Circularly Polarized Antenna With Spoof Surface Plasmon Polaritons Transmission Lines

A circularly polarized (CP) antenna with spoof surface plasmon polaritons (SSPPs) transmission lines is proposed in this letter. The feeding network is based on the SSPP waveguides and parallel transmission lines. According to the dispersion characteristics of an SSPP unit and a parallel transmission line unit, a phase difference can be tuned by changing the groove depth of the SSPP unit. As a result, a feeding network is designed with SSPP waveguides to realize CP radiation. In addition, two pairs of tightly coupled dipoles are introduced as a compact radiator. The radiator and feeding network are printed on both sides of an FR4 substrate with dimensions of 85 mm × 85 mm (0.425λ0× 0.425λ0). A radiation structure is backed by a metallic ground to provide a unidirectional radiation pattern. To validate this design, the proposed antenna is simulated and measured. Measured results show that a wide impedance bandwidth of 49.4% from 1.19 to 1.97 GHz with a return loss of higher than 10 dB and a 3 dB axial-ratio bandwidth of 18.8% from 1.45 to 1.75 GHz is achieved.