Comment on “Circular-to-linear polarization converter based on composite via-coupled patch frequency selective surfaces”

This comment demonstrates that in our previously study on a circular-to-linear polarization converter [Applied Physics A (2018) 124:525], the handedness of the incident circularly polarized wave was erroneously demonstrated. In the proposed composite frequency selective surface structure using four patch-via-patch modules, the diagonally truncated patch actually works as a left-handed circularly polarized antenna. Hence, the top array only responds to left-handed circularly polarized wave, instead of right-handed circularly polarized wave. This erroneous demonstration also can be founded in some other reports of polarization converter associated with circularly polarized wave due to the incorrect handedness indication when the wave propagation direction is not properly set up in commercial software.