Near-field RFID Applications Research Articles

Broadband cross dipole antenna for UHF near-field RFID applications

Broadband cross dipole antenna for UHF near-field RFID applications

Electrically Large Segmented Dipole Array Antenna With Reflectors for UHF Near-Field RFID Applications

A novel electrically large segmented dipole array antenna with reflectors for ultrahigh-frequency near-field (NF) radio frequency identification applications is proposed in this communication. It consists of eight electrically large segmented dipoles and two reflecting plates of convex parabolic shape. Each dipole has 12 identical parts connected by appropriate capacitive loads, which almost achieves an in-phase surface current distribution. The two plates act as reflectors to limit the strength of the NF magnetic fields outside of the reading area and to improve the impedance matching. The proposed antenna generates a strong and uniform magnetic field distribution in a finite area, which could effectively reduce the misreading rates outside of the interrogation zone. A prototype was fabricated and tested for verification. The measured results showed that a strong and uniform magnetic field distribution was generated within an interrogation zone of $480\,\,\text {mm} \times 300$ mm. A broadband of approximately 117 MHz ( $\vert \text{S}_{11}\vert dB), from 843 to 960 MHz, was achieved, covering the ETSI and FCC standards.

A Reader Antenna for UHF Near-Field RFID Applications Based on the Segment-Line Oppositely Directed Currents

A reader antenna based on the segment-line oppositely directed currents is proposed in this letter for the ultrahigh frequency near-field (NF) radio frequency identification applications. The proposed antenna consists of two identical electrically large dipole elements without additional impedance matching network. To keep the surface currents along the dipole elements in-phase, the segmental and loaded method is adopted. Through the dispersion analysis, the maximum length of the dipole elements is one and a half guide wavelength with 12 segments and 0.7 pF lumped capacitors at 920 MHz. Subsequently, adjusting an appropriate distance between the dipole elements can form the oppositely directed currents, resulting in a strong, uniform, and large NF magnetic field distribution. The measured results show that the bandwidth is 53 MHz from 884.5 to 937.5 MHz covering the FCC standards. The interrogation zone is approximately equal to 480 mm × 250 mm under the observing height of 50 mm above the antenna surface. Thus, the proposed antenna is suitable to be used for the smart showcases and shelves.

Design of near‐field ultra‐high frequency radio‐frequency identification antenna with fragmented wires for electrically‐large coverage

Design of ultra-high frequency radio-frequency identification (UHF RFID) reader antenna covering electrically-large near-field area is still challenging for near-field UHF RFID applications. In such design, magnetic field distribution on a large coverage area is required to be as uniform as possible. Fragment-type wire antennas are quite suitable for such demand because distribution of fragmented wires in a designated electrically-large area can be optimised to counterpoise the magnetic fields generated by non-uniform current distribution. By optimisation searching with multiobjective evolutionary algorithm based on decomposition combined with enhanced genetic operators, fragment-type RFID reader antenna is designed to provide uniform magnetic field distribution within dynamic range of 4 dB in an electrically-large near-field coverage of 320 × 320 mm at 915 MHz. The designed antenna is fabricated and tested. Both simulation and measurement results show good impedance matching, satisfactory near-field coverage, and desirable omni-directional pattern.

Subsystem of Phased Array Antennas With Adaptive Beam Steering in the Near-Field RFID Applications

An antenna subsystem is presented for RFID reader applications at 2.45 GHz in the near-zone tag detection. The subsystem is programmable to adaptively steer the radiation beam from one spot to another inside the target zone, and allows the RFID to achieve a better signal reception by changing the beam patterns along the horizontal cut. The created beams have narrow spots, and may potentially reduce the interference by the electromagnetic scattering from the nearby metal structures. An antenna prototype is examined to validate the feasibility.

Meandered TWAs array for near‐field UHF RFID applications

An array of 2 × 2 travelling wave antennas (TWAs) is proposed for near-field RFID applications in the UHF band (865-928 MHz). Each array element is characterised by a meandered line based on coplanar waveguide technology. All the TWAs end on a matched load, which allows for non-stationary current and field distributions as well as a low far-field gain. Thus, strong and uniform fields within a confined volume above the antenna surface have been obtained, with a field maximisation in the antenna central area, where tagged items are supposed to lie on. The meander geometry allows exciting all-field components, making the tag detection almost independent of tag location and orientation when it lies on the antenna surface. Since TWAs are not resonating structures, the proposed antenna results are scalable, allowing for an easy integration in commercial readers with arbitrary sizes. In particular, a 275 × 135 × 10 mm 3 antenna has been designed to fit a particular commercial desktop reader size. Measured tests on the antenna read range were carried out, showing a field distribution maximised in the broadside direction within 10 cm from the antenna surface.

A Reconfigurable Passive UHF Reader Loop Antenna for Near-Field and Far-Field RFID Applications

This letter presents a passive UHF printed loop antenna with left-handed loading. The RFID reader antenna can work at near- and far-field operation within the European UHF (865-868 MHz) band. The operation frequency and radiation properties can be modified by employing varactor diodes. Also, the antenna can work in the near-field region having a flat magnetic distribution in the interrogation zone. A comparative study with other passive RFID reader conventional antennas shows that the left-handed loop achieves stronger near H-field with good impedance matching. Design details, simulated results, and a fabricated prototype are presented. The concept significantly extends the design degrees of freedom for RFID antennas.

Microstrip-based segmented coupling reader antenna for near-field UHF RFID applications

A microstrip-based segmented coupling reader antenna is proposed for near-field ultra high frequency radio frequency identification applications. The measured reading distance is 13.5 cm in the air and the measured bandwidth is around 55 MHz (895–950 MHz) under the condition of voltage standing wave ratio less than 2.0, which covers the Federal Communications Commission standard (902–928 MHz) completely. In addition, the simulated far-field gain is around 4.7 dBi. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26144