Poynting Localized Energy: Method and Applications to Gain Enhancement in Coupled Antenna Systems

We present a general and comprehensive approach to evaluate spatio-temporal localized energy around radiating structures of arbitrary shapes and excitation signals. The method utilizes the finite-difference time-domain (FDTD) algorithm to calculate the Poynting localized energy for any antenna by working directly with computed fields, rather than source currents. It is established that this localized energy is fundamentally different from the classical antenna reactive energy associated with frequency-domain Q-factors of electrically small antennas. The proposed localized energy theory leads to the formulation of new performance evaluation measures, effectively going beyond traditional S-parameters and far-field patterns, which are then applied in several design examples involving strongly coupled arrays and weakly coupled antenna systems. It was found that gain enhancement caused by strong mutual coupling in the near zone (directors in Yagi-Uda systems or split-ring resonator arrays) is closely correlated with localized energy enhancement (but such correlation does not hold in weak mutual coupling scenarios). The new performance metrics are also used to generate spatial distributions for energy localization in MIMO printed dipoles. We propose that this proposed localized energy concept and the apparatus developed to investigate its relevant new data can assist in implementation of ultrahigh gain closely spaced antenna elements needed for the upcoming sub-6 GHz/mmWave 5G MIMO systems.