Abstract
Metamaterial superstrate is a significant method to obtain high directivity of one or a few antennas. In this paper, the characteristics of directivity enhancement using different metamaterial structures as antenna superstrates, such as electromagnetic bandgap (EBG) structures, frequency selective surface (FSS), and left-handed material (LHM), are unifiedly studied by applying the theory of Fabry-Perot (F-P) resonant cavity. Focusing on the analysis of reflection phase and magnitude of superstrates in presently proposed designs, the essential reason for high-directivity antenna with different superstrates can be revealed in terms of the F-P resonant theory. Furthermore, a new design of the optimum reflection coefficient of superstrates for the maximum antenna directivity is proposed and validated. The optimum location of the LHM superstrate which is based on a refractive lens model can be determined by the F-P resonant distance.
Highlights
Artificial electromagnetic materials, such as electromagnetic band gap (EBG) structures, frequency selective surface (FSS), and left-handed material (LHM), are broadly classified as metamaterials
The mechanism of directivity enhancement using different metamaterial structures as antenna superstrates was studied by unifiedly applying the theory of Fabry-Perot (F-P) resonant cavity
It has been shown that if the reflection magnitude p of the EBG superstrate is less than the ideal optimum reflection magnitude popt, the increase of EBG elements brings about the enhancement of the antenna directivity
Summary
Artificial electromagnetic materials, such as electromagnetic band gap (EBG) structures, frequency selective surface (FSS), and left-handed material (LHM), are broadly classified as metamaterials. The analysis and design of the high-gain antenna with EBG as the cover are based on the defect modes [19, 20] These modes involve in the superstrate and its image through the ground plane of the antenna, which are not suitable for the composite structure of a single-layer FSS superstrate [22]. In this paper, based on the theory of Fabry-Perot (F-P) resonant cavity, we further explain the unified mechanism of directivity enhancement using three different metamaterials as antennas’ superstrates. An improved design method of the optimum reflection coefficient of the superstrate for the maximum antenna directivity is proposed in terms of the F-P cavity theory. The LHM superstrate is analyzed according to the theory of the Fabry-Perot resonant cavity and near-zero refractive theory of metamaterials
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