A dual-port, dual-circularly polarized OAM- generating folded transmitarray antenna for microwave imaging

Abstract A dual-port, dual-circularly polarized (CP) orbital angular momentum (OAM) generating folded transmitarray antenna (FTA) is proposed for microwave imaging applications. A dual-port, dual linearly polarized (LP) single-layer patch antenna is designed and embedded in the center of a transmitarray (TA), which serves as a feed antenna. The three-layer metal structure TA is positioned at the top to convert incoming dual-LP vortex waves into corresponding dual-CP vortex waves. A reflectarray (RA) on the bottom layer converts LP waves from the feed antenna into reflected orthogonal LP vortex waves and provides a phase compensation for generating Bessel-like vortex beams. The measured results indicate that the antenna operates within a bandwidth of 8.4–8.6 GHz (2.35%) for port 1. This frequency range can generates a left-hand CP vortex beam with an OAM mode of l = + 1. For port 2, the operating bandwidth is 8.45–8.6 GHz (1.75%), producing a right-hand CP vortex beam with an OAM mode of l = − 1. The measured peak gain of the antenna can reach up to 15.5 dBi for port 1 and 15.25 dBi for port 2. The dimensions of the antenna can be maintained at 7.7 λ 0 × 7.7 λ 0 × 1.7 λ 0 , where λ 0 represents the wavelength in free space corresponding to the center operating frequency. Using the designed OAM antenna, a microwave imaging system was developed for advanced detection applications.