Dipole Antenna with Multiple Feeds Adapting to the Environment

This paper studies single-fed and multiply-fed dipole antennas for RFID tags and their application. One major problem affecting the performance of an RFID tag is the variation of feed-point impedance when the antenna is attached onto media with different dielectric permittivity. It is proposed to switch between different feed-points of the antenna to reduce feed impedance mismatch. This study identifies the worst-case level of reflection coefficient magnitude of dipole antennas with a single feed and with two feeds, while varying the positions of the feed points, for a scenario where the antennas are attached to a dielectric half-space of relative permittivity ranging from 1 to 50.