The Reactive and Radiation Electromagnetic Energies of Antennas: a New Formulation

It is required to calculate the stored reactive energy of an antenna in order to evaluate its Q factor. Although it has been investigated for a long time, some issues still need further clarifying. The main difficulty involved is that the reactive energy of an antenna tends to become infinitely large when integrating the conventionally defined energy density in the whole space outside a small sphere containing the antenna. The reactive energy can be made bounded by subtracting an additional term associated with the radiation fields. However, there exists no well-founded accurate definition for this additional term that is valid for all cases. By re-checking the definition of energy densities, a new formulation is proposed in this paper to separate the reactive energy and the radiation energy explicitly. The clearly defined reactive energy is bounded without necessary to subtract the additional term, and the formulae are easy to implement.