Complementary frequency selective surfaces

A concept in frequency selective surface (FSS) technology that stems from Babinet´s principle, whereby a hybrid of two closely coupled FSS, a layer of conducting elements and a layer of aperture elements are etched either side of a dielectric substrate, acronymed as complementary FSS (CFSS) is introduced. There are two narrow passbands separated by a distinct null. The CFSS creates electrically large elements from physically small ones to such an extent that a conventional λ/2 resonator in free space at the lower passband resonant frequency would be over three times longer than the dipole length employed in the CFSS. This passband is highly stable for normal and oblique TE and TM incidences, with less than 2% frequency shift. A full wave modal analysis is developed and two integral equations (IEs), an electric field IE and a magnetic field IE, are derived. These IEs are coupled and this renders them suitable for the solution of the CFSS problem. The interlayer dielectric region is critical to the location of the passbands as well as the in-band loss. Results are presented for dipole and ring CFSS and compared with measured data up to 40 GHz