Magnetoelectric-field microwave antennas: Far-field orbital angular momenta from chiral-topology near fields

TL;DR

This paper demonstrates that magnetoelectric fields near a ferrite particle with magnetic-dipolar-mode oscillations exhibit chiral topology, enabling the observation of far-field orbital angular momentum in microwave antennas, both numerically and experimentally.

Contribution

It reveals the connection between near-field chiral topology of ME fields and the generation of far-field orbital angular momentum in microwave antennas.

Findings

Far-field OAM observed in microwave radiation from a single antenna element.

Radiation pattern exhibits angular squint due to ME field topology.

Near-field ME energy distribution influences far-field radiation characteristics.

Abstract

The near fields in the proximity of a small ferrite particle with magnetic-dipolar-mode (MDM) oscillations have space and time symmetry breakings. Such MDM originated fields, called magnetoelectric (ME) fields, carry both spin and orbital angular momentums. By virtue of unique topology, ME fields are strongly different from free-space electromagnetic (EM) fields. In this paper, we show that because of chiral topology of ME fields in a nearfield region, far-field orbital angular momenta (OAM) can be observed, both numerically and experimentally. In a single element antenna, we obtain a radiation pattern with an angular squint. We reveal that in far field microwave radiation a crucial role is played by the ME energy distribution in the near-field region.