Programmable terahertz vortex beam reflectarray antenna based on a graphene phoenix unit cell

In this paper, for the first time, the concept, analysis and equivalent circuit of a phoenix graphene patch (PGP) unit cell is presented. It is shown that a full 360° phase range can be realized by this unit cell, unlike common graphene patch unit cells, by only separately changing the physical or electrical parameters. Then, a reflectarray antenna based on the PGP cell is designed. The required phases are easily realized by only changing the element dimensions in the cell. The gain and radiation efficiency of the designed antenna are 26 dBi and 75%, respectively. Finally, a programmable vortex beam reflectarray is proposed, whereby the required phases are realized only by the chemical potential of the graphene sheet. The structure is discretized to five sections in the radial direction and eight sections in the azimuth direction. In comparison to other structures, the proposed design can easily generate different vortex beams in real-time by changing the biasing voltages of these sections. (paper)