High-Efficiency Planar Reflectarray With Small-Size for OAM Generation at Microwave Range

In this letter, a high-efficiency planar reflectarray with a small size of 3.87λ₀ × 3.87λ₀ is designed, which can effectively convert arbitrary polarized waves to orbital angular momentum (OAM) waves with a desired mode number and a beam direction. The two concentric rings with a small size of 0.38<italic>λ</italic>₀ × 0.38<italic>λ</italic>₀ compose the unit, which can cover the phase-shifting range 360° 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 9°, high purity, good stability, polarization insensitivity, planar structure, and easy fabrication. Using this reflective metasurface, we designed the following OAM beams: first, OAM mode <italic>l</italic> = 1, 2, 3, 4 at (<italic>θ</italic> = 0°, <italic>ϕ</italic> = 0°); second, <italic>l</italic> = 1 at (<italic>θ</italic> = 45°, <italic>ϕ</italic> = 180°); and third, <italic>l</italic> = 1 at (<italic>θ</italic> = 45°, <italic>ϕ</italic> = 270°). The above advantages are proved by the following analysis: the magnitude and phase distributions in the near field, the purity analysis, and the radiation pattern in the far field.