  With the continued scaling of microelectronic devices along with the growing
demand of high-speed wireless telecommunications technologies, there is
increasing need for high-frequency device modeling techniques that accurately
capture the quantum mechanical nature of charge transport in nanoscale devices
along with the dynamic fields that are generated. In an effort to fill this
gap, we develop a simulation methodology that self-consistently couples AC
non-equilibrium Green functions (NEGF) with the full solution of Maxwell's
equations in the frequency domain. We apply this technique to simulate
radiation from a quantum-confined, quarter-wave, monopole antenna where the
length $L$ is equal to one quarter of the wavelength, $\lambda_0$. Classically,
such an antenna would have a narrower, more directed radiation pattern compared
to one with $L \ll \lambda_0$, but we find that a quantum quarter-wave antenna
has no directivity gain compared to the classical solution. We observe that the
quantized wave function within the antenna significantly alter the charge and
current density distribution along the length of the wire, which in turn
modifies the far-field radiation pattern from the antenna. These results show
that high-frequency radiation from quantum systems can be markedly different
from classical expectations. Our method, therefore, will enable accurate
modeling of the next generation of high-speed nanoscale electronic devices.

Mesoscale and Nanoscale Physics;Computational Physics