Design and Characterization of a Transmitarray for Near-Field Focusing at Sub-THz

This paper presents the design and experimental characterization of a transmitarray antenna shaping the near-field in the sub-THz band, specifically around 300 GHz. The proposed prototype consists of a pyramidal horn illuminating a planar array of 60 × 60 anisotropic unit-cells, each with a phase resolution of a 45°, corresponding to a 3-bit phase quantization. The array has been fabricated using standard PCB technology. A numerical approach, based on the Fourier Transform, incorporating the impinging electromagnetic field on the array, along with the full-wave simulated radiation patterns and scattering parameters of the unit-cells, has been employed to synthetize the phase profile on the transmitarray aperture and analyze the near-field behavior of the antenna system. A specific planar scanner has been employed to sample the near fields across two orthogonal planar surfaces, enabling the measurements of the focusing and axial behaviors of the electric field distribution. The experimental results are consistent with the proposed model and full-wave simulations, demonstrating a relatively good agreement in focus distance, spot size, and behavior along the propagation axis.