Rfid Antenna Design For The Internet Of Things Applications

Radio frequency identification (RFID) is a non-contact technology which uses radio signal to achieve data exchange and automatic identification on static and moving objects.In recent years, UHF near-field RFID has been widely used for item-level tagging applications in retail industry. Developing chipless tags with no ICs to reduce the RFID expense is a trend of RFID future development. Therefore, the UHF near-field reader antenna and the chipless tag are studied in this paper.Read range and far-field gain are always two key factors for UHF near-field reader antenna design. The UHF near-field RFID system is based on inductance coupling. Reader antenna is usually made of a circular loop, while the diameter is much larger than the wavelength, a change in sign of current flow will produce little magnetic field on the axis. In this paper, the effective radiation current which provides analysis for optimizing the reading distance and far-field gain is first proposed. Based on this, a new segmented-resonant loop antenna is designed, which is much easier to adjust sizes to resonance to achieve uniform and unidirectional current along the loop. The optimized antenna has a dimension of×752×35mm3. The measured bandwidth is19MHz (853MHz-872MHz) under the condition of VSWR<2, which covers the European UHF band completely. In addition, the simulated far-field gain is OdBi and the measured reading distance is130mm in the operating band.In this paper, a spectral signature-based chipless tag is designed, which is consisted of a horizontal polarized monopole antenna, a spiral multi-resonator and a vertical polarized monopole antenna. The frequency swept signal sending by the reader is introduced attenuations at particular frequencies by the15spiral resonators, so the reflected signal includes15bit spectrum signature. In the operating band (3.3GHz～4.7GHz), the measured VSWR of monopole antennas are less than2and the measured S12of the filter matches well with the simulated result. In addition, the chipless RFID system is measured using a vector network analyzer and the measured S12basically satisfies the demand.