Diffraction‐Limited Focusing Using a Polarization‐Insensitive Double‐Layer Huygens Metalens

Double‐layer Huygens metasurfaces offer an attractive, low‐profile alternative to complex multilayer designs, but their inherently coupled electric and magnetic responses typically introduce phase errors that severely degrade wavefront fidelity. Consequently, these ultrathin architectures often struggle to achieve the diffraction‐limited focusing required for high‐resolution millimeter‐wave systems. To overcome this fundamental efficiency‐phase trade‐off, this paper presents a double‐layer Huygens metalens engineered for diffraction‐limited operation across both orthogonal linear polarizations. By employing a symmetric and anti‐symmetric meta‐atom geometry and optimizing interlayer coupling, the proposed design suppresses parasitic phase errors, ensuring phase coverage and preserving wavefront fidelity. Experimental validation of the fabricated prototype in the K‐band confirms both its near‐field phase fidelity and far‐field system performance. Near‐field characterizations demonstrate a peak focusing efficiency of 94% at 23.3 GHz and a maximum Strehl ratio of 0.88, quantitatively confirming diffraction‐limited spatial resolution. Furthermore, far‐field measurements employing a standard horn feed validate practical applicability, achieving a total peak gain of 24.65 dBi and an aperture efficiency of 37.7%. Together, these near‐ and far‐field characterizations validate the system's practical utility, establishing the proposed metalens as a robust, low‐profile architecture for advanced millimeter‐wave beamforming and sensing.