacement of the reflection layer stacks by sub-wavelength structures, which form the cavity of Fabry-Perot-Interferometer (FPI) infrared filters. Periodically arranged metal ring resonators are investigated regarding reflectivity and sensitivity with respect to polarization angle by Finite Difference Method (FDM) analysis. E-beam lithography is used for the fabrication of arrays of ring resonators made from aluminum on silicon nitride thin film substrate. The wavelength depending reflection coefficient for random polarization and for linear polarization in different directions is measured by Fourier Transform Infrared Spectrometer and compared to the results from theoretical analysis. Fixed wavelength FPI etalons are in the focus of further theoretical and experimental investigations.