Design Of Polarization Converters Based On Frequency Selective Surface

Frequency selective surfaces(FSSs)have garnered vast investigations for a long time as its applications in electromagnetic wave control.Frequency selective surface is usually a periodic structure composed of artificially designed element according to its specific functions.It can be used in many fields,such as radome,sub-reflector and EM-shielding.In recent years,polarization converters realized by FSSs have gained extensive research interests.In this thesis,we intent to investigate the polarization converters based on FSSs in transmission mode.The frequency response of the converter is determined by the FSS unit cell that we designed by using antenna-coupler-antenna modules.The polarization conversion is determined by polarization of the receiving and transmitting antennas.Based such an approach,six polarization converters with different polarization conversion have been proposed,and the experimental and simulated results agree well with each other.Main achievements include:(1)Taking the top receiving and bottom radiative antennas as an orthogonal planar dipole pair in-lined by a pair of through-via holes passing through the perforated metal shielding layer to form the FSS unit cell,a dual-frequency band 90 degree linear polarization converter is presented.(2)Taking the top receiving and bottom radiative antennas as two orthogonal planar dipole pairs in-lined by two pair of through-via holes passing through the perforated metal shielding layer to form the FSS unit cell,a dual-frequency band vertical-to-horizontal(or vice versa)linear polarization converter is presented.(3)Making a planar orthogonal inverted-L antenna pair to be the receiving antenna,and another pair with mechanically phase-changed by 180 degrees to be the transmitting antenna,a new FSS unit cell is formed to realize an arbitrary angle linear polarization converter.(4)A planar loop-antenna pair in-linked by a pair of through-via holes passing through the perforated metal shielding layer is introduced to build the FSS element,a right-to left-handed(or vice versa)circularly polarization converter is presented.(5)By using planar single spiral and crack circular patches as the circularly polarized antenna elements,left-to right-handed(or*or vice versa),left-to left-handed and right-to right-handed polarization conversion modules are presented.Composite FSSs can be formed by selecting the first and second or third modules,which can realize right-and left-handed circular-to-linear polarization converters,respectively.