Analysis of Near-Field EM Energy Densities for UCA-OAM Wave Based on Infinitesimal Dipoles

This paper demonstrates the significance of employing the infinitesimal dipole modeling (IDM) in analyzing uniform circular array-orbital angular momentum (UCA-OAM) near-fields in terms of electromagnetic (EM) energy densities. The electric and magnetic field, and the EM energy densities of UCA-OAM waves are theoretically analyzed and numerically estimated where the spatial distribution of EM Lagrangian density and complex Helicity is visualized. It is validated that the IDM is more accurate than the conventional far-field assumption in evaluating the near-fields of UCA-OAM waves as the EM Lagrangian density and the complex Helicity are clearly depicted based on the IDM, while they are unobservable with the far-field assumption. The visualization of EM Lagrangian density and complex Helicity can be beneficial in designing UCA-OAM communication system as it suggests the mutual coupling between antennas by describing the regions of reactive EM energy densities and non-orthogonal EM fields in the near-field region.