Enhanced Bandwidth of High Directive Emission Fabry-Perot Resonator Antenna with Tapered Near-Zero Effective Index Using Metasurface.

In this paper, a novel explanation on high directive emission of Fabry-Perot resonator antenna with subwavelength metasurface is proposed. Based on image theory and effective constitutive parameter retrieval, the whole Fabry-Perot resonant cavity structure composed of a single-layer metasurface with square ring element and a PEC ground plate can be acted as an effective metamaterial media with very low refractive index (near zero index). According to Snell's theory, this property can be used to enhance the directive emission. Based on this, with tapered size square ring unitcell, the overlapped bandwidth in which the effective refractive index is near to zero is obtained to widen the bandwidth of high directive emission. It is demonstrated that the maximum of directivity is nearly approaching to 19 dBi, and its 3-dB bandwidth can be improved to 19.5%. A final prototype has been fabricated and measured to validate the proposed design concept. The measured 3-dB gain bandwidth is approximately 20.3% with a peak gain of 17.9 dBi. These results indicate the feasibility of such kind of antenna for broadband and high directivity applications simultaneously.