Representation of Electromagnetic Energy Around Antennas: Current research and future directions
Debdeep Sarkar, Said Mikki, Yahia M. M. Antar
Abstract
In this article, we reconsider the subject of spatiotemporal electromagnetic (EM) energy around the antenna near field from a fundamental perspective and discuss the use of radiation quality factors (Q factors) in this context. After a thorough literature review, we demonstrate how minimization of the Q factor and maximization of the directivity Q ratio have paved the way for the optimal design of electrically small antennas (ESAs) through the years. Then, we discuss the inherent limitations of this frequency domain Q factor approach, especially for analysis of multiresonant, ultrawideband (UWB), and nonresonant leaky-wave antennas. We further point out that the Q factor is a circuit theoretic construct valid for the steady-state, time-harmonic excitation of antennas and hence not equipped to 1) generate spatial maps of near-field nonpropagating/localized antenna energy and 2) quantify the effects of switching/pulse-like excitations on the energy dynamics.