High-Aperture-Efficiency Metamirror Using Ultra-Small and Low-Profile Monopole Elements

Sub-wavelength element is useful and attractive in high-aperture-efficiency metamirror design. In this paper, we introduce and analyze an ultra-small and low-profile monopole element, constructed based on image theorem, for metamirror applications. To the best of the authors' knowledge, the utilization of image theorem for metamirror element miniaturization is reported for the first time. Due to the effect of a metallic hole, the period of the element is decreased to 0.1125 λ₀, and the height is reduced to 0.036 λ₀. λ₀ is the wavelength at the center frequency of 13.5 GHz. In such a compact dimension, the element is readily to fabricate due to the reasonable line width, and it shows a wide reflection phase range, which is about 337°. In addition, the reflection magnitude and phase are insensitive to the incident angle over an extensive range from +60° to -60°. To verify the design strategy, a metamirror model consisting of 2724 proposed elements is built and tested. It achieves a maximum aperture efficiency of 61.05%, exhibiting a higher aperture efficiency compared with the existing designs for similar purposes.