Sub-Wavelength Anisotropic Unit-Cells for Low-Profile Transmitarray Antennas

This paper presents the design of a sub-wavelength (sub-WL) element with anisotropic properties and demonstrates the performance enhancement it offers for realizing low-profile transmitarrays. The transmission characteristics are analyzed and compared to those of similar half-wavelength (half-WL) elements. The results reveal that, as opposed to the half-wavelength cell, the sub-wavelength element exhibits minimal sensitivity to oblique incidence effects, a key issue for low-profile transmitarrays. To evaluate the impact of the angular robustness of the element on the transmitarray performance, four distinct prototypes with 3-bit phase resolution and 10×10 λ2 size, featuring the two unit-cell types and two different focal-to-diameter ratios (F/D = 0.85, 0.3) are designed at 30 GHz. The low-profile antenna with sub-wavelength elements attains a peak gain of 28.1 dBi with 46% aperture efficiency and a -3-dB gain bandwidth of 35%, outperforming the transmitarray based on half-wavelength elements.