Radiation Efficiency of Nano-Radius Dipole Antennas in the Microwave and Far-infrared Regimes

At microwave and far-infrared frequencies, the radiation efficiency of a wire antenna with a radius value smaller than a few hundred nanometers is very low, due to large wire impedances and associated high ohmic losses. However, with the continued miniaturization of electronic devices, nano-radius interconnects and antennas are desirable. In this work, the relationships among wire radius, conductivity, frequency, and ohmic loss are examined for dipole antennas. Simple formulas are derived for the distributed resistance, effective conductivity, and radius required to achieve a desired radiation efficiency, and particular emphasis is given to half-wavelength antennas. Several methods to improve antenna efficiency at sub-100-nm radius values are discussed, including the use of superconducting nanowires and multi-wall carbon nanotubes.