Scielo RSS <![CDATA[Journal of Microwaves, Optoelectronics and Electromagnetic Applications]]> vol. 16 num. 1 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[Indoor Characterization of Power Delay Profile Using Equivalent Antenna Representation in Uniform FDTD Lattices]]> Abstract It is shown that proper representation of transmitting and receiving antennas in indoor environments are decisive for accurate prediction of electromagnetic power transfer parameters using the standard 3D-FDTD method. With the standard Yee method, it is not always possible to precisely describe all the geometrical details of electrically small antennas. A new approach for description of the discone antenna in uniform 3D-FDTD lattice is presented. The calculations are validated by comparing FDTD results with the polyhedral beam-tracing method and experimental data. <![CDATA[Rigorous Analysis of a Compact Triangular Antenna Array Using the Spectral Domain Method]]> Abstract The main objective of this work is the characterization of triangular array antenna with circular form by using the spectral domain technique. Firstly, the spectral domain formulation of single triangular patch antenna is given, in order to calculate its resonant frequencies and its radiation patterns. Then, we calculate and plot the total radiated field which is the multiplication of a single element radiation by the array factor, when patches are made in a circular arrangement. Comparing to the exiting array antenna design, the numerical results, obtained from the implementation of our calculations, have shown that the networking increases the gain, improves the directivity and controls the bandwidth with a compact form of the antenna arrangement. In addition the effects of different parameters of the structure on its performances are presented. <![CDATA[A Compact UWB Bandpass Filter using Hybrid Fractal Shaped DGS]]> Abstract In this paper, a novel and compact ultra wideband (UWB) bandpass filter (BPF) based on fractal-shaped defected ground structure (DGS) is designed and developed. It is made of stepped impedance lines and a composite right/left handed-transmission line (CRLH-TL) constructed with capacitive gap in conductor strip and a hybrid fractal-shaped ring slot in ground plane. The capacitive gap between conductor strip and fractal shaped DGS play the major role for controlling the lower and upper passband cutoff frequencies. The prototype of proposed filter is fabricated and measured. Good agreement is found between simulated and measured results. The proposed UWB bandpass filter has good passband performance with 10 dB return-loss bandwidth of 2.2 to 10.6 GHz, insertion loss better than 1.1 dB and fractional bandwidth of 131%. Also, the proposed filter obtained a very wide upper-stopband from 11.4 GHz to beyond 20 GHz with rejection skirt better than 30 dB at both the lower and upper passband cutoff frequencies. Moreover, UWB BPF also shows the flat group delay performance with variation ≤ 0.75 ns in the entire passband. Thus the proposed filter can be a useful candidate for low profile future wireless communication systems. <![CDATA[Ku-band Transition with not Metalized Air-Vias between Microstrip Line and Substrate Integrated Waveguide]]> Abstract In this letter, a new transition between microstrip line and substrate integrated waveguide in Ku-band frequency is proposed. This transition composed of one row of not metallized air-vias drilled on both sides of the microstrip line with taper end. The electromagnetic analysis is carried out using a commercial software tool. The presented transition achieves return losses better than 41 dB in Ku-band frequency (12.4–18GHz). In order to validate the simulated results of the proposed concept, a back-to-back transition prototype is designed, fabricated and measured. The measured results demonstrate a minimum return loss of 29.05 dB and maximum insertion loss of 0.685 dB over the entire Ku-band frequency. <![CDATA[A low-profile and ultra-wideband printed antenna with a 176% bandwidth]]> Abstract This work reports the development of a simple, low-profile and ultra-wideband printed antenna. The proposed antenna is based on a truncated ground plane and an impedance matching structure formed by a round junction and two chamfers; these modifications significantly increase the antenna frequency bandwidth compared to conventional microstrip antennas and ultra-wideband printed monopoles published in literature. An antenna prototype was fabricated using an Arlon DiClad 880 substrate with an electrical permittivity of 2.2. A bandwidth of 176% was attained at a central frequency of 14.9 GHz (ranging from 1.79 to 28.02 GHz). Numerical simulations and experimental results of the antenna's radiation pattern are also reported and exhibit good agreement. To the best of our knowledge, this is the widest bandwidth from a printed antenna that has been published in the literature. <![CDATA[Non-invasive monitoring system of synchronous generator using external field]]> Abstract This paper presents an equipment dedicated to the monitoring of synchronous generator through the measurements of the external magnetic field time derivative. The equipment uses a methodology which can be an additional technique to those applied currently on the faults detection, mainly when monitoring the incipient faults type. Based on frequency spectra (magnetic signatures), the faults detection is performed by the analysis of the components evolution. As it is not possible to test the ability of the equipment in detecting several types of faults of generators faults in a power plant, a testbench was constructed for this purpose. Faults inserted deliberately in the generators of the testbench are detected by the equipment, showing its capacity. This equipment has been also installed in power plants. <![CDATA[Estimation of Three-Phase Induction Motor Equivalent Circuit Parameters from Manufacturer Catalog Data]]> Abstract The single phase equivalent circuit is largely used to model the three-phase induction motors in steady-state operation and under sinusoidal balanced voltages. Depending on the desired application, the circuit may or may not represent core losses, a double cage or even the variation of parameters due to skin effect and saturation. However, the determination of the circuit parameters through standard methods, such as those described in IEEE Standard 112, may not be possible in many situations given the lack of the necessary resources. This paper presents initially a survey on the determination of circuit parameters from alternative methods, i.e., non-standard tests. Special focus is given to methods which employ only data usually provided by manufacturers on catalogs and nameplates. Six analytical methodologies used in the context of efficiency estimation at steady-state operation are assessed, compared and then combined in order to improve results. The assessment is based on the closeness of the resulting parameter values to reference values and on the inexistence of absurd results, such as negative electrical resistances. The combination of methods has improved the accuracy of calculations for the studied motors. <![CDATA[Magnetic Gearing Electromagnetic Concepts]]> Abstract In this paper the magnetic geared machines electromagnetic concepts are introduced. The magnetic gear modulation mechanism which becomes possible rotors of different polarities produce torque is explained, through the use analytical expressions and plots obtained by finite elements method. This pedagogical approach is a way to teach the subject in a more understandable way and, at the same time, it reinforces the application of electromagnetic concepts. Further, a magnetic geared generator is simulated and no-load EMFs and torques are analyzed. <![CDATA[Computational Modeling of Geoelectrical Soundings using PML-FDTD]]> Abstract The Finite-Difference Time-Domain (FDTD) method was applied in order to analyze the transient responses of geoelectrical soundings that use circular electric dipole (CED) as source over stratified formations. The model was developed in cylindrical coordinates and a perfectly matched layer (PML) was incorporated to the domain to absorb wave reflections at computational grid boundaries. Numeric results are validated with analytic solutions. Comparisons between the transient response of two different type of soundings are performed and results indicate that the transient response of soundings that excite purely TM mode are more sensitive to the variation of electrical characteristics of the medium. <![CDATA[Development of an Analytical Method to Predict the Behaviour of the Magnetic Field in PM Linear Motors with Halbach Array]]> Abstract This paper describes the application of the method of separation of variables and the use of Fourier series for solving the Laplace's and Poisson's equations on the study and analysis of the magnetic field produced in a linear motor with Halbach array. Equations for predicting the 2D magnetic flux density distribution produced in the air gap were developed. The model was validated by means of finite element analysis and by measurements carried on a prototype of the linear motor. Theoretical results helped understand the behaviour of the magnetic flux density in the air gap and to obtain the values of the static propulsion force and normal force in such machine. <![CDATA[Impact Analysis of PM magnetization level on motor performance: simulations and experimental results]]> Abstract This paper addresses the impact of magnetization level tolerances in ferrite-based permanent magnets (PM) on the performance of brushless DC motors. A case study is prepared using three motor prototypes assembled with controlled samples of ferrite arc segments, in terms of magnetization. The investigation is performed both experimentally and through simulations using the software SPEED. The results show that narrow tolerance margins for the magnetization conditions in the production line can potentially minimize the use of raw material on such motors whereas keeping the efficiency and torque behavior required by the application. <![CDATA[An Improved Method for Acquisition of the Parameters of Jiles-Atherton Hysteresis Scalar Model Using Integral Calculus]]> Abstract An accurate modeling of materials is essential to obtain reliable results in fields calculation. The Jiles-Atherton approach is widely used for modeling the magnetic hysteresis and depends on its set of five parameters to properly represent material. In this article is proposed an original methodology for obtaining this set of parameters avoiding the derivatives rough calculation and using the calculation of integrals. From the model equations, a new methodology with two nonlinear algebraic systems of five equations in five unknowns is obtained. The initial magnetization curve, the anhysteretic curve and filtering data are not necessary. The proposed methodology also does not restrict the search space of parameters. The parameters assume values in the interval (0,∞). Calculated data were compared with experimental data to validate the methodology. The simulations showed that the proposed method can obtain an accurate set of parameters from a single experimental hysteresis loop and with low computational effort. <![CDATA[Design of a Blade Antenna Embedded in Low-Cost Dielectric Substrate]]> Abstract A design of a blade antenna embedded in low-cost dielectric substrate (FR4) and operating at 4.97 GHz is the subject of this paper. The antenna design is accomplished using parametric analysis in the HFSS™ software, where the antenna dimensions are changed and it is observed how the changes affect figures-of-merit like input impedance, reflection coefficient and radiation patterns. The antenna prototype is presented, as well as, a comparison between experimental and theoretical results. <![CDATA[EDFA Design and Analysis for WDM Optical Systems Based on Modal Multiplexing]]> Abstract Modal multiplexing (MDM) is a core technology to allow a capacity increase in modern optical systems. However, in MDM links, the amplified WDM signal suffers not only from lack of spectral gain equalization but also from unequal modal gain. The proper design of the MDM-EDFA is crucial to provide modal gain equalization and to overcome those impairments, thereby ensuring long haul transmission. In this paper, our methodology of project EDFA design for MDM-WDM systems is presented. The technique is based on a figure of merit arising from the rate and propagation equations which describe the EDFA behavior. This figure of merit is then used for the definition of the objective functions employed in the optimization step, which is based on the non-dominated sorting genetic algorithm NSGA-II. Finally, the method is applied to demonstrate gain equalization through the simulation of a WDM optical system composed of two group modes (LP01,s and LP11,s) with up to 16 channels in each mode. It is demonstrated that, for a MDM-WDM system with optimized EDFAs, the differential spectral gain is the main cause of non-equalization of the amplified signal. <![CDATA[Optically controlled reconfigurable antenna for 5G future broadband cellular communication networks]]> Abstract This paper presents an optically controlled reconfigurable antenna for millimetre-wave frequency range. Silicon switches are used to control the optical reconfiguration, modifying the frequency response and radiation pattern of the antenna design. Therefore, the system can switch between the lightly licensed 28 GHz and 38 GHz frequency bands, useful for future mobile 5G broadband cellular communication networks. Experimental results with the reconfigurable antenna on 16-QAM and 32-QAM wireless transmission supported by photonic downconversion are successfully reported under 78 dB link budget requirement. <![CDATA[Electromagnetic Characterization of Aircraft Composite Materials and its Effects on the Antenna Performance]]> Abstract This paper presents an electromagnetic characterization of aircraft composite materials, as well as numerical and experimental analyses of its effects on the antenna performance. Two uncalibrated S-parameters characterization methods have been applied for retrieving the complex electrical permittivity in the L- and C-band, namely: Air-region method and Sample-shifted method. Dielectric constants of 4.6 and 1.84 and loss tangent of 2.0×10−2 and 6.1×10−2 have been obtained for fiberglass and honeycomb composite materials, respectively. A 3.0-meters prototype of an Embraer light jet aircraft dorsal fin was fabricated and used in the experiments in a semi-anechoic chamber in order to evaluate the impact of installing aeronautical VHF and L-band antennas on a fuselage made of composite materials. <![CDATA[An Analytical Solution for Fiber Optic Links with Photonic-Assisted Millimeter Wave Upconversion Due to MZM Nonlinearities]]> Abstract Photonic-assisted technique employed in the generation of stable and high-purity signals in the millimeter wave band has been investigated using dual-parallel Mach-Zehnder modulator. Indeed, this type of generation performs a high order RF multiplier, whose operation principle steams out from the nonlinear characteristic of the external modulators. Its application in direct-detection fiber optic link was investigated based on an exact formulation that properly takes into account both the dispersion of a single mode fiber and the modulator nonlinearity. Analytic expression for the link transfer function dependence with respect to both modulator bias point and modulation index were obtained. It is worthwhile to mention that RF tuning is enabled since no optical filtering is required. As an illustration of the modeling usefulness, it is analytically shown that a 60 GHz millimeter signal, generated by photonic quadruplicating a 15 GHz signal using dual-parallel Mach-Zehnder modulator, can be transmitted through a 80 km link of standard single mode fiber with less than 0.1 dB deviation with respect to ideal flat response. This performance is much better than previously published results. <![CDATA[Analysis of Parameters for a Distributed Temperature Sensing based on Raman Scattering]]> Abstract This paper presents a theoretical and computational study on the analysis of parameters for distributed temperature sensing in optical fibers, based on spontaneous Raman scattering effect. The parameters studied were the optical power level, the range of frequency modulation and the length of the sensor element, as well as the application of optical frequency domain reflectometry (OFDR). Two different approaches of reading temperature information from the backscattered signal were also tested. First, one considered the pulse response, and later the ratio between the amplitudes of the detected signals were taken. Such analysis has shown the second method is more efficient to detect the peak of hot spot temperature in the fiber. Spatial resolution equal to 0.96 m and a temperature resolution of 0.089 °C were achieved using singlemode fiber 30 meters long. <![CDATA[Polarization Diversity on ESM Systems]]> Abstract Polarization diversity antenna arrays are applied to electronic support measures (ESM) systems since the 1980s. However, even today modern systems are conceived with the employment of the traditional and inconvenient spiral antennas and there are no studies that evidences most of the benefits of this technique applied to them. This paper aims at showing not only the advantages on polarization matching issues, but also the benefits in gain, in simpler truncation effect problems and in costs and time spent on design and production. After a brief approach strictly applied to ESM of the main features of spiral antennas and bow-tie antennas compounding a polarization diversity array, equations of the power available from the last were developed from the concept of effective length. The results demonstrate that the array could provide a power 8.7 dB higher than a modern spiral would to an ESM system when it receives vertical or horizontal linearly polarized waves, which multiplies by 2.7 the range of the system, besides also presenting a better performance in case of circularly polarized incident waves. This work has contributed to propose a replacement to the very common use of spiral antennas on the upcoming ESM system projects. This study is recommended for the areas of Electronic Warfare, Electromagnetic Devices and Applications and Ultra-Wideband Antennas. <![CDATA[Pseudo-Analytical Modeling of Tilted-Coil Antennas in Anisotropic Geophysical Formations]]> Abstract In this paper we present an efficient mode-matching technique to analyze tilted-coil antennas in anisotropic geophysical formations. In this problem, a number of coil antennas with arbitrary relative tilt angle with respect to the symmetry axis are used to radiate electromagnetic fields in a cylindrically layered medium comprised of a metallic mandrel, a borehole, and a surrounding layered Earth formation. This configuration corresponds to that of directional well-logging tools used in oil and gas exploration. Our technique combines closed-form solutions for the Maxwell's Equations in uniaxially anisotropic and radially-stratified cylindrical coordinates with the generalized scattering matrix (GSM) at each axial discontinuity based on the modematching technique. The field from the transmitter tilted-coil source is represented by a set of modal coefficients which, after computation using GSM matrices, are used to compute the transimpedances. We present validation results which show that our technique can efficiently model directional well-logging tools used for oil and gas exploration. <![CDATA[Non-resonant Permittivity Measurement Methods]]> Abstract The measurement of the dielectric properties of materials has been applied in non-destructive tests, humidity measurement, soil analysis and even cancer detection. The methods have been developed for over 70 years based on the interaction of the electromagnetic waves with the material under test. This work presents a general model of scattering parameters for non-resonant methods of transmission/reflection and single-port reflection. Equations for determining permittivity are obtained. New equations for short-circuited load and coupled load in the double reflection method are presented. <![CDATA[Parametric Study of Printed Monopole Antenna Bioinspired on the Inga Marginata Leaves for UWB Applications]]> Abstract A microstrip leaf-shaped printed monopole antenna bioinspired on the Inga marginata leaves is presented in this paper for UWB applications. A parametric study of the proposed antenna bioinspired geometry was conducted in order to verify their resonant properties. The antenna was designed with a rectangular slitted ground plane for impedance matching and fabricated on inexpensive glass fiber substrate and fed by a 50 Ω microstrip line. Numerical and experimental results were obtained. The results show an impedance bandwidth superior to 10.26 GHz, greater than the bandwidth considered UWB (7.5 GHz). Antenna dimensions were optimized with the computer program Ansys Designer® used to simulate the electromagnetic behavior of the antennas by the method of moments.