Dual-Vivaldi wideband nanoantenna with high radiation efficiency over the infrared frequency band.

A dual-Vivaldi nanoantenna is proposed to demonstrate the possibility of wideband operation at IR frequencies. The antenna geometry design is guided by the material properties of metals at IR frequencies. According to our numerical results, this nanoantenna has both high radiation efficiency and good impedance-matching properties over a wide frequency band (more than 122%) in the IR frequency band. The design is based on the well-known Vivaldi antenna placed on quartz substrate but operating as a pair instead of a single element. Such a pair of Vivaldi antennas oriented in opposite directions produces the main lobe in the broadside direction (normal to the axes of the antennas) rather than the usual peak gain along the axis (end fire) of a single Vivaldi antenna. The dual-Vivaldi nanoantenna is easy to fabricate in a conventional electron-beam lithography process, and it provides a large number of degrees of freedom, facilitating design for ultra-wideband operation.