An RFID Skimming Gate Using Higher Harmonics

This paper describes a novel antenna design for communicating with ISO/IEC 14443A RFID cards at larger distances than the normal 5-10 cm. The set-up consists of two antennas, one to activate the card at the normal frequency of 13.56 MHz, and another to receive its response at the higher harmonic frequency of 40.68 MHz. The strong field required to power the card at larger distances is likely to drown out its response. By detecting the higher harmonic frequencies originating from the card's response this problem is solved, making communication at larger distances possible. The two antennas, placed 100 cm apart, form an RFID gate that can communicate with cards in the middle of the gate. This is a substantial improvement of the maximum skimming distance of 25 cm reported in literature.