Effect of the metal sheet thickness on the frequency blueshift in single layer composite materials at Ka microwave frequency

The frequency shift of the transfer function of single layer composite materials has been analyzed and tested. The effects are studied by means of planar pseudo-elliptical filters in Ka waveguide. The filters, consisting of a frequency selective surface placed perpendicularly to the waveguide axis, have been realized by a high resolution photolithographic technique. Deviations of the experimental transfer functions from the simulation are analyzed with particular emphasis to the effect of metal thickness. The finite thickness of the metal constituting the frequency selective surface causes a shift of the transfer function towards high frequencies (blueshift), attributed to dipole-dipole interaction in the metal layer. Such an effect is only partially predicted by full wave analysis based on finite element method. The increase of the thickness determines a reduction of the attenuation for thickness values between 10 and 100 skin depths.