Design and Implementation of Harmonic RFID Based on Conventional UHF System

There has been growing interest in the use of passive harmonic RFIDs for diverse range of applications. Conventional RFIDs are prone to self-jamming and multipath interference, and these challenges can be mitigated using the harmonic RFID design. Recently several harmonic RFID designs have been demonstrated. However, there are many designs related, packaging and intellectual property challenges associated with new tag designs. It has been well known that conventional RFIDs produce harmonic content, which is typically suppressed to reduce background noise. Previous experiments have demonstrated that the harmonics generated by conventional RFIDs can be utilized to enhance their performance. In this paper, an RFID chip is characterized for the generation of harmonic frequencies. This is carried out by designing a high frequency board that contains calibration structures along with structures to characterize the RFID chip using a one port network. An equivalent model is then developed, which in turn is used to design a dual band antenna that works at the fundamental and harmonic frequencies. In addition, the conventional RFID interrogator is modified to accommodate the measurement of harmonics generated by the RFIDs. A complete harmonic tag system is designed and implemented, and an example application of harmonic RFID is demonstrated. Here, the harmonic RFID tag is used in an industrial setting where there is large clutter (large reflections from metal structures).