Numerical Analysis of the Reactive Energy and Q-Factor of Small Antennas

This paper aims to accurately calculate the reactive energy and determine the Q factor of small antennas using numerical calculation methods. The traditional approach of integrating the reactive energy density over the entire space around the antenna leads to infinite value. The integration domain also needs to be truncated. The numerical accuracy and efficiency are generally not satisfactory. This paper adopts an alternative formula where the reactive energy is explicitly defined over the source region. The numerically evaluated reactive energy is finite and independent of coordinate systems.