  Due to the mirror symmetry breaking, chiral structures show fantastic
electromagnetic (EM) properties involving negative refraction, giant optical
activity, and asymmetric transmission. Aligned electric and magnetic dipoles
excited in chiral structures contribute to extraordinary properties. However,
the chiral structures that exhibit n-fold rotational symmetry show limited
tuning capability. In this paper, we proposed a compact, light, and highly
tunable anisotropic chiral structure to overcome this limitation and realize a
linear-to-circular polarization conversion. The anisotropy is due to
simultaneous excitations of two different pairs of aligned electric and
magnetic dipoles. The 3D omega-like structure, etched on two sides of one PCB
board and connected by metallic vias, achieves 60% of linearto- circular
conversion (transmission) efficiency at the operating frequency of 9.2 GHz. The
desired 90-degree phase shift between the two orthogonal linear polarization
components is not only from the finite-thickness dielectric substrate but also
from the anisotropic chiral response slightly off the resonance. The work
enables elegant and practical polarization control of EM waves.
