Abstract in English:Abstract In an elastic network paradigm, where the transceiver is able to control several characteristics of the transmitted signal according to the optical link quality and capacity demand, receivers able to automatically detect the modulation format are fundamental to recover the transmitted signal without the necessity of headers that reduce system capacity. This work presents a simulated performance comparison of six methods for blind identification of modulation format in high-capacity optical systems: k-nearest neighbors (KNN), k-means, fuzzy c-means, deep neural networks, support-vector machine (SVM) and peak-to-average power ratio (PAPR). The transmitted channels were 64-GBd modulated with the following modulation formats available at the transceiver: QPSK, 16QAM, 64QAM, and 256QAM. The optical link was emulated considering several impairments, as amplified spontaneous emission from optical amplifiers, frequency and phase noise from lasers, and polarization rotation and differential group delay from the propagation. The support-vector machine algorithm presented the most robust results.
Abstract in English:Abstract In this paper, a new methodology is applied to optimize the geometry of conductors of overhead transmission lines (TL) with high precision and low computational cost. This methodology is based on the sensitivity analysis of the electrical charge of the transmission lines using the adjoint method. This information is used with the gradient method and the golden section algorithm to minimize the electric field at the ground level of three-phase TL with two cables per phase. The approximation using central finite differences to obtain sensitivity is adopted for validation and comparisons. The TL's with high surge impedance loading is obtained after the optimization process.
Abstract in English:Abstract A reconfigurable frequency selective surface, FSS, associating cross dipoles and matryoshka geometries is described in this paper. The proposed reconfigurable FSS uses as active element PIN diodes. With the associated geometries, three resonant frequencies are achieved, two fixed, related to the matryoshka geometry, and one that can be activated or not, related to the cross dipoles geometry. Differently from previous works, an inductor was inserted into the cross dipoles’ horizontal arms, maintaining its resonance for x polarization. The PIN diode inserted into cross dipoles’ vertical arms controls the respective resonance. The design procedures for each geometry, in addition to PIN diode and RF inductor basics are outlined. The expected results are discussed based on the analysis of the resonances of each geometry and the associated geometries, as well as the different PIN diode bias states (OFF and ON). A prototype was fabricated and characterized, obtaining a good agreement between the numerical and experimental results, with a reconfiguration bandwidth of 0.24 GHz, from 2.12 GHz to 2.36 GHz, for a variation of at least 10 dB between the OFF and ON states.
Abstract in English:Abstract The present work describes the use of a simulation model based on asymptotic methods (ray tracing) on the propagation of ultra-wideband radio signals in a densely-arborized urban channel. The model was previously validated and adjusted using data obtained from measurement campaigns in the millimeter-wave band in locations different from the one to be analyzed here. The simulation uses deterministic methods to predict the received power, cross-polar discrimination, root mean square delay spread, and mean delay in a channel with a high density of scatterers (trees, buildings, and poles). Simulated signals were transmitted in the vertical and horizontal polarizations, considering non-specular reflections caused by rough surfaces and the effect of the transmitter’s height variation in outdoor channels.
Abstract in English:Abstract This paper addresses the influence of the primary and secondary resistances on the behavior of minor hysteresis loops when the electromagnetic device is fed by three-level PWM (pulse width modulation) voltage. To study the device transferring energy to a load, the experimental approaches are different of traditional procedures to material characterization, where problems inherent to the process are added. Analytical, FEM and experimental analysis are performed on a toroidal transformer equipped with a flux sensing coil. The leakage fluxes related to the primary and secondary currents are shown to cause errors in the measurement of the core magnetization current. A solution to mitigate this problem is employed, consisting in twisting and winding together primary and secondary conductors. Experimental methodologies for obtaining the value of the iron losses when the device is transferring energy to a load are also performed. The study shown showed that supply voltage with three-level PWM waveform causes minor hysteresis loops and the greater the resistance value of the excitation winding, the larger the areas of the minor hysteresis loops. On the other hand, by increasing the energy transferring to a load the minor loops areas tend to decrease.
Abstract in English:Abstract In this work we propose a new method to separate iron losses by removing low frequency tests and reducing the number of experiments. The article deals with methodologies that use numerical methods to find the mathematical model coefficients of magnetic loss separation in hysteresis loss (Wh), eddy current loss (Wed) and excess loss (Wex). Three methodologies are presented and depend on experimental tests such as (i) varying magnetic induction Bm and constant supply frequency (f) of 50 Hz, (ii) constant magnetic induction around 1 T and varying frequency. The first methodology is based on Newton’s method to solve the numerical system generated with experimental data from two laboratory experiments. These data were reported in past references. Another two methodologies are based on genetic algorithms (GA). One of them depends on experimental data from both experiments and the another depends on experimental data only from experiment (i). Results indicate that genetic algorithms method presents excellent solutions in comparison with other ones. The GA method with two tests allows a better representation of the experimental behavior of the sample with maximum errors varying from 1.10% to 0.20%. In GA method with one test, minimization varied from 6.924 × 10−05 to 3.186 × 10−05.
Abstract in English:Abstract This paper presents an Antipodal Vivaldi Antenna (AVA) design, focusing on its constructional aspects. The main features analysed are the connector attachment structure and the introduction of a polytetrafluoroethylene (PTFE) part that supports the antenna laminate. Issues related to dielectric penetration by milling tools are also addressed. The proposed AVA was manufactured through a low-cost prototyping process and tested, achieving an operational bandwidth from 5 to 18 GHz for a reflection coefficient less than −10 dB and an average gain of 6.23 dBi. The prototype meets all design requirements, which shows the viability of the developed radiator.
Abstract in English:Abstract The optimization of three-dimensional device has widely been explored and designated as computational challenge in photonic device design. In this context, this work presents a novel multi-symmetric level (MSL) optimization procedure based on Genetic Algorithm (GA) to decrease the computational requirements in a three-dimensional photonic coupler device optimization. The proposed procedure divides the device optimization into many local regions by dimensional symmetric aspects, being based on divide- to-conquer strategies. As the optimization converges to acceptance values, the number of symmetric areas are decreasing until a unique local area that modeled the total 3D photonic device. This procedure was validated by the minimization of a photonic coupler modeled to interconnect optical waveguides with different height, width and refractive indices.
Abstract in English:Abstract The software-defined radio has been allowing engineers the possibility of implementing operations on software that were previously only possible to be performed through hardware. With the continuous increase in the processing capacity of computers, it is possible to modify in real time the operating parameters of new radios called Software Defined Radios (SDR) or use commercial devices for other purposes, in addition to those established in their design. By using a low-cost device RTL-SDR R820T2, controlled by a Raspberry Pi 3, with a free software, the present work proposes a characterization procedure in order to collect power levels measurements in a given frequency range with greater accuracy, acting as a spectrum analyzer. Preliminary measures were performed with the device embarked on a drone.
Abstract in English:Abstract Radio-Frequency Identification (RFID) is one of the leading enabling technologies of the Internet of Things (IoT) at low cost and high granularity scenarios. The cost of implementing IoT applications concerns the development and operation of receiver systems for reading labels. In this paper, we propose a low-cost receiver system based on off-the-shelf components allied to the development of a microstrip antenna. The proposed system is capable of receiving and processing digital signals scattered back from a passive RFID tag. The proposal relies on a Python application embedded in Raspberry Pi hardware, in which a bank of digital filters processes the signal. The proposal separates the received signal into sub-bands and implements a decision-maker that detects and codes radiofrequency carriers’ presence in sub-bands. Simulation using artificial random noise proves that the proposed and implemented decision-maker achieves 92% reliability for a Signal-to-Noise ratio between 1.6 dB and 2.3 dB. The evaluation of the printed dipole antennas pair for the RFID receiver system indicates a return loss of 19.22 dB for operation at 915 MHz.
Abstract in English:Abstract The electro-optical bandwidth and extinction ratio requirements of in-phase and quadrature modulators to enable 1 Tb/s per channel optical transmission rates are evaluated through numerical simulations. Employing sixty-four quadrature amplitude modulation (64QAM), the simulation results indicate that the best trade-off between the number of optical carriers per channel and the technological complexity of designing and manufacturing an integrated transceiver is achieved for a superchannel composed by 2 optical carriers, since it allows modulator requirements in terms of electro-optical bandwidth and extinction ratio equal to 27 GHz and 18 dB, respectively. The systemic optimization of the carrier launch power employing the approximate enhanced Gaussian noise model indicates that this configuration could achieve transmission reaches up to around 1080 km. These results point out to 1 Tb/s optical superchannels as a viable solution for next generation coherent systems in metropolitan and long-haul scenarios.
Abstract in English:Abstract This paper presents a compact and planar reconfigurable filtenna for application in Wireless systems. The filtenna is composed of a UWB circular antenna and a filter with two trapezoidal resonators. The filter is integrated on the antenna feed line and has a band-pass frequency response. The filtenna frequency response reconfiguration is achieved by changing the capacitance of a varactor diode, placed between filter resonators; the capacitance varies continuously from 1.32 pF to 4.09 pF according to an applied bias voltage. The varactor capacitance analog variation defines the filtenna frequency of operation, which can be varied from 2.2 GHz to 3.4 GHz with an average bandwidth of 200 MHz, while maintaining the radiation characteristics of the UWB antenna. Simulated and measured filtenna results are shown according to varactor diode bias, demonstrating multiband operation using a compact planar design.
Abstract in English:Abstract In this paper, a broad band A-sandwich radome wall structure based on band-pass FSS (frequency selective surface) is proposed for an airborne radar applications. The FSS structure having two square conducting rings, which are embedded on either side of core layer. The conventional and proposed FSS based radome wall is analyzed with different incidence angles (0°, 10°, 20° and 30°) for both TE and TM polarization. The radome wall structure consist of a low density Nomex honeycomb core layer sandwiched between two high density Quartz skin layers. The structure shows the percentage impedance bandwidth of 40.8 % in the frequency range from 7.8GHz to 11.8GHz with sharp roll-off characteristics. The proposed novel approach involves high frequency unit cell simulation, which is carried out using EM Simulation Tool. To understand the practical behavior of the proposed structure for radome application the conformal analysis has been also carried out, with respect to different radius. The superior EM performance of the proposed broadband novel radome wall structure makes it suitable for the design of airborne radome.
Abstract in English:Abstract This work presents improvements to a telecommunication service planning tool for optimal positioning of base stations presented in a previous work. The tool uses a propagation loss model based on the K-Nearest Neighborhoods classifier since its conception. The original objective of this tool is to optimize the positioning of transmitting towers in the frequencies of 2.1 GHz and 2.6 GHz in a given environment, maximizing the coverage area. The improvement proposed in this article includes the optimization of the positioning of the towers in order to meet the maximum coverage, prioritizing the locations considered most important. The studied scenario is the campus of the Federal University of Pará, with characteristics similar to some cities in the Amazon region. The analysis of the results was made by comparing the power data received from the measurement campaigns with the coverage estimates obtained with the improved tool. The improved methodology showed better results than those from the previous study, both in the positioning of the antennas and in the time spent. We obtained a reduction of up to 72% in the time to calculate the optimal solution compared to the original study.
Abstract in English:Abstract The development of new mathematical model for guide polarization converter with diaphragms was carried out in the research by the method of wave matrices. In addition, numerical modeling of the performance of a polarizer with diaphragms is made by simulating the propagation of the fundamental modes with perpendicular linear polarizations. The wave matrix model was obtained by splitting the polarizer into separate structural elements. Each element was described by its own wave transmission matrices. As a result, a general wave scattering matrix was formed. Based on the elements this matrix the electromagnetic characteristics of the considered polarizer were obtained theoretically. In particular, complex reflection and transmission coefficients were calculated. Their modules and phases were analyzed in the frequency interval 10.7-12.8 GHz. To check the correctness of the obtained results an independent numerical simulation was carried out applying the finite element methodology in the frequency interval. The results of both approaches are in good agreement. The engineered converter of polarization with four diaphragms provides a reflection coefficient modulus of less than 0.14 and a transfer coefficient modulus of more than 0.99 for two orthogonal types of polarizations. As a result, a rigorous mathematical method was developed to analyze the elements of the scattering matrix of a waveguide polarizer with diaphragms. It can be used for the development of new broadband waveguide polarizers and waveguide filters based on diaphragm elements.