Measurement-based infinitesimal dipole modeling for long-range OAM mode antenna analysis at E-band

Abstract

Orbital angular momentum (OAM) beams exhibit helical wavefronts characterized by topological charges, enabling multiple orthogonal modes to coexist on the same frequency channel. While this property offers potential gains in channel capacity, practical characterization of OAM beams remains challenging due to their strong divergence and the large measurement ranges required for long-distance analysis. This paper proposes a measurement-based prediction framework using infinitesimal dipole modeling (IDM) to estimate long-range OAM beam characteristics from near-field data. The electric field at the OAM aperture is represented by an equivalent set of infinitesimal dipoles obtained through an inverse dyadic Green's function formulation, enabling far-field reconstruction without additional long-range measurements. The method is experimentally validated using spiral phase plate (SPP) antennas operating in the E-band, and the predicted OAM intensity, phase, and mode-composition profiles show high agreement with measurements, yielding a correlation coefficient (CCF) above 0.9, validating the model's fidelity. The results demonstrate that IDM provides a compact and scalable framework for analyzing OAM propagation over extended distances, offering practical benefits for OAM-based wireless communication, sensing, and antenna evaluation.