Carla R. Medeiros

Performance of a Crossed Exponentially Tapered Slot Antenna for UWB Systems

A compact printed antenna is described that exhibits adequate transient performance for ultrawideband (UWB) applications and it is further adequate for polarization diversity schemes. The antenna is based on an original combination of two crossed exponentially tapered slots plus a star-shaped slot to produce a stable radiation pattern with very stable polarization over the 3.1-10.6 GHz FCC assigned band. Results are confirmed with measurements. Figures of merit like output pulse fidelity and time window containing 90% of the transmitted energy are analyzed over the entire solid angle and showed to remain quite stable, in line with envisaged UWB system requirements. Compact dual-antenna arrangements are also analyzed in view of potential use for UWB multiple-input-multiple-output implementations.

RFID Smart Shelf With Confined Detection Volume at UHF

This letter presents a smart shelf configuration for radio frequency identification (RFID) application. The proposed shelf has an embedded leaking microstrip transmission line with extended ground plane. This structure, when connected to an RFID reader, allows detecting tagged objects in close proximity with proper field confinement to avoid undesired reading of neighboring shelves. The working frequency band covers simultaneously the three world assigned RFID subbands at ultrahigh frequency (UHF). The concept is explored by full-wave simulations and it is validated with thorough experimental tests.

RFID Reader Antennas for Tag Detection in Self-Confined Volumes at UHF

Confinement of the detection region is a critical issue for some important RFID applications, where the coarse location of the object is required along with its identification. In the UHF band, it is a challenge to confine antenna radiation to reasonably sharp interrogation volumes, <; 10λ3, without resorting to physical barriers. This paper presents a novel approach for RFID reader radiating structures that self-confine tag detection to a desired volume, avoiding undesired readings outside the interrogation volume. The proposed solution simultaneously covers the three world-assigned RFID frequency subbands at UHF. To demonstrate the effectiveness of the solution, the proposed configuration was integrated into bookshelves, a conveyor belt system, and a proximity point reader. Together with an appropriate control application, these form the building blocks of a smart store with automatic inventorying and billing capability. The radiating structure concept was explored by full-wave simulations, and it was validated with both near-field measurements and with tag-reading scores. Short demonstration videos are available online.

Compact Tapered Slot UWB Antenna With WLAN Band Rejection

This letter extends the design of a previously proposed uniplanar ultrawideband (UWB) antenna to include within its 3.110.6-GHz operation band a rejection of the wireless local area network (WLAN) band near 5.5 GHz. The antenna configuration is based on a combination of two crossed exponentially tapered slots plus a star-shaped slot printed on both sides of a 10-mils dielectric substrate. The band rejection is obtained with the addition of extra slots at the antenna back-face metallization. The radiation pattern and polarization are very stable over the entire UWB. Link measurements between two identical antennas demonstrate low pulse distortion over almost all the solid angle.

Wideband Slot Antenna for WLAN Access Points

This letter presents a new printed slot antenna with cavity back for wireless local area network (WLAN) access points (base stations) providing wideband operation bandwidth at least from 2.5 to 4.8 GHz. The design is based upon an ultrawideband (UWB) antenna configuration modified with the inclusion of a cavity back in order to produce stable unidirectional radiation pattern. The new configuration also ensures a stable linear polarization with cross-polarization level below -20 dB. Results are confirmed with measurements. Not disregarding other applications, the new design is especially adequate for multiple-input-multiple-output (MIMO) space and polarization diversity arrangements, presenting low cross polarization and very low coupling to adjacent elements.

Evaluation of a New Wideband Slot Array for MIMO Performance Enhancement in Indoor WLANs

A new wideband compact slot antenna array for indoor WLAN access points (AP) is described, covering several wireless communication services from 2.4 to 4.8 GHz, that is especially designed to enhance MIMO system capacity. The array topology provides both spatial and polarization diversity. Despite very close packing of the array elements, these exhibit very low mutual coupling and low cross-polarization, greatly favoring MIMO diversity gain. A detailed MIMO performance comparison is conducted against a common array of patches in indoor environment, based both on simulation and indoor measurements: the new antenna shows a clear improvement in terms of channel capacity.

Passive UHF RFID Tag for Airport Suitcase Tracking and Identification

A passive UHF tag configuration is presented for suitcase identification and tracking in airport-handling applications. The proposed tag antenna solution is based on a conformal geometry, consisting of a folded dipole with orthogonal arms, appropriate for integration into the wall of injection-molded suit- cases during its fabrication process. The tag antenna is designed for the ALIEN Higgs-2 integrated circuit. Simulated frequency dependence of the proposed UHF passive tag shows adequate performance across the world UHF RFID bands. Maximum tag detection range as well as detection isotropy were measured in several test environments both for a prototype tag attached to a suitcase and for a tag embedded in the suitcase wall. Full detection of the embedded tag was obtained for all suitcase orientations in the tested scenarios.

Mirror-Integrated Transparent Antenna for RFID Application

An optically transparent antenna array is presented for radio frequency identification (RFID) systems, operating in the ultrahigh frequency (UHF) band. The antenna is intended for nonintrusive integration into the mirror surface of fitting rooms in apparel stores, keeping with the typical small depth of the mirror structure and low cost. The antenna is used to read RFID tags attached to clothes being tried on, so that the associated system can automatically provide the client with interactive information regarding that specific piece of clothing. The antenna ensures self-confined reading range in front of the mirror, avoiding undesired detection of RFID tags from adjacent fitting rooms. The final antenna solution shows a good compromise between transparency and performance, with well-confined RFID detection volume.

UHF RFID smart conveyor belt with confined detection range

Radio Frequency Identification (RFID) technology enables detection and recognition of objects associated to univocal identification codes. A typical RFID system comprises an RFID reader linked to one or several antennas that interrogate the tags within its detection range. A dedicated computer application manages the data logging and processing. Several frequency bands are assigned to RFID, from HF up to microwaves. At present, the UHF RFID tags are preferred for a wide range of applications because its unit cost is the lowest. The usable UHF band ranges from 860MHz to 960MHz, allocated in three different intervals for different world regions by the International Telecommunications Union (ITU).

Experimental demonstration of a structured material with extreme effective parameters at microwaves

Following our recent theoretical studies [M. G. Silveirinha and C. A. Fernandes, Phys. Rev. B 78, 033108 (2008)], it is experimentally verified that an array of crossed metallic wires may behave as a nonresonant material with extremely large index of refraction at microwaves and may enable the realization of ultrasubwavelength waveguides.Following our recent theoretical studies [M. G. Silveirinha and C. A. Fernandes, Phys. Rev. B 78, 033108 (2008)], it is experimentally verified that an array of crossed metallic wires may behave as a nonresonant material with extremely large index of refraction at microwaves and may enable the realization of ultrasubwavelength waveguides.