High-Efficiency Planar Reflectarray with Small-size for OAM Generation at Microwave Range

摘要： In this paper, a high-efficiency planar reflectarray with a small size 3.87λ0 × 3.87λ0 is designed, which can effectively convert arbitrary polarized waves to orbital angular momentum (OAM) waves with desired mode number and beam direction. The two concentric rings with a small size 0.38λ0 × 0.38λ0 compose the unit, which can cover the phase shifting range 360o by adjusting the ring radius. Though the developed reflectarray is much smaller than that of published ones, it can produce beams with the similar performance as large antennas. The advantages are as follows: high efficiency 22.6%, which is superior to published OAM reflectarrays, high gain 15.4 dBi, narrow divergence angle 9o, high purity, good stability, polarization insensitivity, planar structure, and easy fabrication. Using this reflective metasurface, we designed the following OAM beams: (1) OAM mode l = 1, 2, 3, 4 at (θ = 0o, φ = 0o). (2) l = 1 at (θ = 45o, φ = 180o). (3) l = 1 at (θ = 45o, φ = 270o). The above advantages are proved by the following analysis: (1) The magnitude and phase distributions in the near field. (2) The purity analysis. (3) The radiation pattern in the far field.