Resumen en Inglés:

Abstract In this paper, a novel broadband high-selectivity stacked filtering antenna with multiple radiation nulls is proposed. The antenna consists of a short-circuited stepped impedance feeding line and two U-shaped strips on the bottom layer, four parasitic patches and a rectangular driven patch etched with two Г-shaped slots on the top layer. Short-circuited stepped impedance feeding line and Г-shaped slots respectively introduce two radiation nulls, which greatly improves low-band edge selectivity. Two U-shaped strips and four parasitic patches respectively introduce two radiation nulls, effectively increasing the upper stopband rejection level. For demonstration, one prototype of the filtering antenna with a center frequency of 2.4 GHz is fabricated and measured. Measurement results manifest that the impedance bandwidth is 15.8% (from 2.18 to 2.56 GHz) with the antenna gain of 7.69 dBi. Furthermore, four radiation nulls can be generated at 1.91, 2.01, 2.60, and 2.72 GHz, respectively. And the lowerand upper-edge selectivities are 157.3 and 310.9 dB/GHz, respectively.

Resumen en Inglés:

Abstract This work presents the generation and analysis of beam matrices and Bessel-Gauss beams, integer and fractional, using holographic techniques. Experimental optical beam generation was performed using computer-generated holograms (CGHs) and spatial light modulators (SLMs). Also, a digital holographic interferometry technique was also used to characterize the intensity and phase profiles of these beams. The theoretical and experimental results are in agreement and show how the Bessel-Gauss beams, integer and fractional, propagate along the optical axis, in addition to the transverse intensity and phase profiles. In addition, Bessel- Gauss beam matrices were generated experimentally with results that were consistent with the theoretical simulation. These results are very promising, with excellent possibilities to expand the applications of these beams and matrices in different areas, such as optical manipulation, optical metrology, optical communications, and quantum information, among others.

Resumen en Inglés:

Abstract This study proposes a low-cost microwave sensor for the monitoring of water quality contamination in irrigation systems. The sensor was employed for monitoring the concentration of specific compounds in mixtures of glucose and water, in order to prevent the accumulation of unwanted sugars in large plantations. The proposed sensor is an adaptation of a complementary split ring resonator (CSRR) fabricated on an FR4 substrate. A capillary tube constructed from polypropylene is inserted into the region of the CSRR microwave sensor exhibiting the maximum density surface current, wherein the liquid under test (LUT) is contained. The sensor was designed to operate at a resonance frequency of 2.45 GHz in the absence of a load. The maximum displacement observed at the resonance frequency is 275 MHz, with a normalization sensitivity of 0.844%. The simulations and experimental measurements are verified and their results compared, yielding a high level of concordance for the sensor’s intended purpose. The discrepancy between the measured permittivity values and the reference values of the samples under analysis is less than 5%. The proposed sensor is an effective solution for characterizing liquids, particularly mixtures of water and glucose, when compared to other sensors available for this application

Resumen en Inglés:

Abstract In this article, a new Meander-Bridge Electromagnetic Band-Gap Structure was proposed for the suppression of Simultaneously Switching Noises (SSN) over a wide frequency range, with dimensions of 15 x 15 mm and a useful area of 100 mm2. The equivalent model of the structure was created using lumped elements along with transmission lines. This method allowed determining the response characteristics across the entire frequency range of interest. Two boards were fabricated for conducting all the tests, including near-field and far-field measurements, S-parameter measurements, and electromagnetic wave simulations. The performance achieved a -30 dB level between the two ports in the frequency range of 1.75 to 11 GHz. To verify signal integrity, tests were conducted using ADS software at different communication rates, along with an internal near-field analysis of the PCB. Farfield measurements were also conducted experimentally. All the tests confirm the effectiveness of the proposed structure, demonstrating attenuation of SSN noise over a wide frequency band.

Resumen en Inglés:

Abstract This article presents the design of a top-loaded quartercylinder dielectric resonator antenna (TL-QCDRA). The approach to reduce the antenna dimensions is based on the use of E and H-walls to impose Dirichlet and Neumann boundary conditions to the fields inside the dielectric resonator. The proposed antenna was modeled and optimized with the electromagnetic simulator ANSYS HFSS and was designed to operate at 1.575 GHz (L1- band of the global positioning system - GPS). The excitation is achieved by a coaxial probe along with a series inductor, whichis used to compensate the capacitive input reactance. A prototype was manufactured and measured in an anechoic chamber and good agreement was obtained between numerical and experimental results. In comparison to previously published papers, the proposed design yields higher compactness, which is an important feature for space applications.

Resumen en Inglés:

Abstract This article explores the performance of a Yagi-Uda patch antenna with Koch fractal geometry of different orders on an FR-4 substrate. It exhibits multiband operation, enabling the use across multiple frequency bands. The proposed reflector features equally spaced slots. The radiating dipole element has a Koch fractal geometry of order 2, while the third directive element of the antenna is shaped as a Koch fractal of order 1. The antenna was designed and simulated using CST Studio® from 1 GHz to 10 GHz. After fabrication, measurements with a vector network analyzer (VNA) verified the presence of 11 operational bands with resonance frequencies centered at 1.265 GHz, 1.545 GHz 2.59 GHz, 2.7 GHz, 3.05 GHz, 3.9 GHz, 5 GHz, 5.18 GHz, 5.71 GHz, 6.20 GHz, and 8.72 GHz. It results in an aggregate bandwidth of 652 MHz (Ultra-Wideband, UWB) with applications in a range of protocols and technologies. The antenna dimensions are only 100 mm x 120 mm, resulting in a compact size.

Resumen en Inglés:

Abstract This article describes a two-element antenna designed in a Digital Terrestrial Television Broadcasting (DTTB) Multiple Input Multiple Output (MIMO) 2×2 front antenna in the 470 to 700 MHz band. It is based on a planar, canonical, fat-dipole element with low-cost and robust characteristics. Both antenna elements are fed directly by a coaxial connector, without a balun, and have been optimized to provide low coupling, improving their combined diversity gain. The array occupies an area of 0.76λ2o x 0.51λ2o (907 cm2) at the center frequency wavelength. Measurements of the antennas in outdoor urban environments are presented with a technology proponent for the project, the Advanced Integrated Services Digital Broadcasting - Terrestrial (ISDB-T), in 8 urban sites in Rio de Janeiro, Brazil. The results showed that the proposed MIMO 2×2 antenna operates effectively in outdoor applications, is robust, has a low development cost, and has a low degree of mutual coupling.

Resumen en Inglés:

Abstract This research provides detailed examination of the peak spatial Specific Absorption Rate (psSAR) in different age students in a classroom with wireless computers. This is motivated by the escalating inclusion of electronic devices in educational settings and the necessity to estimate the implications of this on the overall radio-frequency exposure. Two classrooms with posable realistic human models are simulated. One filled with several 7 years old children and another with several 43 years old adult, each using a laptop. The 1 g and 10 g psSAR are calculated for the head, back and hands. The distances between students are varied and the results compared to one student alone. A small free distance between rows (10 cm) produces significant reduction in psSAR (around 13 dB). Results are less sensitives to changes in lateral distance. While the maximum simulated psSAR values are below the recommended limits, it is observed that, in some classroom arrangements, the psSAR can be substantially increased (e.g., up to 26 dB in the back) comparing to just one student with his laptop. One objective of this study is to provide guidelines for the design of safer classrooms in the context of widespread laptop usage.

Resumen en Inglés:

Abstract Recently, many machine learning techniques have been presented to detect brain lesions or determine brain lesion types using microwave data. However, there are limited studies analyzing the location of the lesions through machine learning approaches, despite the critical importance of lesion localization for treatment. This paper contributes to the literature on microwave brain lesion localization by comparing several machine learning algorithms rather than proposing a single algorithm. In the proposed approach, lesions of varying sizes and locations are randomly embedded into realistic 2D brain models. The brain models are divided into four regions, each representing the possible location of the lesion. Subsequently, training and test datasets are generated by computing the electromagnetic fields scattered from healthy brains and brains with lesions via the Method of Moments. Each sample in the datasets is labeled as healthy, region 1, region 2, region 3, or region 4 according to the presence and location of the lesion. Finally, we developed models using various classifiers and compared their effectiveness. Among these, the models trained with stochastic gradient descent classifier, ridge classifier, and logistic regression demonstrated notable accuracy (91%, 82%, and 77%, respectively) for both detection and localization of lesions.

Resumen en Inglés:

Abstract In this study, a rib waveguide is used in the design of a plasmonic sensor. The structure consists of a dielectric substrate constituted of tantalum pentoxide (Ta2O5). On top of this substrate, a superstrate with a ridge, composed of niobium pentoxide (Nb2O5), is overlayed forming the guiding region. A thin sheet of graphene is placed over the Nb2O5 and below the analysis region, where concentrations of dimethyl sulfoxide (DMSO) ranging from 50% to 100% will be detected. The purpose of incorporating the graphene sheet is to induce the effect of localized surface plasmon resonance (LSPR), which in this configuration becomes sensitive to variations in the refractive index (RI) of DMSO. The surface plasmons in graphene (graphene-SP) are induced by collective oscillations of charge carriers, i.e., free electrons in graphene, which, when subjected to specific frequencies, couple with the electromagnetic fields at the interface between graphene and the dielectric. The basic principle is similar to that of surface plasmons in noble metals,however, surface plasmons in graphene can occur at lower frequencies. With this configuration, a plasmonic sensor is obtained to detect DMSO concentrations, designed for a wavelength of 0.6329 micrometers.

Resumen en Inglés:

Abstract Small Remotely Piloted Aircrafts (RPAs) are gaining an increasingly prominent role in society. However, their growing use has raised concerns due to their potential misuse for illicit activities. Consequently, the detection and accurate classification of small RPAs have become crucial. Conventional radar systems, however, struggle to distinguish these aircraft from birds, as their Radar Cross-Sections (RCS) are very similar. To address this challenge, the Micro-Doppler (MD) effect has emerged as a valuable tool, enabling the differentiation of signals between birds and small RPAs. It also facilitates the classification of these aircraft. This study analyzed the Micro-Doppler (MD) effect generated by the motion of the rotating components of quadcopter RPAs and explored how this phenomenon can be utilized to extract information, such as rotor rotation speeds and propeller sizes, for an initial classification of these aircraft. Furthermore, the MD effect produced by birds was examined to identify characteristics that can be used to differentiate RPAs from birds. Lastly, the results of MD effect measurements using a Frequency-Modulated Continuous Wave (FMCW) radar during the RPA FIMI X8 SE flight were analyzed and discussed.

Resumen en Inglés:

Abstract This paper presents a fully textile band-stop frequency selective surface (FSS) designed with a central frequency of 3.6 GHz and a bandwidth of 190 MHz. The structure, composed of two semicircles connected by a central line, was designed, fabricated, and experimentally validated. The prototype was created using copper ink on a pure cotton fabric substrate and tested in the laboratory for incident angles and polarizations ranging from 0° to 45°. Additionally, the structure’s performance was examined under two different curvatures. All simulated and experimental results are provided and analyzed.

Resumen en Inglés:

Abstract Wider bandwidth microstrip antenna employing resonant slot require substrate thickness in excess of 0.07λg, which increases the antenna volume. In this paper, a novel technique to increase the bandwidth in E-shape microstrip antenna fabricated on a thinner microwave substrate, while employing printed resonator elements is proposed. The printed resonator positioned below the patch, introduces TM20 mode nearer to the TM10 mode in E-shape antenna that increases the bandwidth. On substrate thickness of 0.037λg, optimum design achieves bandwidth of 130 MHz (13.89%), with a broadside radiation pattern and peak gain of 7.8 dBi. With the obtained antenna characteristics, proposed thinner substrate designs will find applications in GSM band.