An Ultralow-Profile Folded Transmitarray Antenna With Both-Sides Beam Regulate for K-Band Circularly Polarized OAM Waves

An ultralow-profile, high-gain folded transmitarray antenna (FTA) for generating the orbital angular momentum (OAM) is proposed in this letter. The folded antenna consists of a receiver/transmitter (R/T) structure metasurface and a metal plate reflector. By controlling the rotation of the R–T structural unit cells, independent manipulation of transmission and reflection of incident waves is achieved. Simultaneously, multiple reflections between the two plates reduce the antenna's height, making our design's height-to-focal ratio (H/F) significantly lower than the conventional folded structure of 1/3. The proposed antenna has dimensions of 7.4<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ₀</i> × 7.4<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ₀</i> × 1.86<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ₀</i> and can generate an OAM beam with mode <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> = +1 at 20.6 GHz to 22.4 GHz with a peak gain of 17.35 dBic. Throughout the entire frequency band, the axial ratio remains below 1.5 dB, enabling the generation of CP vortex beams. This indicates that our design structure holds great potential in miniaturized OAM wireless communication.