Scielo RSS <![CDATA[Journal of Microwaves, Optoelectronics and Electromagnetic Applications]]> http://www.scielo.br/rss.php?pid=2179-107420180001&lang=en vol. 17 num. 1 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[Performance Analysis of Probe-Fed Circularly-Polarized Moderately-Thick Microstrip Antennas Designed under the Null Reactance Condition]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100001&lng=en&nrm=iso&tlng=en Abstract This work presents a performance analysis of probe-fed circularly-polarized moderately-thick microstrip patch antennas. Five typical geometries are designed according to the null reactance condition. A nonlinear regression, based on HFSS simulations, is implemented in order to identify the most robust geometry, regarding the manufacturing process. The analysis focus is on broadside axial ratio degradation and frequency deviation parameters. Experimental results validate the proposed approach and the nonlinear regression calculations. <![CDATA[A Hybrid Approach for Assessments of Equivalent Emission Sources and Electromagnetic Environments]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100010&lng=en&nrm=iso&tlng=en Abstract This paper presents a method for equivalent emission source determination by application of LLAs (Large Loop Antennas). A review of different types of LLAs is carried out and their characteristics regarding emission source evaluation are emphasized. A hybrid technic is applied for obtaining the electric fields based on previous measurement of magnetic fields combined with an analytical and numerical approach. This methodology is proposed as an alternative to face the constraints concerning to the near electric fields measurements and calculations. <![CDATA[Microstrip Hybrid Coupler with a Wide Stop-Band Using Symmetric Structure for Wireless Applications]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100023&lng=en&nrm=iso&tlng=en Abstract In this paper, a wide stop-band microstrip coupler is presented. The proposed structure consists of coupled lines and step impedance cells, which are integrated to operate at 2.82 GHz for wireless applications. This coupler is formed by a symmetric structure so that the locations of the output ports relative to input are quite similar. Accordingly, the magnitudes (also phases) of S21 and S31 overlap each other so that input signal can be selected through the output ports equally. There are little differences between the magnitudes and phases of S21 and S31 so that 0.97° phase shift is obtained. In comparison with previous works, the performance of the introduced coupler is improved. To get a better isolation, return loss and harmonic attenuation the frequency response is optimized without significant increase in circuit size. Moreover, the first, second and third harmonics of S21 and S31 are well attenuated as well as a wide stop-band is obtained up to 15.1 GHz. The realized coupler is fabricated and measured. There is a good agreement between simulated and measured results, which confirms the design process. <![CDATA[Analysis of the Propagation Properties of 90°-bend Periodic Segmented Waveguides Using the 2D Finite Element Method]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100032&lng=en&nrm=iso&tlng=en Abstract We use the two dimensional finite element method (2D-FEM) in the frequency domain to characterize the transmission properties of 90°-bend periodic segmented waveguides (PSWs). We investigated the dependence of the transmission coefficient and the mode profile of PSWs on the bending radius, the waveguide duty cycle, and the operating wavelength. We show that 90°-bend PSWs can be designed in photonic integrated circuits with a curvature radius as small as three times the wavelength to achieve transmission coefficient greater than 0.8. <![CDATA[Extremely high Faraday and Kerr rotations and extraordinary optical transmission in four-layer dielectric-metal strips-dielectric-Bi:YIG planar structure]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100044&lng=en&nrm=iso&tlng=en Abstract Faraday and Kerr effects as well as the extraordinary optical transmission in a structure that combines magneto-optical and plasmonic properties are studied. The planar structure consists of four layers, namely, dielectric layer, metal strips, once again dieletric layer and magneto-optic one. The magneto-optical layer is magnetized by a DC magnetic field normal to it. Our numerical analysis shows that the Faraday and Kerr rotations in this structure can be increased by more than two times in comparison with the published results. This is achieved due to high Q-factor resonances in magneto-optic layer. <![CDATA[Polarization Insensitive Compact Wide Stop-band Frequency Selective Surface]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100053&lng=en&nrm=iso&tlng=en Abstract A compact, polarization insensitive, wide stop band frequency selective surface is presented. The unit cell is designed by modifying the basic square loop FSS. The simulated value of bandwidth for transmission &lt; ‒ 20 dB for TE incident wave is 7.7 GHz from 4.71 GHz to 12.41 GHz which is 89.95% corresponding to the center frequency of this range. It has an excellent band stop response for C and X band. The periodicity of the unit cell is the order of 0.33λ0 at the center frequency of 8.56 GHz. The total thickness of the proposed structure is 1.6mm (0.045λ0). Standard design formulas are used to evaluate the resonance frequencies and calculated values are found to be very close to the simulated ones. The proposed design is polarization insensitive and has good angular stability. An array of the proposed design is fabricated on either side of dielectric substrate FR4. The measured and simulated transmission responses are in good agreement. Proposed design can be used for many potential applications such as electromagnetic shielding, spatial filtering, sub - reflector in antennas and RCS reduction etc. <![CDATA[Adaptive Modulation and Code Strategy to Reduce Energy Consumption in Elastic Optical Network]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100065&lng=en&nrm=iso&tlng=en Abstract In this paper, the novel Adaptive Modulation and Code (AMC) algorithm aims to reduce energy consumption in elastic optical network is developed. The proposed AMC algorithm adaptively allocates both, the appropriate modulation and the forward error correction (FEC), according to the actual physical distance and the optical signal to noise ratio (OSNR) of the lightpath, respectively. The algorithm compares the previous energy consumption with the actual aiming to select the lowest. The obtained results have been compared with the case when shortest path (SP) and minimum hops (MH) algorithms are employed. Simulations outcomes highlight that energy consumption decreases when AMC algorithm is adopted in comparison with SP or MH ones. The energy consumption increases proportionally with the physical lightpath distance. Finally, the blocking probability decreases whereas AMC is utilized. <![CDATA[Use of a combined SVD-Kalman filter approach for induction motor broken rotor bars identification]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100085&lng=en&nrm=iso&tlng=en Abstract This paper describes a new parametric spectral estimator for the identification of rotor bar fault of an induction motor by analyzing the stator current. This approach combines two methods: The first one, the Singular Value Decomposition method which allows the accurate detection and location of the fault's signature frequency. The second method allows the estimation of the fault amplitude. To this end, the Kalman filter is used for its efficient estimation of both amplitude and phase using the frequencies obtained by the first method. This combination of both methods gives a better frequency resolution for a very short acquisition time, which cannot be obtained using the conventional method of the Periodogram. Moreover, in order to reduce the significant computation time resulting from the use of the Kalman filter, the proposed approach is applied only to the frequency band where the fault signature is likely to appear. A series of tests will be carried out on real signals representing rotor faults. <![CDATA[Characterization of Switchable Rectangular Ring FSS with Non Coupled Parallel Metallic Strips for Multi Band and Dual Polarized Applications Using WCIP Method]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100102&lng=en&nrm=iso&tlng=en Abstract In this paper, a rectangular metallic ring FSS (Frequency Selective Surfaces) with parallel metallic strips for multi band applications are characterized by the WCIP (Wave Concept Iterative Procedure) method. The proposed FSS structures are made of metallic elements that are simultaneously independent in the spatial domain and uncoupled in the spectral domain. Thus the FSS multiband behavior can be achieved only by a building process based on independent metallic elements in both domains. The resonant characteristics of the proposed FSS are determined. The structure shows three resonant frequencies when the incident wave is x-polarized and three resonant frequencies when the source is polarized in the orthogonal direction. A variation in the length of the strips and the rectangular ring allows a fine tuning in the FSS resonant frequencies to give raise to tuned bandwidths. The suppression of a resonant frequency can be insured either by the elimination of the responsible metallic strip or by the insertion of a PIN diode switch. Three FSS structures are manufactured and characterized. The FSS bandwidth can be enhanced in both perpendicular FSS exciting source directions by only varying the strips lengths and the ring dimensions to the corresponding resonant frequencies. A good agreement is obtained when the WCIP results are compared with the simulations of COMSOL Multiphysics software and experiment. <![CDATA[Analytical Approach for Making Multilayer and Inhomogeneous Structures Invisible Based on Mantle Cloak]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100121&lng=en&nrm=iso&tlng=en Abstract We investigate an analytical approach based on transmission line model to design mantle cloak for multilayer and/or inhomogeneous dielectric objects. Our proposed model is verified with different numerical results. The results matched well with each other. Also, the required impedance for making an inhomogeneous material invisible is calculated analytically. Finally, some complex structures are implemented using CST simulator and suitable performance is reached. So, it is proved that mantle cloak is applicable for making complex inhomogeneous materials invisible. <![CDATA[Sharp Rejection and Wide Stopband Microstrip Lowpass Filters using Complementary Split Ring Resonators]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100134&lng=en&nrm=iso&tlng=en Abstract Chebyshev microstrip lowpass filters with improved performance, achieved by means of circular complementary split ring resonators (CSRR), are presented. CSRR particles exhibit frequency rejection bandwidths in the vicinity of their resonant frequencies that can be used to meliorate both selectivity and stopband in microstrip lowpass filters. Two configurations have been used: a stepped-impedance model and a configuration using open-circuited stubs. Microstrip filters having 5, 7 and 9 poles were designed and fabricated. Selectivity values up to 86 dB/GHz and suppression levels reaching 60 dB in the stopband were obtained. The filters have cutoff frequency around 2 GHz and rejection band up to 10 GHz. The insertion of the designed CSRR resonators in the ground plane of the filters removes all the transmission spurious observed in the analyzed frequency band. No considerable variation in the passband group delay is observed in the CSRR-based lowpass filters. A comparison is made among the filters designed in this and other referenced works, considering their number of poles and size. The measured results are in good agreement with the simulated ones. The presented filters can be candidates for applications using the VHF, UHF and L bands, being also very effective in the rejection of the S and C bands. Applications that demand the rejection of the first half of the X band can also use the filters detailed in this paper. <![CDATA[Novel Design of Photonic Digital Sensors for Distinguishing Uniformly-Distributed Refractive Indices of Fluids]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100144&lng=en&nrm=iso&tlng=en Abstract The authors propose a novel structure of k-level (k is an arbitrary integer) photonic digital sensor based on directional couplers with specific structural parameters. Its function is similar to an analog-to-digital converter (ADC) in electronic system, and capable of distinguishing 2k+1-1 discrete and uniformly-distributed refractive indices of the fluidic samples. In this paper, the principle of designing the photonic digital sensor is described, and the beam propagation method (BPM) simulation results are presented for demonstrating the validity of our design. <![CDATA[Dual-Port Dual-Wideband Annular Slot Antenna with Stable Unidirectional Pattern]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100156&lng=en&nrm=iso&tlng=en Abstract This article describes the design of a dual-wideband annular slot antenna. The proposed structure has been optimized to operate in the typical bands of mobile communication systems (0.824-0.960 GHz and 1.710-2.165 GHz). The antenna is designed considering two independent ports with high isolation, one for each operation band, yielding an antenna that exhibits diplexing feature. The final measured results show that the designed antenna exhibits stable radiation pattern over the frequency in both desired bands. The designed antenna has been used to compose a dual-band linear array. Simulation results indicate good performance in both bands for mobile communication systems. <![CDATA[Millimeter Wave Antenna for Intelligent Transportation Systems Application]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100171&lng=en&nrm=iso&tlng=en Abstract A compact broadband millimeter wave antenna for intelligent transportation (ITS) application is proposed in this paper. This antenna uses coplanar wave guide feeding technique for broad bandwidth. The proposed antenna works at 79 GHz resonant frequency having a large bandwidth of 78.2 GHz. The measured gain of the antenna is 17.5 dBi. The proposed antenna is very suitable for short range radar (SRR) application and %G technologies. <![CDATA[Propagation Model for Path Loss Through Vegetated Environments at 700 – 800 MHz Band]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742018000100179&lng=en&nrm=iso&tlng=en Abstract In almost all literature about propagation models through vegetated environments, path loss has been proposed based on specimens of temperate clime conditions. In this work, a new propagation model is proposed, based on measurements, carried out on vegetated environments with tropical specimens. These environments are common on suburban and rural areas in Brazil. Current models have presented pessimistic approach to propagation loss in these areas. The vegetal morphology and frequency effects, transmission height and distance are taken into consideration. Finally a comparison with existing models is presented.