An RFID tag capable of free-space and on-metal operation

The majority of commercial UHF RFID tags are based on the dipole antenna, and it is well known that tag performance degrades significantly when the tag is placed near a conducting surface. Here, we present a new antenna that operates as a dipole when in free space, but when placed on a conducting surface, it operates as a relatively efficient microstrip antenna. The antenna is shown to have near-optimal free-space performance and yield a peak gain of approximately 6 dBi of effective gain on a copper surface.