On the performance of low-profile antennas for wearable UHF-RFID tags

Main challenges while designing wearable antennas are related to the fact that the antenna platform, i.e. the human body, is a lossy non-homogeneous material. Also, input impedance, resonant frequency and radiation efficiency of the antenna are very sensitive to the distance of the antenna from the body surface, and such a distance changes randomly during natural body movements. At frequencies larger than a few GHz, it is possible to significantly reduce above coupling effects by using an antenna layout with a metallic ground plane that is large enough in terms of free-space wavelength, yet ensuring the wearer's comfort.