▎ 摘　　要

In this letter, the input impedance and radiation efficiency analysis of graphene-based plasmonic nanoantenna (GPNA) is presented utilizing the theory of characteristic mode (CM). The total input impedance and radiation efficiency values at various feed positions are accurately and efficiently obtained as the superposition of natural CMs. Furthermore, the modal input impedances and the radiation efficiencies are also provided for in-depth understanding of the GPNA. This letter provides a new perspective to analyze the GPNA and can be easily applied to the design and optimization of other lossy plasmonic antennas with complicated geometries.