Roberto Caso

A Wideband Slot-Coupled Stacked-Patch Array for Wireless Communications

In this letter, a novel slot-coupling feeding technique is used to realize a dual-polarized 2 × 1 microstrip stacked patch array for mobile wireless communication systems. The array is intended as a basic module for base-station linear arrays, whose final size depending on beamwidth and gain requirements. Each array element is fed through two microstrip lines arranged on the basis of a sequential rotation technique. Each stacked square patch is excited through a square ring slot realized in the feeding network ground plane. Design procedure, simulation results and measurement data are presented for a 2 × 1 array working in the GSM 1800-1900 band (1710-1910 MHz), UMTS band (1920-2170 MHz), ISM band (2400-2484 MHz), and UMTS 3G expansion band (2500-2690 MHz) or, alternatively, WiMAX band (2300-2700 MHz), with a resulting 45% percentage bandwidth (reflection coefficient <; -10 dB). Due to both the symmetry properties of the novel slot-coupling feeding configuration and the implementation of a sequential rotation technique, good results have been obtained in terms of port isolation and cross-polar radiation patterns.

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.

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%.

Dual-Band UHF-RFID/WLAN Circularly Polarized Antenna for Portable RFID Readers

A compact, low-profile, two-port dual-band circularly polarized (CP) antenna for portable RFID readers is presented. The radiating element for the UHF-RFID band (902-928 MHz) has been realized through a circular array of four inverted-F meandered monopoles, where the array elements are excited with a 90 ° phase offset (sequential rotation feeding technique) through a microstrip feeding network. In order to also provide the portable reader with a wireless web access, a miniaturized CP patch has been added for the WLAN IEEE 802.11b,g radio link, by exploiting the available space between the four array elements, without increasing the overall antenna volume. The meandered monopoles and the patch are both etched on the same layer of an FR4 substrate, so getting a significant antenna compactness (60 mm×60 mm×7 mm). The patch loading effect on the monopoles can be compensated by adjusting the meandered monopole length. Reflection coefficient, port isolation, axial ratio and radiation patterns are evaluated by numerical simulations and compared with measurements on an antenna prototype.

A Compact Dual-Band PIFA for DVB-T and WLAN Applications

A compact dual-band Planar Inverted-F Antenna (PIFA) working in both the DVB-T (Digital Video Broadcasting-Terrestrial) and the WLAN (Wireless Local Area Network) IEEE 802.11b,g frequency bands is presented. It is designed to be integrated in a monitor-equipped device, and exhibits reduced electrical size with respect to similar PIFA configurations. A reflection coefficient less than -6 dB and -10 dB was obtained in the 470-862 MHz (59% percentage bandwidth) DVB-T and the 2400-2484 MHz (2.7% percentage bandwidth) WLAN bands, respectively. An antenna gain of almost 3 dBi and 4.5 dBi, with more than 95% radiation efficiency, was obtained in the two frequency bands of interest. The PIFA fills an overall volume of 217 × 12 × 8 mm3 and can be realized by a properly cut and fold single metal sheet. Measurements on prototypes have shown that the proposed layout is robust in terms of the impedance matching detuning that can be caused by the presence of metal parts nearby the antenna.

Numerical Analysis of a Wideband Thick Archimedean Spiral Antenna

A numerical analysis is performed for a wideband two-arm Archimedean spiral antenna whose arms are made of vertical metallic strips. As such, the proposed antenna structure permits much tighter turns. An advantage of this spiral is that the input impedance and polarization purity can be effectively controlled by varying the strip width and turn thickness. Also, when the antenna is embedded in a dielectric block, miniaturization is more effective than in conventional planar Archimedean spirals.

An Integrated Dual-Band PIFA for DVB-T and WiMAX Applications

A compact dual-band planar inverted-F antenna (PIFA) working in the DVB-T (470-862 MHz) and WiMAX (3300-3800 MHz) frequency bands is presented. The antenna is designed to be integrated in a monitor-equipped device, like a television (TV) set, and meets strict space requirements. The final design fits a volume of 225 × 31× 20 mm3 (L×W ×H). It is composed of a series of branches, properly dimensioned and separated to generate the required resonances. A prototype has been realized with a 0.4-mm-thick aluminum foil, properly cut and folded. Results are shown in terms of reflection coefficient, radiation patterns, and gain. The antenna shows a reflection coefficient less then -6 and -10 dB, and a gain between 2.7 and 4.8 dBi and approximately equal to 3.7 dBi, in the DVB-T and WiMAX bands, respectively.

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.

Integration of Slot Antennas in Commercial Photovoltaic Panels for Stand-Alone Communication Systems

The integration of slot antennas in a class of commercial photovoltaic (PV) panels is addressed. The basic idea is to exploit the room available between adjacent solar cells, also taking advantage of the presence of the cover glass layer that gives a valuable miniaturization effect. As test cases, two antenna designs are presented for stand-alone communication systems operating in the GSM/UMTS (1710-2170 MHz) and WiMAX (3300-3800 MHz) frequency bands, respectively. At early design stage, antenna design has been performed by resorting to a simplified numerical model; afterwards, the effects on the antenna performance of nearby solar cells and DC bus wires have been numerically evaluated. The impedance tuning of the final antenna design has been carried out through a measurement campaign with slot antenna prototypes attached to real PV panels.

A square ring slot feeding technique for dual-polarized patch antennas

A novel slot fed dual-polarized patch antenna using a square ring slot and a single layer laminate for the feeding network has been presented. Numerical results have shown that the symmetry properties of the slot-patch pair allow us to obtain good performance in terms of isolation and amplitude of the cross-polar components. Measurements on prototypes will be shown at the conference.