An Ultrathin, Low-Profile and High-Efficiency Metalens Antenna Based on Chain Huygens’ Metasurface

An ultrathin and low-profile metalens antenna based on chain Huygens’ metasurface is proposed for 28 GHz band applications. The metasurface consists of an array series of modified dipoles etched onto a piece of the dielectric substrate, and there is a half-unit dislocation along the <inline-formula> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula>-axis between these dipoles on top and bottom surfaces. Due to this geometry, the EM response between the pair of adjacent dislocated dipoles as a bridge links them into a whole structure, and thus, the metasurface is regarded as a chain structure. The chain metasurface has the characteristics of full transmission phase coverage, stable angular performance, and the subwavelength-scale EM manipulation ability (half the period of the unit along the <inline-formula> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula>-axis, <inline-formula> <tex-math notation="LaTeX">$\sim 0.215\lambda _{0}$ </tex-math></inline-formula> at 28 GHz, where <inline-formula> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the wavelength in free space). By utilizing these properties of chain Huygens’ metasurface, an ultrathin and low-profile metalens antenna operating at 28 GHz is designed with an aperture of about <inline-formula> <tex-math notation="LaTeX">$15\lambda _{0} \times 15\lambda _{0}$ </tex-math></inline-formula> and a smaller F/D ratio of 0.32 compared with the usual metalens antenna. The measurement shows that the proposed ultrathin metalens antenna achieves excellent radiated performances, including the peak gain of 30.6 dBi at 28 GHz, the antenna efficiency of 40.3%, and the 3 dB gain bandwidth of 10.7%.