Space‐time analysis of energy localization: A Poynting flow perspective with applications to pattern reconfigurable dipoles

Abstract

In this paper, we explore the dynamics of electromagnetic energy, especially in the near-field region of radiating antennas, from a fundamental perspective (ie, no limitations on antenna shape and nature of excitation signal) and identify some key future research directions. First, we provide a comprehensive critique of the frequency-domain reactive energy and circuit-theoretic Q-factor based approach, which is predominantly adopted in literature. In this way, we emphasize on the importance of adopting a general time-domain approach to characterize the near-field electromagnetic energy of arbitrary antennas. Next, we revisit the inherent ambiguities associated with the Poynting power-flux term in the context of electromagnetic energy, and point out the nonuniqueness of the reactive energy, conventionally obtained by subtracting the far-field radiation density from the total electromagnetic energy density around antennas. Furthermore, we discuss the concept of Poynting localized energy and its potential integration with FDTD techniques, and investigate its space-time behavior for a Yagi-Uda principle based pattern reconfigurable dipole system.