Alice Buffi

A Focused Planar Microstrip Array for 2.4 GHz RFID Readers

The specific problems encountered in the design of near-field focused planar microstrip arrays for RFID (Radio Frequency IDentification) readers are described. In particular, the paper analyzes the case of a prototype operating at 2.4 GHz, which has been designed and characterized. Improvements with respect to conventional far-field focused arrays (equal phase arrays) are discussed and quantified.

Design Criteria for Near-Field-Focused Planar Arrays

A detailed performance analysis of near-field-focused planar arrays is addressed. Design curves and performance data are shown for planar square arrays as a function of the array size, the inter-element distance, and the focal distance. The performance curves are compared with results presented in earlier studies relevant to continuous-aperture antennas, as well as with numerical results obtained from a full-wave analysis of planar microstrip arrays.

A phase-based technique for localization of uhf-rfid tags moving on a conveyor belt: Performance analysis and test-case measurements

A new phase-based technique for localization and tracking of items moving along a conveyor belt and equipped with ultrahigh frequency-radio frequency identification (UHF-RFID) tags is described and validated here. The technique is based on a synthetic-array approach that takes advantage of the fact that the tagged items move along a conveyor belt whose speed and path are known a priori. In this framework, a joint use is done of synthetic-array radar principles, knowledge-based processing, and efficient exploitation of the reader-tag communication signal. The technique can be easily implemented in any conventional reader based on an in-phase and quadrature receiver and it does not require any modification of the reader antenna configurations usually adopted in UHF-RFID portals. Numerical results are used to investigate the performance analysis of such methods, and also to furnish system design guidelines. Finally, the localization capability is also demonstrated through a measurement campaign in a real conveyor belt scenario, showing that a centimeter-order accuracy in the tag position estimation can be achieved even in a rich multipath environment.

Design and performance analysis of a planar antenna for near-field UHF-RFID desktop readers

A near-field UHF (865-928MHz) RFID desktop reader antenna is designed by means of a traveling wave antenna. Since the detection of a tagged item in an arbitrary position and orientation is desirable, a meandered coplanar waveguide (CPW) line is properly designed, getting an homogeneous magnetic field amplitude. The main parameters of the RFID reader antenna (reflection coefficient, gain, effective isotropic field factor) are presented and discussed. Furthermore, the simulated and measured H-field distribution are compared, resulting in a good agreement. Finally, the overall RFID system performance is evaluated in terms of tag detection, considering short-range and long-range commercial RFID tags.

Near field focused microstrip arrays for gate access control systems

Preliminary results on the performance of near field focused planar microstrip arrays working at 1.8 GHz have been shown, with reference to an 8×8 array with linear and circular polarization. Contour plots for the field at 1.5 m from the antenna aperture have been provided. Experimental results will be shown at the conference. To reduce cost production, future prototypes will be made of four 40×40cm2 identical printed panels, connected by a suitable coaxial-cable feeding network. Finally, work is in progress to extend the research activity to systems operating at 2.4 GHz and down to 900 MHz.

A Novel Dual-Feed Slot-Coupling Feeding Technique for Circularly Polarized Patch Arrays

In this letter, a novel slot-coupling feeding technique has been adopted to realize a circularly polarized (CP) 2 × 2 microstrip array. Each array element is fed through two microstrip lines that are excited 90° out of phase (dual-feed technique) and coupled to a square patch by means of a square-ring slot realized in the feeding network ground plane. Design procedure, simulation results, and measurement data are presented for a 2 × 2 array working in the WiMax 3.3-3.8 GHz frequency band (14% percentage bandwidth). Due to both the symmetry properties of the novel slot-coupling feeding configuration and the implementation of a sequential rotation technique, excellent axial ratio (AR) performance is achieved in the WiMax band (AR < 1.35 dB at broadside) and for any direction in the antenna main beam (AR < 2.25 dB at 3.55 GHz). Actually, the 3-dB AR bandwidth is larger than the WiMax frequency band, as it goes up to about 30%.

Accuracy limits of in-room localisation using RSSI

An ML approach is able to exploit all available information, and has proven to be a powerful method to evaluate RSSI localisation methods. We plan to use it to attack problems like optimal anchor placement, exploiting multiple mobile receivers, and localisation coupled to tracking.

Analysis of near-field coupling in UHF-RFID systems

Near-field coupling analysis of UHF RFID systems is addressed. Numerical full-wave simulations are used to quantify the coupling between realistic reader and tag antennas. An impedance matrix approach has been adopted to evaluate the power transfer efficiency as a function of the distance between the reader and tag antennas, in the whole UHF RFID frequency band (860–960 MHz).

Modular antenna for reactive and radiative near-field regions of UHF-RFID desktop readers

A general and reconfigurable antenna scheme for RFID desktop readers operating in the UHF band is here proposed. To maximize the electromagnetic field in a confined volume within the antenna near-field region (namely, in both the reactive and radiative near-field regions), a travelling wave antenna is combined with a low-gain resonating antenna, which share the surface of the desktop reader antenna. The travelling wave antenna allows for covering the reactive near-field region, with almost uniform electric and magnetic fields up to a few cm from the antenna surface. The low-gain resonating antenna is used to cover the radiative near-field region, up to a few tens of cm from the antenna surface, yet radiating a relatively low field in the antenna far-field region as required by antennas for desktop readers. In such a way, a satisfactory tag readability is expected independently on the material of the item the tag is attached to and the effect of the mutual coupling among stacked tags. The suggested modular configuration can be realized by using different technologies for the travelling wave antenna (microstrip, coplanar waveguide, slotline, etc.), as well as different layouts for the resonating antenna. Above degrees of freedom allow the antenna designer to easily meet the specifications on antenna size and RFID read range. The antenna modules used to realize the reader antenna can be combined through either a shunt or series feeding connection; as an alternative, a few switches and variable power splitters could be added to implement a reconfigurable desktop reader antenna.

A modular antenna for UHF RFID near-field desktop reader

The combination of a near-field coupling antenna placed in the central area of a UHF RFID desktop reader with a low-gain resonating antenna allocated at the reader border is here proposed to obtain a confined detection volume within the antenna near-field region (including both the reactive and radiative near field regions). The antenna layout consists of a spiral Travelling Wave Antenna (TWA) which series-feeds an array of two circularly-polarized miniaturized patches. The spiral TWA geometry allows for exciting an almost homogeneous field on the antenna surface, making the tag detection on the reader antenna (near-field reactive region) almost independent on tag location and orientation. The low-gain patch array is used to extend the read range up to the radiative near-field region. Good results in terms of read range and RSSI (Received Signal Strength Indicator) distribution have been checked experimentally, also for a stacked tag configuration.