Oblique incidence performance of a novel two-layer absorb/transmit frequency selective surface (FSS) is investigated. The FSS has good frequency stability for both horizontally and vertically polarized waves incident normally or at oblique angles. Due to its transmission for 900/1800/1900 MHz mobile bands and good absorption for 5 GHz waves, it has the potential as a security wall or isolator for 5 GHz WLAN systems. The absorption in the stop band helps reduce additional WLAN multipath fading caused by conventional reflecting FSS designs. The first layer of the FSS consists of conventional conducting cross dipoles having a circular aperture in the centre, while the second layer uses resistive cross dipoles. Moreover, the conducting cross dipoles have been sandwiched between two dielectric sheets to achieve a stable response for different angles of incidence. The periodicity of both FSS layers is the same while the distance between the two layers is reduced to one eighth of the free-space wavelength. This reduction leads to a more compact design compared to the conventional Salisbury screen, while still achieving acceptable absorption in the stopband. Both theoretical and experimental results are presented to confirm the performance of the absorb/transmit FSS.
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