Quadrature-Spoof Surface Plasmon Polariton Unit Cell With Circuit Characterization for Circular-Polarization Generation

Abstract

A quadrature-spoof surface plasmon polariton (SSPP) unit cell (QS-UC) is proposed and theoretically characterized for circularly polarized (CP) wave generation. The proposed QS-UC is composed of a fishbone SSPP waveguide (FSW) and a spine quadrature mode converter (SQMC), which converts the SSPP mode into a quadrature radiating mode. An equivalent circuit is established to derive the cascaded ABCD matrix and the conditions for quadrature CP generation. Scattering parameters and dispersion characteristics are extracted from the established circuit model. The generated CP far-field wave is calculated through the quadrature-mode current distribution on the SQMC. The theoretically calculated results are also compared to the EM-simulated results, with good agreement. Based on the proposed QS-UC, a quadrature SSPP linear array (QS-LA) is developed, fabricated, and measured for the verification of CP generation. Detailed measured results show that the developed QS-LA has a wide impedance bandwidth of 5.28-11 GHz (70.3%). More importantly, the developed QS-LA shows a wide CP bandwidth covering 5.8-10 GHz (53.2%), with CP beams covering (-65°, 16°) for right-hand CP(RHCP) generation at port 1 and symmetrical range of (-16°, 65°) in left-hand CP(LHCP) generation at port two. These excellent performances verify the effectiveness of the proposed QS-UC in CP generation.