Energy-Based Considerations for Ungrounded Wearable UHF Antenna Design

The robustness of wearable UHF-band ungrounded antennas with respect to body-coupling effects is addressed. Two different configurations of single-layer antennas, with different energy density distributions, are presented, and a design criterion to improve their performance with respect to the antenna-body separation is derived. Through an analysis of the antenna electric and magnetic energy density distributions, it is shown that the degradation of the antenna performance due to the proximity of the human body can be reduced if the electric energy density is confined in specific regions far from the antenna border. The proposed design criterion has been validated by numerical simulations and experimental measurements.