Broadband Dual-Polarization Thin Aperture Based on Dense Arrangement of Subwavelength Unit Cells for Low-Profile Transmitarray Antenna

method for designing broadband dual-polarization thin aperture with a small focal length to diameter ratio ( F / D ) is proposed for low-profile transmitarray antenna (TA). The aperture is composed of two types of narrowband subwavelength unit cells, namely the wire-loop Huygens' unit cell and the stacked I-shaped cross unit cell. The two types of unit cells collaborate to achieve complete 360° phase coverage and uphold a high transmittance (>-1.3dB). Both unit cells possess the capability to manipulate dual polarization electromagnetic (EM) waves, exhibit strong angular stability, and have a period of 0.165λ 0 (where λ 0 is the free space wavelength at 9 GHz). Furthermore, the subwavelength period of the unit cells enhances the sampling frequency of the aperture, thereby effectively mitigating aperture distortion caused by unit cell failure resulting from frequency variations. Hence, despite the narrowband nature of the unit cells, the aperture enables broadband performance. The proposed aperture design method offers a more efficient solution for broadband small F / D compared to the conventional TA design method, with reduced design complexity, thinner aperture thickness, and simplified unit cell structure. Finally, the proposed methodology is utilized to design the aperture of a TA prototype with an F / D of 0.32, which is equipped with a broadband magneto-electric (ME) dipole feed. The measured results demonstrate that the 2.5-dB gain bandwidth of the TA prototype is 17.02%.