Abstract
Linearly polarized microwave radiation is shown to have its plane of polarization converted to the orthogonal state upon reflection from an ultrathin (λ/25) cavity array. The structure benefits from an uncomplicated design consisting of a metallic grating closely separated from a ground plane by a dielectric spacer. A single set of periodically spaced slits (monograting) exhibits polarization conversion when the normally incident electric field is aligned at 45° to the slits. Two orthogonal sets of slits (bigrating) allows this narrow-band effect to be broadened when the two orthogonal resonances are separated in frequency. We optimise the design and experimentally demonstrate near loss-less polarization conversion (95% of the incident intensity) across a 3.1 GHz frequency band. Finally, we study the dependence of the structure's performance on incident angle and slit width.
Highlights
IntroductionCircular birefringent materials possess different refractive indices for right (RCP) and left (LCP) circularly polarised radiation
Electromagnetic and Acoustic Materials Group, Department of Physics and Astronomy, University of Exeter, Exeter, EX4 4QL, United Kingdom
Linear birefringence occurs in materials where orthogonal (x and y) components of electromagnetic radiation experience different refractive indices, in devices such as half- or quarter-waveplates that convert linearly polarized radiation into 90u rotated linear or circular polarizations respectively
Summary
Circular birefringent materials possess different refractive indices for right (RCP) and left (LCP) circularly polarised radiation This provides the potential to rotate linearly polarised radiation to any desired angle provided no circular dichroism, a differential absorption for LCP and RCP waves, is present. The field of metamaterials has led to a similar result; polarization conversion upon reflection, using much thinner arrays of bianisotropic metallic elements above a ground plane These geometries include elliptical patches in the visible regime[35], dielectric cut-wire arrays[37] and ‘L’-shaped holes[36] in the infra-red, metallic cut-wires at terahertz frequencies[38], and splitrings[39,40] and ‘I’ shaped wires[41,42] in the microwave regime
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