Passive RFID at Millimeter Waves

This paper introduces a novel way to implement passive RF identification (RFID) at millimeter waves. Passive operation is achieved by adding an external mixing element between the tag antenna and a standard RFID chip. The mixing element converts the RFID reader signal from millimeter waves to RFID carrier frequency-the RFID chip operates as usual. Either passive or semipassive RFID circuits at any RFID carrier frequency can be used. The reader´s TX and RX ports are similarly equipped with external mixers to convert the reader output to millimeter waves and received millimeter-wave signal to RFID carrier frequency. The paper analyses the concept theoretically with a Schottky diode as the mixing element. The design and experimental demonstration of the operation at 10 GHz are presented. Using an EPC-compliant UHF tag integrated circuit and reader, a range of 30 cm is demonstrated, but range extension to over a meter is feasible.