Abstract-An electrically small planar passive UHF-RFID tag based on an edge-coupled split ring resonator (EC-SRR) antenna is presented in this work. In order to explore the potentiality and limitations of the SRR antenna and to aid the tag design, an analytical study of the SRR radiation properties at its fundamental resonance is presented for the first time. Radiation resistance, efficiency, polarization, bandwidth and impedance matching with the RFID ASIC are treated in the study. Based on such analysis, the tag design process is presented, and a tag prototype of size 30 mm × 30 mm (λ 0 /11 × λ 0 /11) is designed to operate in the North-American UHF-RFID band (902−928 MHz) and manufactured. The measured read range is in good agreement with the simulation, and reaches 9.3 m at 911 MHz. The tag also features a mitigation of the blind spots, providing a minimum measured read range of 4.2 m.Index Terms -Split ring resonators (SRRs), electrically small antennas (ESAs), radio frequency identification (RFID).
Abstract-The radiation properties of split ring resonators (SRRs) at their second resonance frequency are studied for the first time in this work. In particular, the electric and magnetic dipole moments of the edge-coupled SRR (EC-SRR) are calculated analytically under the assumption of strong coupling between the internal and external rings. Based on these results, the radiation resistance and the radiation efficiency are obtained theoretically. Electromagnetic simulations of the structure reveal that there is very good agreement with the theoretical predictions, pointing out the validity of the proposed analysis. As a proof of concept, an SRR antenna prototype is designed and fabricated. Experimental data are in good agreement with the theoretical and simulated results, and demonstrate the validity of the SRR working at its second resonance frequency as a radiating element.Index Terms-Split ring resonators (SRRs), planar antennas, radiation efficiency, metamaterials.
A novel planar Yagi-Uda antenna is presented in this letter. The proposed antenna uses electrically small resonators as radiating elements that behave as short electric dipoles. Its radiation pattern, gain, front-to-back ratio (FBR) and efficiency are maintained close to that of a Yagi-Uda antenna of stacked half-wavelength dipoles. However, its physical dimensions are considerably reduced. The choice of the resonant particle and its radiation properties, along with the antenna structure, are discussed. Simulated results show a good impedance matching (29 dB) at the working frequency of 5.5 GHz for a 15-elements antenna, as well as a high gain (11.5 dBi). These characteristics are experimentally validated and compared with that of others Yagi-Uda designs from the literature.Index Terms-Electrically small resonators, end-fire array, front-to-back ratio, gain, planar Yagi-Uda antenna.
Abstract:The use of complementary split-ring resonators (CSRRs) as radiating elements in low-profile on-metal UHF-RFID tags is explored in this work. Firstly, the radiation properties of the edge-coupled (EC-CSRR) and the non-bianisotropic (NB-CSRR) versions of the CSRR are studied. The tag design strategy is then discussed in detail. On that basis, a compact (λ0/7 x λ0/7) low-profile (1.27 mm) tag prototype based on the NB-CSRR antenna is designed and manufactured to operate in the North-American UHF-RFID band. The experimental results validate the theoretical and simulated behaviour, and exhibit a maximum read range of 6.8 m.
The definition of a precise illumination region is essential in many applications where the electromagnetic field should be confined in some specific volume. By using conventional structures, it is difficult to achieve an adequate confinement distance (or volume) with negligible levels of radiation leakage beyond it. Although metamaterial structures and metasurfaces are well-known to provide high controllability of their electromagnetic properties, this feature has not yet been applied to solve this problem. We present a method of electromagnetic field confinement based on the generation of evanescent waves by means of metamaterial structures. With this method, the confinement volume can be controlled, namely, it is possible to define a large area with an intense field without radiation leakage. A prototype working in the microwave region has been implemented, and very good agreement between the measurements and the theoretical prediction of field distribution has been obtained.
In this work, the 2-turns Spiral Resonator (2-SR) is proposed as an electrically small antenna for passive radio frequency identification (RFID) tags at the European UltraHigh Frequency (UHF) band. The radiation properties are studied in order to explore the viability of the 2-SR applied to tag antenna design. Based on analytical calculations, the radiation pattern is found to provide a cancellation of the radiation nulls. This results in a mitigation of the blind spots in the read range, which are present in typical UHF-RFID tags as an undesired feature. As a proof of concept, a passive tag of size 35 mm x 40 mm (λ 0 /10 x λ 0 /9) based on the 2-SR antenna is designed and fabricated. Good radiation efficiency (75%) and a quasi-isotropic radiation pattern are obtained. The experimental tag read range for different directions is in good agreement with the simulation results. The measured read range exhibits maximum and minimum values of 6.7 m and 3.5 m, respectively.
The improvement of the front-to-back ratio (FBR) in low-profile antennas to be used in presence detection devices is explored in this work. The main idea is to use electrically small resonators as radiating elements. This minimizes the electric currents in the boundary of the ground plane at the working frequency, thus reducing the backward radiation. The choice of the resonant particle and its electromagnetic properties, along with the antenna structure, are discussed. The simulated results indicate that there is good impedance matching (−18 dB) at the operating frequency (3 GHz) and an excellent FBR of 24 dB. These characteristics are validated experimentally and the FBR is compared to that of a conventional patch antenna.Introduction: Most modern buildings incorporate automatic presence detectors for security, energy saving and domotics. These devices usually integrate infrared or ultrasonic sensors and hence they are unable to detect objects through walls, floors or ceilings. This fact restricts the operational region of the detector to the room where it is placed. To overcome this difficulty, presence detectors operating at microwaves have been proposed. These devices use a microwave signal transmitted by an antenna, which is reflected back by the target to be detected. Since the functionality of these microwave detectors can be extended over several meters, it is important to restrict the sensing region to avoid undesired readings. The most important parameter that quantifies this problem is the front-to-back ratio (FBR) of the emitter antenna, defined as the ratio of the power sent in the direction of detection over the power sent in the opposite direction. Thus, the FBR must be maximized for an adequate performance.Low cost microwave detectors usually incorporate common planar microstrip antennas, consisting of a rectangular metal patch placed on top of a dielectric substrate mounted over a large ground plane. This type of antennas is supposed to provide a radiation diagram located in the half-space due to the presence of the ground plane. Nevertheless, since this kind of antennas can be viewed as an open circuited transmission line, the electric field at the edges of the conductor patch will spread into the surrounding substrate. This results in the extension of currents over a significant area of the ground plane. For this reason, the ground plane should be maintained electrically large, in order to preserve the radiation diagram and hence minimizing the radiation to the back side of the antenna. However, in some applications, the size of the antenna is a critical issue and should be minimized. To overcome this drawback, we propose the use of an electrically small resonator, which concentrates the currents around its geometry, as a radiator. Considering that the particle is relatively close to the ground plane (and also its image, located on the opposite side of the ground plane [1]), the induced currents in the ground plane are expected to be concentrated in a relative small region around the resonato...
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