Double-Layer Cross-Embedded Holographic Antennas With Compact Size and High Efficiency

A novel and general approach is proposed for holographic antennas (HAs) to achieve high aperture efficiency with a compact aperture size. A theoretical demonstration of this behavior is found by investigating the relationship between the attenuation constant and the aperture efficiency. Meanwhile, double-layer cross-embedded tensor unit cell is proposed, to achieve more continuous surface impedance distribution. Moreover, the attenuation constant
$\alpha $
and conversion efficiency
$\varepsilon _{\mathrm {conv}}$
are improved without enlarging the aperture size and sacrificing the gain bandwidth. In this case, the double-layer topology approaches the theoretical maximum aperture efficiency with compact size. It is worth mentioning that, the proposed method is compatible with both uniform and nonuniform modulated HAs. As a validation, two double-layer HAs designed with the respective uniform and nonuniform modulation index are analyzed, fabricated, and measured. Both are with a compact aperture dimension of
$4.15^{2}~\pi \cdot \lambda _{0}^{2}$
at 26 GHz. Compared with conventional single-layer HA, the first prototype achieves an increased realized gain of 2.3 dB and an aperture efficiency of 44.3%, while the second prototype achieves an enhanced realized gain of 2.8 dB and an aperture efficiency of 49.1%, respectively. The HAs feature compact size, high efficiency, low cost, and planar integration, rendering them good prospects for the 5th generation (5G) millimeter-wave (mm-wave) applications.