Circularly Polarized Endfire Antenna Based on Spoof Surface Plasmon Polaritons and Substrate Integrated Waveguide

In this paper, we propose a novel design of a circularly polarized (CP) endfire antenna by combining the radiation from spoof surface plasmon polariton (SSPP) structure and substrate integrated waveguide (SIW). The energy is equally divided into two paths, which propagate along the SIW and SSPP structures and generate the horizontally and vertically polarized waves, respectively. Due to the difference in the propagation constant of two transmission lines, the phase difference of 90° at two orthogonal directions is achieved, and thus a CP endfire radiation is excited by this antenna. By simulation, the 3 dB axial-ratio (AR) bandwidth of the proposed antenna is 9.3% from 26.1 GHz to 28.7 GHz, and the left-hand CP gain is above 8 dBi from 20.5 GHz to 28.2 GHz.