Broadband Metasurface Antenna Using Hexagonal Loop-Shaped Unit Cells

A broadband metasurface antenna with a novel hexagonal loop-shaped unit cell structure is presented. A hexagonal loop element array is proposed as the main metasurface radiator, which is aperture-fed through a microstrip line and a coupling slot. The bandwidth can be broadened from two perspectives. On the one hand, the proposed hexagonal loop element is capable of generating broadband radiating bandwidth. On the other hand, due to the shape of the hexagonal loop structure, gaps between unit cells lead to a larger equivalent capacitance. This larger capacitance significantly pulls the fundamental resonant frequency downward, compared with conventional square structures, consequently leading to the broad bandwidth. In the design, the broadband performance is achieved by utilizing five TM modes at five resonant frequencies in the operational band from 4.65 GHz to 8.3 GHz. Apart from the fundamental TM01 mode, only TM12 modes were excited in different parts of the metasurface layer at different frequencies. This has ensured that the proposed antenna can maintain a stable radiation pattern in the desired band. The operation of the proposed antenna is analyzed in detail. The proposed hexagonal metasurface antenna with an overall size of $1.1\,\lambda _{0} \times 1.1\,\lambda _{0} \times 0.06\,\lambda _{0}$ can achieve 56.3% fractional bandwidth and a gain ranging from 7 to 11 dBi, which can be employed in satellite, radar, and wireless communication systems.