Francesco Alessio Dicandia

Null-Steering Antenna Design Using Phase-Shifted Characteristic Modes

A novel low-cost null-steering antenna operating at 2.45 GHz is designed by exploiting an asymmetric excitation of two characteristic modes. This compact antenna allows a null shift of the radiation pattern by changing the relative phase between the two capacitive exciters (CCEs) located above the conductive plane. As a proof of concept, a prototype of the radiator has been realized by resorting to a discrete phase shifter in order to scan the null. The measured radiation patterns prove that the proposed design strategy is reliable and applicable to other kinds of structures. The manufactured antenna is capable of steering the null within a beam of 64° centered at broadside direction (θ = 0°), with depth nulls greater than 18 dB.

An Inkjet Printed Chipless RFID Sensor for Wireless Humidity Monitoring

A novel chipless RFID humidity sensor based on a finite artificial impedance surface (AIS) is presented. The unit cell of the AIS is composed of three concentric loops thus obtaining three deep and high-Q nulls in the electromagnetic response of the tag. The wireless sensor is fabricated using the low-cost inkjet printing technology on a thin sheet of commercial coated paper. The patterned surface is placed on a metal-backed cardboard layer. The relative humidity information is encoded in the frequency shift of the resonance peaks. Varying the relative humidity level from 50% to 90%, the frequency shift has proved to be up to 270 MHz. The position of the resonance peaks has been correlated to the relative humidity level of the environment on the basis of a high number of measurements performed in a climatic chamber, specifically designed for RF measurements of the sensor. A very low error probability of the proposed sensor is demonstrated when the device is used with a 10% relative humidity level discrimination.

Analysis of the Performance Enhancement of MIMO Systems Employing Circular Polarization

The advantages of adopting circular polarization in multiple-input-multiple-output (MIMO) systems are illustrated for both line-of-sight (LOS) and multipath propagation. More in detail, an analysis of the MIMO performance attainable by employing orthogonal circularly polarized (CP) radiators with respect to orthogonal linearly polarized (LP) ones, has been addressed. At first, an accurate analysis is presented aimed at the evaluation of the channel matrix by comprehensively including also the effects of the antenna in LOS condition. In particular, the channel matrix has been calculated as a function of the antenna parameters and orientation, demonstrating that CP radiators are capable of obtaining better average values of the matrix eigenvalues with respect to LP ones. The analysis is therefore completed by evaluating the characteristics of a CP MIMO system operating in indoor environment representing this latter a more challenging condition where multipath propagation occurs. In this latter case, some meaningful numerical experiments have been performed by using a reliable ray-tracing solver, followed by a measurements campaign conducted in a real environment for validation purposes. Measurements, which are in good agreement with simulations, confirm the benefits of adopting circular polarization in MIMO systems with respect to LP.

Robust Reading Approach for Moving Chipless RFID Tags by Using ISAR Processing

A robust technique for reading moving chipless tags exploiting the inverse synthetic aperture radar data processing is presented. The procedure takes advantage from the known tag movement to improve the tag detection capability by integrating several received signals. The implicit advantage of the proposed detection scheme is that the background measurement, collected in the absence of the tag, can be easily performed before the tag passes in front of the reader antenna. The reading procedure allows for a significant increase of the interrogation distance and, more importantly, it greatly improves the detection probability in complex scenarios, where the tag is attached on arbitrary and highly scattering objects. A simplified model is used to demonstrate the capabilities of the presented procedure in detecting tags even in the presence of high clutter. Detection of tags with signal-to-noise ratio as low as −10 dB is experimentally demonstrated.

Characteristic modes analysis for pattern shaping of handheld platforms

The effects of introducing a phase-shift in the characteristic modes (CMs) of a rectangular conductive plane have been investigated. More in detail, a careful characteristic modes analysis (CMA) has been carried out in the aforementioned conditions to verify the possibility of significantly altering the shape of the overall radiated pattern. Among all the CMs, only two radiating modes (Jn) have been selected to achieve a pattern-reconfiguration ability. In particular, by a weighting linear superposition of only these two radiating modes over the conductive sheet, it is possible to realize a null-steering antenna in a principal plane. As proof of concept, a prototype of the proposed antenna has been realized and measured. The obtained results present a good agreement with the simulations and prove that the proposed design guidelines are reliable and also applicable to other kinds of structures.

Multiple characteristic modes excitation for pattern reconfigurable antennas design

The study of the Characteristic Modes (CMs) on a square conductive plane has been addressed to design a pattern reconfigurable antenna. More in detail, it is demonstrated that an efficient stimulation of suitable current modes distribution (Jn) by a proper placing of capacitive exciters over the square plate is able to provide a pattern reconfigurable capability. In particular, the positioning of the capacitive coupling exciters (CCEs) allows stimulating three current modes, whose modal excitation degree can be easily controlled. An appropriate phase shifting between the CCEs enables to control the modal excitation coefficient of the current modes, allowing the pattern reconfigurability.

Detection of moving chipless tags by using SAR processing

A technique for reading moving chipless tags by using Synthetic Aperture Radar (SAR) data processing is presented. The procedure takes advantage of the known tag movement to improve the tag detection capability by integrating several received signals. An additional unique feature of such a detection scheme is that the background measurement in absence of the tag can be performed easily before the tag passing in front of the antenna.

Chipless RFID sensor for rotation monitoring

A chipless RFID sensor exploiting the depolarizing effect of a finite period surface is proposed for rotation monitoring. The information is encoded in the cross-polar response of the scatterer, which, in turns, depends on the orientation of the chipless RFID tag with respect to the probing wave. Preliminary assessment is illustrated and critical issues are analyzed for future developments.

Pattern control for portable devices by exploiting phase-shifted characteristic modes

A pattern control for portable devices at 2.45 GHz is proposed by exploiting phase-shifted characteristic modes (CMs). Among all available orthogonal CMs, the pattern control of a rectangular conductive plane has been obtained by a weighted linear superposition of only two current modes (J4 and J8). A proper position of two capacitive coupling exciters (CCEs), hosted above the rectangular conductive plane, realize the selective excitation of the current modes, whereas the phase difference (Δθ) between the CCEs allows obtaining the pattern control. The obtained results prove that the phase-shifted CM technique is reliable and can be applicable to other kind of structures.

Advantageous Exploitation of Characteristic Modes Analysis for the Design of 3-D Null-Scanning Antennas

A novel design strategy for realizing 3-D null-scanning antennas by resorting to the characteristic modes theory is described. By exploiting the variation of the excitation degree of the current modes (