Abstract-An electrically small planar passive UHF-RFID tag based on an edge-coupled split ring resonator (EC-SRR) antenna is presented in this work. In order to explore the potentiality and limitations of the SRR antenna and to aid the tag design, an analytical study of the SRR radiation properties at its fundamental resonance is presented for the first time. Radiation resistance, efficiency, polarization, bandwidth and impedance matching with the RFID ASIC are treated in the study. Based on such analysis, the tag design process is presented, and a tag prototype of size 30 mm × 30 mm (λ 0 /11 × λ 0 /11) is designed to operate in the North-American UHF-RFID band (902−928 MHz) and manufactured. The measured read range is in good agreement with the simulation, and reaches 9.3 m at 911 MHz. The tag also features a mitigation of the blind spots, providing a minimum measured read range of 4.2 m.Index Terms -Split ring resonators (SRRs), electrically small antennas (ESAs), radio frequency identification (RFID).
A novel fully passive and electromagnetic chipless radiofrequency identification (RFID) system is proposed. The system is based on printed tags implemented with magnetoinductive-wave (MIW) delay lines. Such lines are composed of a periodic array of coupled square split ring resonators (SSRRs) and propagate slow waves. The tag is codified by introducing reflectors (which provide the identification signature) between the elements of the array. When the tags are interrogated with a pulse in time domain, they produce replicas at the positions where the reflectors are placed. Thanks to the slow group velocity of the MIW delay line, the replicas of the original pulse are not overlapped in time domain and can be demodulated, thus providing the identification code of the tag. The design considerations to implement these chipless tags are studied in the present work. Moreover, a complete set of codified MIW lines for a two-bit system is designed, manufactured and measured. The reported experimental results validate the proposed approach.
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