Terahertz Circularly- and Linearly Polarized Leaky-Wave Antennas Based on Spin–Orbit Interaction of Spoof Surface Plasmon Polaritons

In this paper, we present terahertz circularly- and linearly-polarized leaky-wave antennas based on spin-orbit interaction of spoof surface plasmon polaritons (SPPs). Besides the strong field confinement, spoof SPP waveguides inherently have longitudinal and transverse electric fields with phase quadrature, which means that the electric fields along spoof SPP waveguides have spin property. Based on the spin-orbit interaction, two terahertz circularly-polarized leaky-wave antennas are achieved with periodic cylinders: (a) by loading cylinders on top of the spoof SPP waveguide, it can excite symmetrical right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP) radiations in the transverse plane; (b) when the cylinders are loaded along the side of spoof SPP waveguide, RHCP radiation can be generated in the longitudinal plane; when the cylinders are replaced by cuboids, the RHCP radiation will become right-hand elliptical. Based on the field superposition theory, linearly-polarized (LP) radiation is achieved by elliptically-polarized waves with opposite handedness, generating by symmetrically loading periodic cuboids on both sides of the SPP waveguide. Finally, the terahertz LP leaky-wave antenna was fabricated and experimented. It achieves 14.5-17.5 dBi gain and scans from -18° to +12° in the operating frequency band of 145-220 GHz with |S₁₁| < -10 dB.