Dear All, I know that the size of a metamaterial unit cell is usually much smaller than the free-space wavelength. This holds true to a frequency selective surface unit cell too. However, I have designed a unit cell of FSS that is comparable to half-wavelength wavelength and showed excellent performance. My question, since these unit cells are large, they are not popular. Is any aware of published work on FSS with sizes comparable to half wavelength for band reject filters applications? Thank you and best regards
I think most FSS elements are on the order of a half of a wavelength. The subwavelength versions of FSSs are called metasurfaces. Metasurfaces are used more to control phase, amplitude and polarization across the aperture of a beam. FSSs can do all of this and more, but are used mostly for frequency filtering. The main reason for wanting to minimize the element size is to reduce the element spacing so that the onset of grating lobes moves to a higher frequency. Grating lobes are normally bad since they send power in directions you may not intend. In my experience, loop type elements in a hexagonal array are usually the best in this regard.
I think most FSS elements are on the order of a half of a wavelength. The subwavelength versions of FSSs are called metasurfaces. Metasurfaces are used more to control phase, amplitude and polarization across the aperture of a beam. FSSs can do all of this and more, but are used mostly for frequency filtering. The main reason for wanting to minimize the element size is to reduce the element spacing so that the onset of grating lobes moves to a higher frequency. Grating lobes are normally bad since they send power in directions you may not intend. In my experience, loop type elements in a hexagonal array are usually the best in this regard.
Babinet principle and grating lobe theory for FSS I too suggest
Free standing FSSs (proposed by R chalil group- ESA) structures are comparable to wavelength, they work good in particular frequency range. Problem arises when you are in a need to design ultra wide band frequency response ( grating lobes). In these situations miniaturization plays important role.
FSS can be on the order of half wavelength (dipole), quarter wavelength (loop) or sub-wavelength dimension. It is true that now-a-days FSS with miniaturization is preferred more as FSS with larger dimensions occupy larger area specially for low frequency applications and when mounted with antennas.
You did not mention the substrate material. Obviously higher dielectric constants etc... radically change the material size and performance.
If the width of the surface or length of the line you are using does not hold many elements It will not work properly, because the performance depends on the periodic properties. Two rows or elements at each end may not behave properly unless they are beside a mirror such as a waveguide wall. For this reason small elements are sometimes needed. If incidence is near normal, or along a transmission line, then even close to 1 wavelength spacing can work. You need to make sure you can't launch grating lobes into the substrate where the wavelength is shortest and the direction worst. Losses should be be best with larger elements, so there is a good reason to use them if you can.
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