This work presents the design, fabrication, and experimental validation of a complete near-field magnetic RFID system tailored for the detection of ultraminiature RFID chipless tags operating in the UHF range. The proposed system comprises four subwavelength-sized chipless RFID tags, a RFID reader and a backend detection system. The chipless tags are implemented as LC resonators consisting of an octagonal loop antenna and a floating capacitor that have areas of 17.89 mm2, 2.92 mm2, 1.65 mm2 and 0.75 mm2 and resonate at 1.21 GHz, 1.33 GHz, 1.29 GHz and 1.18 GHz, respectively. The RFID reader is a frequency-reconfigurable segmented loop antenna with an area of 122.54 mm2 that is controlled by voltage and operates between 1.14 GHz and 1.50 GHz. To evaluate the maximum detection distance at which each tag can be detected by the reader, a backend system based on the Frequency Sweep Envelope (FSE) method is applied to the phase derivative of both the reflection coefficient and the input impedance measured at the reader, in absence and presence of the different tags. The results demonstrate that combining the FSE method with the derivative of the input impedance phase provides higher sensitivity to the subtle perturbations introduced by the ultraminiature tags, enabling greater detection distances.

The mutual coupling between antennas is an important parameter in multi-antenna systems that needs to be controlled in order to ensure the performance of all involved components. While full-wave simulations are accurate in estimating the mutual coupling, they remain computationally expensive for large structures and are sometimes even impossible due to the lack of definition in early design stages of a system. This work summarizes the different coupling mechanisms between patch antennas and proposes a modified two-ray model technique in order to quickly estimate the mutual coupling. The proposed method is shown to agree well with full-wave simulations in the given scenarios and has the advantage of giving physical insight into the coupling mechanism especially with respect to polarization that then can be further utilized in developing methods to mitigate the mutual coupling.

This paper introduces a novel 2-D beam-steerable rectenna designed for mm-wave RF wireless power transfer (RF-WPT) applications. The 2-D beamsteering capability of the proposed rectenna is achieved by integrating an on-chip 4 x 4 Butler matrix, which is co-integrated with a rectifier array in a 22 nm FD-SOI CMOS, and a leaky wave antenna array. The proposed solution incorporates dual rectifier units simultaneously to enhance the receiver's power receptivity. In this manner, the rectenna is capable of receiving power from the same direction while taking advantage of frequency diversity. This is accomplished using the novel integration scheme of the single leaky wave array antenna with two rectifier units. The proposed solution maintains the system's compactness and reduces the overall cost while offering a fully passive 2-D beam scanning for the receiver unit. These merits make the proposed solution promising for RF-WPT applications in the Internet of Things (IoT) ecosystem.

This paper investigates a low-cost method to form a multibeam antenna with 2-D beamsteering capability. The simple feeding method employed in this solution enables the dielectric rod antennas to generate multiple beams in the intended direction simultaneously. In this manner, a multi-fixed-beam system is created without the need for a beamforming unit, which reduces the complexity of the final system architecture. Furthermore, a sensitivity analysis of the dielectric rod is performed, taking into account variations in critical design parameters and the permittivity of the rod. Different fabrication methods and low-loss materials that can be used for rod manufacturing are introduced, and the permittivity of these materials is characterized using the Nicolson-Ross-Weir (NRW) method. By doing so, our study not only presents a practical multibeam antenna formulation strategy but also reports appropriate materials and manufacturing processes that can be employed in the manufacturing of rod antennas.

This work presents a magnetic near field-based RFID system in which a miniaturized RFID chipless tag of 1.65 mm2 is detected by two RFID readers (#Reader 1 and #Reader 2) of different sensitivity. The two readers are 7.5x7.5 mm2 tunable segmented square loop antennas working in UHF band. However, #Reader 2 presents a better impedance matching and a finer frequency tunability than #Reader 1. Measurements were post-processed using frequency sweep envelope (FSE) method and the RFID chipless tag was detected at a maximum distance of 6.5 mm with #Reader 1 and at 11 mm in the case of #Reader 2. In this way, it is proved that a RFID reader with higher sensitivity in frequency and magnitude allows to detect RFID chipless tags at longer distances.

This paper presents a multibeam dielectric rod antenna for mm-wave wireless power transfer (WPT) applications. The proposed solution utilizes its unique multibeam setup which allows the generation of adjustable beams simultaneously, without the need for an additional beamforming network. To enhance the compactness of the system, each Rexolite rod is fed through an annular slot etched on a Rogers RO4003. The generated beams are steered toward the desired directions by adjustment in the configuration of these rods. The final configuration consists of five rods that were fabricated and measured. In this configuration, a beam coverage between $-30^{\circ}$ and 30 ∘ can be obtained, while in the frequency of interest, a gain value above $12\,\mathrm{dBi}$ is achieved. With its adjustable configuration, the proposed solution can be adapted to different operating scenarios. Moreover, the low cost and flexibility of the solution make it a promising candidate for Radio Frequency Wireless Power Transfer (RF-WPT) Internet of things applications.

This work presents some considerations for the use of a Split Ring Resonator (SRR) and its dual structure, the Complementary Split Ring Resonator (CSRR), as permittivity sensing elements. The analytical circuit equivalents of both resonators are reviewed in the light of multilayer transmission lines and adjusted models are derived for the resonant frequencies when superstrates with finite thickness are included, thus accounting for the finite thickness of the Material Under Test (MUT) and the possible use of a sample container with its corresponding material and thickness. Validations of the proposed analytical models are performed by means of full-wave electromagnetic simulation using a SRR loaded microstrip line and a CSRR loaded Substrate Integrated Waveguide (SIW), as dielectric permittivity sensors.

This paper introduces a beam-adjustable multibeam dielectric rod antenna for mm-wave RF-WPT applications. The unique multibeam setup allows the generation of several adjustable beams simultaneously. This is conceptualized by utilizing three and five rods to create a beam coverage between - 30° to 30° in the azimuth plane. In the proposed configuration, the peak gain value of each generated beam is 13 dBi at 23.8 GHz. A gain value above 12 dBi is maintained between 20 GHz and 24 GHz. The Rexolite rod is fed through an annular slot fabricated on a Rogers RO4003 substrate. The adjustable nature of this configuration makes the solution agile, with the possibility of adaptation to different scenarios either by altering the number of unit elements employed or their orientation. This capability, together with the low cost of the proposed solution, makes it a promising power delivery solution for Internet of Things (IoT).

One challenge in designing RF wireless bioelectronic devices is the impact of the interaction between electromagnetic waves and host body tissues on far-field wireless performance. In this article, we investigate a peculiar phenomenon of implantable RF wireless devices within a small-scale host body related to the deformation of the directivity pattern. Radiation measurements of subcutaneously implanted antennas within rodent cadavers show that the direction of maximum radiation is not always identical with the direction to the closest body-air interface, as one would expect in larger-scale host bodies. For an implanted antenna in the back of a mouse, we observed the maximum directivity in the ventral direction with 4.6 dB greater gain compared to the nearest body-air interface direction. Analytic analysis within small-scale spherical body phantoms identifies two main factors for these results: the limited absorption losses due to the small body size relative to the operating wavelength and the high permittivity of the biological tissues of the host body. Due to these effects, the entire body acts as a dielectric resonator antenna, leading to deformations of the directivity pattern. These results are confirmed with the practical example of a wirelessly powered 2.4-GHz optogenetic implant, demonstrating the significance of the judicious placement of external antennas to take advantage of the deformation of the implanted antenna pattern. These findings emphasize the importance of carefully designing implantable RF wireless devices based on their placements and relative electrical dimensions in small-scale animal models.

A series-fed loop antenna array, deployable by means of a scissors-type stretchable mechanism is presented. The antenna topology uses a continuous conductor with proper size to produce in-phase vertical currents that creates a highly directive pattern. The design methodology and simple guidelines for obtaining desired input impedance, gain and front-to-backlobe-ratio (FBR) are presented. A wire prototype was realized as proof of concept, demonstrating input impedance and radiation characteristics according to expectations.

This contribution presents an isotropic field probe to assess human exposition to broadband magnetic fields in the 400 MHz to 6 GHz band according to the ICNIRP 2020 guidelines. This device complements the current practice in this band, based on the measurement of electric field, which may underestimate the overall exposition in the near field of particular sources or scatterers. The design process accounts for the frequency response of all the system components involved. The performance of the isotropic configuration is assessed.

This contribution presents an isotropic magnetic field probe with shaped frequency response in the band 100 kHz - 400 MHz to ponder the aggregate response according to the ICNIRP 2020 guidelines. The basic sensor is a printed loop which is modelled as a Thévenin source obtained through full-wave simulation. A canonical filter is optimized considering the frequency response of the equivalent source, the detector and the desired transfer function. Finally, a cubic arrangement of three elementary sensors is used to assess the isotropy and isolation of the probe.

This contribution presents the design of a compact circularly polarized antenna featuring beamwidth reconfiguration in both the horizontal and vertical planes. The observed radiation patterns in each of the reconfigurable states present axial symmetry and circular polarization. The antenna is based on an arrangement of microstrip patches that can serve a dual purpose as a conventional array and as a fed central element with 4 parasitic elements. The reconfiguration is attained by switching the input signal towards either the parasitic or the conventional array. A particular design demonstrating a beamwidth reconfiguration in ∆θ 3dB ={38°,105°}, with circular polarization and axial symmetry is presented.

We present the design and validation of an isotropic field probe with geometry and frequency response shaped to correctly weight the aggregate contribution of the various frequency components of a broadband magnetic field in the band 100 kHz – 400 MHz according to the ICNIRP 2020 guidelines. The elementary sensor is a small strip loop printed on a thin dielectric substrate. The elementary sensor is initially analyzed via full-wave simulation from which a Thévenin equivalent model is extracted. Careful consideration of the frequency response of the loop and the power detector enabled the optimization of a canonical filtering topology to obtain the desired frequency response. Finally, the isotropic probe assembly consisting of a cubic arrangement of three elementary sensors is validated with respect to isotropy and isolation.

This paper presents a new process for additively manufacturing purely metallic antennas based on Fused Deposition Modeling (FDM), with a proprietary filament developed using a hot extrusion method and composed by a mix of rounded shape copper powders with particle sizes in the range from 20 to 80 mu m embedded in a polymeric matrix, to accomplish the desired antenna shape; followed by a post-processing stage involving de-binding to remove the base polymer and a further sintering process for obtaining a purely metallic component. This new process is validated by means of a prototype antenna consisting on a modified tri-band cactus monopole that is manufactured and measured, exhibiting results in agreement with standard and alternative additive manufacturing techniques reported in the literature.

In this paper, a novel feeding method for shorted annular ring (SAR) antennas is presented. SAR antennas can be designed to not excite surface waves and hence have desirable properties for many applications. The traditional method of feeding a SAR is through a single probe. Using two probes i.e. a differential feeding method, the current distribution and hence the pattern become more symmetric. However, steep current gradients on the patch make it difficult to obtain a robust design against manufacturing tolerances. A novel feeding method based on a dual aperture coupling approach is proposed to overcome the limitations of a dual-probe feeding approach while still maintaining the reduced surface wave characteristics. Additionally, this feeding method is shown to provide an increase in broadside gain of almost 3dB through eliminating disturbances in the current density on the SAR.

This contribution presents an approach to strengthen the internalization of theoretical concepts related to digital signal processing - DSP and communications systems by means of active learning using the GNUradio framework, highlighting the experimental work in the strengthening of learning Results show that user implemented blocks have capabilities comparable to the ones included in GNU radio library and the student's requested feeling of"real life" deployments, with the advantage of being flexible, software dependent, multipurpose hardware, which can be used in the laboratory for teaching and further research. On the other hand, significantly learned materials can be retained for a relatively long period of time, months, even years

The transformation of the automotive industry towards ubiquitous connection of vehicles with all kind of external agents (V2X) motivates the use of a wide range of frequencies for several applications. Millimeter-wave (mmWave) connectivity represents a paramount research field in which adequate geometries of antenna arrays must be provided to be integrated in modern vehicles, so 5G-V2X can be fully exploited in the Frequency Range 2 (FR2) band. This paper presents an approach to design mmWave vehicular multi-antenna systems with beamforming capabilities considering the practical limitations of their usage in real vehicular environments. The study considers both the influence of the vehicle itself at radiation pattern level and the impact of the urban traffic on physical layer parameters. Connectivity parameters such as Signal-to-Interference-plus-Noise Ratio (SINR) and outage probability are optimized based on the array topology. A shaped beam in the vertical plane based on three preset radiating elements is proven to be robust enough against self-scattering effects on the vehicle body. Regarding the horizontal geometry, four panels on the roof's edges provide good coverage and link quality. The number of horizontal antennas per panel tightly depends on the required values of the link quality metrics, potentially leading to a non-uniform geometry between sides and front or back panels.

Nonlinear effects in the radio front-end can degrade communication quality and system performance. In this paper we present a new design technique for reconfigurable antennas that minimizes the nonlinear distortion and maximizes power efficiency through the minimization of the coupling between the internal switching ports and the external feeding ports. As a nonlinear design and validation instance, we present the nonlinear characterization up to 50 GHz of a PIN diode commonly used as a switch for reconfigurable devices in the microwave band. Nonlinear models are extracted through X-parameter measurements supported by accurate calibration and de-embedding procedures. Nonlinear switch models are validated by S-parameter measurements in the low power signal regime and by harmonic measurements in the large-signal regime and are further used to predict the measured nonlinearities of a reconfigurable antenna. These models have the desired particularity of being integrated straightforwardly in the internal multi-port method formulation, which is used and extended to account for the power induced on the switching elements. A new figure of merit for the design of reconfigurable antennas is introduced-the power margin, that is, the power difference between the fed port and the switching elements, which combined with the nonlinear load models directly translates into nonlinearities and power-efficiency-related metrics. Therefore, beyond traditional antenna aspects such as port match, gain, and beam orientation, switch power criteria are included in the design methodology. Guidelines for the design of reconfigurable antennas and parasitic layers of minimum nonlinearity are provided as well as the inherent trade-offs. A particular antenna design suitable for 5G communications in the 3.5 GHz band is presented according to these guidelines, in which the specific switching states for a set of target performance metrics are obtained via a balancing of the available figures of merit with multi-objective separation criteria, which enables good control of the various design trade-offs. Average Error Vector Magnitude (EVM) and power efficiency improvement of 12 and 6 dB, respectively, are obtained with the application of this design approach. In summary, this paper introduces a new framework for the nonlinear modeling and design of reconfigurable antennas and provides a set of general-purpose tools applicable in cases beyond those used as examples and validation in this work. Additionally, the use of these models and guidelines is presented, demonstrating one of the most appealing advantages of the reconfigurable parasitic layer approach, their low nonlinearity.

In this letter, a reconfigurable dual-polarized broadband antenna with beam-steering capabilities using a parasitic layer is proposed for 5G new radio (NR) frequency range 1 (FR-1) applications. The antenna is a dual-port aperture-stacked patch structure with symmetrical orthogonal (horizontal and vertical) currents. The beam-steering is achieved by a pair of reconfigurable cross-shaped parasitic strips, which bestow the antenna three main beam directions theta = {similar to-25 degrees, 0 degrees, similar to 25 degrees}, phi = {0 degrees} with pointing and gain (7 dB) stability across a 30% impedance bandwidth (S-11, S-22 < -10 dB) from 3.2 - 4.3 GHz for both ports/polarizations. A prototype of the antenna is manufactured and measured demonstrating results in accordance with simulation expectations.