Broadband Bilayer Antireflective Coating with Metasurfaces and Chebyshev Transformer

Antireflection coatings with a broad relative bandwidth (RBW) and reduced electrical length are desirable for a variety of applications in the microwave frequencies. Here, we propose the design principle of bilayer metasurfaces with 100% RBW and subwavelength thickness based on the traditional Chebyshev transformer, with excellent agreement with our experimental validation for both transverse electric and magnetic polarizations. We utilize the multiple-beam interference theory to reveal the underlying mechanism of the preferred choices for nonresonant or weakly resonant metasurface unit cells. Being able to manipulate the transmissions and reflections within the bilayer structure, we further demonstrate the universality and sensitivity of the designs capable of providing near-unity microwave transmission from air into the full range of natural media, with prescribed RBW and reduced electrical length.