A tunable circularly polarized antenna in THz regime

Abstract

A transmissive type single layered tunable linear to circular polarization converter is realized by conglomerating both metallic and graphene patches on the same layer over a polyimide substrate. The tunability has been realized in the proposed metasurface by varying the chemical potential of the L-shaped graphene patches at the diagonal ends. Quadrature phase shift between the orthogonal components of the electric field is produced by the anisotropy caused by the double T-shaped copper patch. A tunable axial ratio (≤3 dB) bandwidth ranging from 2.57 to 3.06 THz is exhibited. To demonstrate the polarization conversion capability of the proposed tunable polarization converter (PC), a linearly polarized microstrip patch antenna (MSA) operating in the same frequency band has been designed and integrated with it. The radiated linearly polarized electromagnetic waves from the antenna get transformed into circularly polarized waves after passing through the PC. Thus, a circularly polarized antenna is realized whose 3-dB axial ratio bandwidth is tunable across 2.6–3 THz. The transmissive type PC has been placed 10 μm above the antenna to generate left-hand circularly polarized (LHCP) waves across a bandwidth of 400 GHz. The proposed simple structured linear to circular PC provides the advantage of dynamic regulation of the CP band without making any alteration in the physical structure of the antenna. Most of the reported CP antennas in THz range constitute graphene based radiating patches. They do not involve the use of metasurface for polarization conversion. For the first time, the PC integrated microstrip patch antenna has been analyzed in this work. The principle of polarization conversion has been numerically studied through full-wave simulations in CST.