Are you asking how high it needs to be so that it does not interfere with the antenna and is only filtering the radiated waves? You need to be outside of the reactive field of the antenna. Very roughly this is about one or two wavelengths away.
Following on from Raymond Rumpf's answer, you would also need to be far enough away from the reactive field of FSS layer too. The evanescent plane-waves in the Floquet mode spectrum of the FSS decay exponentially as you move away from the surface. The rate of decay depends on the lattice period, lattice angles, wavelength and mode order. You would probably want to be far enough away to achieve 1/e2 amplitude decay for the lowest order evanescent Floquet mode. Hope this is what you're after:)
Ray
Dear Zinal,
In the context of the above, FSS stands for Frequency Selective Surface - a planar, periodic array of metallic elements or apertures used to filter incident electromagnetic radiation. Nothing to do with the software package, HFSS.
Okay sir understood.
Thank you very much for your time and considerations.
Regards,
http://www.ittc.ku.edu/~callen/Hi-Z_surfaces/Kern2005TAPSpp8-17.pdf,http://www.google.com/patents/US8633866. sir use this link i hope it will help you
Generally when FSS is used as a superstrate, it should be placed at a spacing of half wavelength. But to optimize the gain you have to vary the spacing a little. this is true for structures with medium bandwidth or narrow bandwidth.
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