Wideband Circularly Polarized Pyramidal Horn Antenna Based on Spoof Surface Plasmon Polaritons

A wideband circularly polarized (CP) pyramidal horn antenna (PHA) is proposed. A +45° or -45° rotated spoof surface plasmon polariton (SSPP) waveguide, which serves as a circular polarizer, is inserted into the PHA. The vertically polarized wave in the PHA is decomposed into two orthogonal components with equal amplitude. One component perpendicular to the circular polarizer propagates along the PHA as a fast wave, and the other one propagates along the SSPP waveguide as a slow wave. When length of the SSPP waveguide is chosen appropriately, the phase difference between these two components is +90° or -90°, which makes the PHA radiate left-handed or right-handed (LH or RH) waves. Furthermore, the phase differences approximately equal to +90° or -90° over a wide frequency range. As a result, a wideband LH or RH CP PHA is implemented. Since the SSPP waveguide is completely inserted into a standard gain PHA, its volume does not increase at all, and its appearance does not change. Measured results show that the CP PHA achieves 26% 3 dB axial ratio (AR) bandwidth (from 8.7 to 11.3 GHz), its reflection coefficients are less than -10 dB, and its gains range from 14.9 to 16.6 dBic.