Scielo RSS <![CDATA[Journal of Microwaves, Optoelectronics and Electromagnetic Applications]]> vol. 17 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Comparison of FDTD and TDWP Methods for Simulating Electromagnetic Wave Propagation above Terrains]]> Abstract Researchers have always been in face of path loss calculation in different media for applications such as telecommunication link design. Wave propagation calculations in large spaces using the FDTD method is time-consuming and imposes a great computational burden. For this reason, to replace the classical FDTD method for wave propagation simulation and path loss calculation in large spaces, optimized methods, namely TDWP, have been provided. In this paper, the use of the TDWP method for wave propagation simulation and path loss calculation above a terrain is investigated. Longitudinal components of ground-waves are taken into account (including direct waves, ground reflections, and surface waves). Propagation space is longitudinally divided into smaller FDTD windows with finite length. The electromagnetic pulse travels through these windows from left to right to the desired point. But despite its capability in reducing computational burden and increasing processing speed, TDWP has lower precision in instantaneous field simulation and calculation of propagation coefficients, so that results obtained from FDTD and TDWP are clearly different. In this paper, some efficient methods are proposed, which yield an increase in method accuracy. <![CDATA[Multiband FSS Analysis and Synthesis Based on Parallel Non Coupled Metallic Strips Using WCIP Method]]> Abstract A novel parallel non coupled metallic strips frequency selective surface (FSS) is presented. The design is based on a filter composed of horizontal and vertical metallic strips. The structure has the advantage of simplicity and gives multi resonant frequencies easily controlled by a simple variation in the strips length. The proposed FSS rejects frequencies at 7GHz, 9.4GHz with bandwidths of 0.646GHz, 0.793GHz respectively when the structure is excited with an x polarized plane wave, and two frequencies at 9.1GHz and 11.2 GHz with bandwidth of 280.3MHz, 63MHz respectively when the structure is excited with a y polarized plane wave. To suppress frequencies ideal diode on reverse bias are inserted. The simulated results obtained using WCIP (Wave Concept Iterative Method) are compared to the COMSOL Multiphysics 4.3b software results, and measurements, a good agreement is observed. Then, an FSS synthesis approach based on non coupled parallel metallic strips is presented. It provides synthesized FSS with resonant frequencies ranging from 4.5GHz and 12.25 GHz for metallic strips lengths inversely varying from 5mm to 19mm. To validate the synthesis approach, measured resonant frequencies are used as desired resonant frequencies to determine the metallic strips lengths. As a result the metallic strips FSS dimensions are extracted. At this stage the WCIP method is used to characterize the synthesized FSS. Three FSSs are synthesized based on the fabricated FSS and good agreement between measurements and synthesized FSSs results is recorded. <![CDATA[WCIP Method Applied To Modeling an L-Notched Rectangular Metallic Ring FSS for Multiband Applications and its Equivalent Structure]]> Abstract A frequency selective surface (FSS) with a unit cell containing of an L-notched rectangular metallic ring pattern that can be adopted for dual polarization applications is proposed and analyzed using the wave concept iterative procedure (WCIP). The parametric study of the FSS provides three FSS dimensions where their variation independently or simultaneously results in resonant frequencies tuning. They are the two dimensions of the L part of the FSS and its notch penetration and changing their values in the FSS allowed intervals gives rise to charts and equations based on polynomials determined by the use of least mean square method. Thus no need to software to determine the FSS resonant frequencies once the application is restricted to a specific FSS such as the L- notched rectangular metallic ring FSS for low cost FSS use. The presented synthesis approach is extended to the determination of the equivalent FSS structures based on non-coupled parallel metallic strips for the complex FSS structures of difficult comprehensive resonance sources. One FSS is manufactured and characterized. A good agreement is recorded when the WCIP results for the transmission coefficient are compared with the results of COMSOL Multiphysics software and measurement. <![CDATA[Improvements Evaluation of High-Speed Electro-Optical Integrated Thin-Film Microwave Coupler SOA-based Space Switch]]> Abstract The speed and transient improvements due to a thin- film microwave coupler on a high-speed SOA-based space switch are analyzed. The switch performance is compared with another one using the same SOA device but in its commercial butterfly encapsulated form factor. Through an extensive experimental characterization and an automated algorithm analysis, the switching actions were evaluated in several SOA operational conditions (bias current, electrical pulse step amplitude, preimpulse amplitude, and switching technique) employing metrics related to the switching times and transient behavior intensity. The results showed that the thin-film coupler SOA switch mounting led to switching time improvements and quicker optical output pulse stabilization. In conjunction with the appropriated switching technique, the device could achieve switching speeds around 200 ps aiming its operation in high-speed optical networks. <![CDATA[Validation of RKAS Soil Dielectric Model at C and X-Band Microwave Frequencies]]> Abstract In the present study an attempt is made to validate soil dielectric model which was formed to estimate the values of dielectric constant of dry and moist soil at various volumetric moisture contents at C and X-Band microwave frequencies. Eight Soil samples are collected from various parts of Haryana. Dielectric constants are measured using waveguide cell technique at C and X-Band microwave frequencies at varying volumetric moisture contents and then compared with estimated values obtained from model. The model has good accuracy and practicality. <![CDATA[Improved Polynomial Rooting of Capon's Algorithm to Estimate the Direction-of-Arrival in Smart Array Antenna]]> Abstract Direction of arrival algorithms are used, in general, to estimate a number of incident plane waves on the antenna array and their angles of incidence. In this paper, firstly, a new approach representing a more extensive version of the conventional Capon method is proposed. The study employs the root-Capon approach based on cross-correlation matrix in extracting the estimated direction-of-arrival of some number of signals to a given uniform linear array (ULA) antenna system. Secondly, a simple modification on the antenna element's number is employed for the Capon and the proposed approach to obtain more performances. The effectiveness of the proposed algorithm is verified through numerical simulation examples, and it is shown that the root version of Capon method can provide more accurate angle estimation with less computational complexity than conventional Capon algorithm. Similarly, it is found also that the used modification plays a significant role in the performance's improvement of Capon and its variant approaches. <![CDATA[Parametric study and Analysis of Band Stop Characteristics for a Compact UWB Antenna with Tri-band notches]]> Abstract In this article, equivalent circuit modeling with study and analysis of band notch characteristics for a triple band notched UWB antenna has been discussed to develop a better understanding of the antenna functioning and its behavior. A small square ultra wideband antenna having overall size of 24 × 31 mm2 with tri- band rejections is designed and simulated using HFSS software. Very narrow band notching is accomplished by placing C slots and inverted C slot of different dimensions on the radiating patch which makes maximum space utilization without performance deterioration. The antenna operates from 3.1 to 14 GHz (VSWR &lt; 2) with the presence of 3 narrow band notches (VSWR &gt;2) of 3.3-3.7 GHz (WiMAX), 5.1 – 5.4 GHz (Lower WLAN and HIPERLAN/2) and 5.7 − 6 GHz (Upper WLAN) as shown by the simulated and measured results (VSWR&lt;2) of the UWB antenna, with and without the presence of triple notches, thus utilizing the maximum UWB bandwidth. The radiation pattern plots for simulated and measured results are also presented to validate the working of the antenna. This antenna can be a respectable candidate for future European and USA high capacity UWB applications. The group delay and peak gain plots are also found to be stable in the range of operation of the antenna. The study and analysis of the band notching is discoursed in terms of current distribution and impedance plots to provide a greater and better perception into the working of the antenna and hence an equivalent circuit for the tri-band notched UWB antenna has been proposed. <![CDATA[Analytical Analysis and Experimental Validation of a Multi-parameter Mach-Zehnder Fiber Optic Interferometric Sensor]]> Abstract Here we report a simple analytical technique to model a Mach-Zehnder fiber optic interferometric sensors that allow us to predict and calculate via computer simulations parameters that are not easily obtained experimentally. This model was calibrated and compared with experimental data using a 120 mm sensor for measurements of temperature, refractive index and water level. For instance, we were able to calculate the effects on the cladding effective index caused by the variation of those physical parameters. Moreover, this analysis could further our understanding of such sensors and allow us to make predictions about their use in different applications and even their behavior with different sensing lengths. <![CDATA[Impact of Pulse Width on the Sensitivity and Range of a Raman-based Distributed Fiberoptic Temperature Sensor]]> Abstract This work presents the operation of a spontaneous Raman scattering-based distributed fiber-optic temperature sensor using a commercial OTDR and a standard EDFA optical amplification in a simple and economic scheme. We present both theoretical and experimental results regarding the sensor's sensitivity and performance in seven different configurations, using OTDR pulses of 100 ns to 4000 ns for two detection regions, in the beginning and ending sections of a 27 km standard single-mode fiber sensor link. The results reveal the trade-off between sensor sensitivity, resolution and range, regarding the use of different OTDR pulsewidths. <![CDATA[Analog Radio-over-Fiber Fronthaul by a WDM-PON employing Double RSOA Self-Seeding and Carrier-Reuse Techniques]]> Abstract WDM-PON has been considered a promising solution for future fronthaul links concerning new mobile networks applications. However, in order to avoid inventory problems and reduce operation costs, there is a need for colorless sources, where the same basic optical source can be used regardless of the desired wavelength. Also, the digital RoF scheme, which has been employed so far, might require a bandwidth that is prohibitive even for optical fiber links. In this paper, we propose and numerically investigate a bidirectional colorless WDM-PON fronthaul transporting analog RoF signals as an alternative to meet these demands. All simulations were performed using a framework calibrated with experimental data. For the downstream, we employ a double-cavity self-seeding technique, while the upstream is performed by a cascaded-RSOAs carrier-reuse approach. BER and EVM simulation analysis are presented for various data rates, modulations formats and RF bands ranging from 1 to 5 GHz, demonstrating the feasibility of our proposed topology as a novel fronthaul approach. <![CDATA[Dual-band System composed by a Photonics-based Radar and a Focal-Point/Cassegrain Parabolic Antenna]]> Abstract This work reports a dual-band radar system composed of aphotonics-based transceiver and a unique dual-band antenna. The proposed antenna consists of an integration of conventional focal-point and Cassegrain parabolic antennas in the same structure, ensured by using a subreflector based on a frequency selective surface. Numerical and experimental results in terms of the antenna reflection coefficient, radiation pattern and gain are reported with excellent agreement over both frequency ranges. The innovative dual-band photonics-based radar transceiver operates simultaneously in the S- and X-bands. The radar system has been properlyvalidated by multiple detections of helicopters and airplanes in real conditions. <![CDATA[Implementation of a Multi-Gbit/s and GFDM-based Optical-Wireless 5G Network]]> Abstract We report the implementation of an optical-wireless 5G network based on generalized frequency division multiplexing (GFDM) and multi-Gbit/s communication. Dual-drive Mach-Zehnder modulator was employed, enabling simultaneously RF signals transport using two 5G candidate bands, namely: 26 GHz band for providing a femtocell with 2 Gbit/s throughput; 700 MHz band for enabling rural access applying a supercell. A vector signal generator provides the broadband 26 GHz signal. The Brazilian GFDM-based 5G transceiver generates the lower-frequency signal, with the advantage of low out-of-band emission. An experimental digital performance analysis illustrates the suitability of the proposed solution to address 5G requirements. <![CDATA[Design, Optimization and Experimental Evaluation of a F-shaped Multiband Metamaterial Antenna]]> Abstract A F-shapedprinted dipole antenna, designed to operate simultaneously at 1.8 GHz, 2.45 GHz and 5.8 GHz is proposed in this work. The main challenge of the project is to find the antenna optimal geometry so that its gain has a higher value in the three operating frequencies in order to be efficiently applied it in the energy harvesting and wireless communication systems. To achieve the proposed operating condition, reduce the antenna return loss and enhance its bandwidth and gain a metamaterial surface was incorporated into its structure. All simulations and optimizations were performed using the Computer Simulation Technology software by employing the Finite Difference Time Domain technique for the electromagnetic equations evaluation. The antenna and metamaterial geometrical dimensions were optimized by using the Genetic Algorithm technique. Numerical and experimental evaluations were performed for the antenna with and without the metamaterial structure incorporated. The results obtained demonstrate the appropriately designed metamaterial ability to improve the antennas performance, increasing their bandwidth and gain and decreasing the return loss value. <![CDATA[Spectral Efficiency Analysis in Massive MIMO using FBMC-OQAM Modulation]]> Abstract This article covers the potential of Filter Bank Multicarrier (FBMC) modulation as an alternative to be used in the future 5G wireless networks in which Massive Multiple-Input Multiple-Output (MIMO) will be deployed. The study compares orthogonal frequency division multiplexing (OFDM) with FBMC. The former is the multiplexing technique in 4G communications and the latter is one of the strongest candidates to replace OFDM in 5G networks. This comparison evaluates the spectral efficiency (SE) of a Massive MIMO (MM) system uplink under a single-cell environment. The diversity in MM permits a self-equalization of the channel, which the FBMC further benefits from, due to the confinement of the subcarrier in an assigned range. Due to the absence of the cyclic prefix, the FBMC has better SE than the OFDM for increasing signal-to-noise-ratio (SNR). One may find a scarce literature covering the FBMC in a large-scale multiuser MIMO scenario, which considers a large number of antennas at the base station (BS). Various scenarios are considered by varying the number of antennas, users and different cell radius. Moreover, the subcarrier modulations are simulated, and not considered Gaussian distributed, as in Shannon limit theory. In some cases, the FBMC allows doubling the cell radius for the same SE value of 3.8 bits/s/Hz/user. For a fixed cell radius of 750m and a SE of 3.5 bits/s/Hz/user, the OFDM requires three times more antennas than FBMC when both modulations are under the same conditions. <![CDATA[Study of the influence of Carbonyl iron particulate size as an electromagnetic radiation absorbing material in 12.4 to 18 GHz (K<sub>u</sub>) Band]]> Abstract This paper presents the influence of different sizes of carbonyl iron particles on the reflectivity measurements of Radar Absorbing Material (RAM). The electromagnetic characterization was performed with a vector network analyzer and a rectangular waveguide in the frequency range of 12.4 to 18GHz (Ku Band). The influence of different parameters such as thicknesses, particle sizes and concentration of carbonyl iron were evaluated. Reflectivity results showed the influence of these parameters on the performance of the RAM. The best reflectivity values (~ −18 dB) were obtained for samples with 60 wt% concentration and 5 mm thickness. We provide information about significantly reflection loss improvement by simply controlling carbonyl iron particulate size. <![CDATA[Material Characterization and Propagation Analysis of mm-Waves Indoor Networks]]> Abstract This paper reports detailed propagation analyses of mm-wave indoor networks based numerical simulations of the wireless coverage and measurements of the propagation coefficient at 28 and 38 GHz. Additionally, material characterization of typical buildings materials used in constructions are presented, including: common brick (with and without electrical installations); plaster walls; glazing, Eucatex panels; wooden doors. The computational simulations have been performed using Altair WinProp™ software in order to predict path loss in LOS (Line-of-Sight) and NLOS (Non-Line-of-Sight) environments. The obtained results contributes to the planning of the fifth Generation of mobile communications networks (5G), operating in mm-waves. <![CDATA[Manufacture of Tapered Fibers and FBG Writing]]> Abstract This article discusses procedures for production of tapered fibers in different diameters (tapers) and Bragg gratings writing (tFBG) in such fibers. The reflection spectra in different tFBGs are compared with a FBG written in standard single-mode fiber (SMF28). The gratings were characterized in terms of their thermal sensitivity. Values reasonably close to 11 pm/°C were expected and were obtained in the different gratings in tapers, confirming that the thermo-optical coefficient is predominant in relation to thermal expansion in gratings written in tapered fibers. <![CDATA[Computational Model and Parameter Extraction of High Speed Semiconductor Optical Amplifier Space Switches]]> Abstract A characterization technique, including a mathematical model involving extensive computational resources, is introduced to study the behavior of an electro-optical space switch based on semiconductor optical amplifier (SOA). The model encompasses the precise emulation of device nonlinearities and its transient performance, allowing the characterization of its transient response. The calibration process includes the evaluation of parasites from the SOA connection, mounting and encapsulation, and parameter extraction of the active cavity. The numerical results are compared to experimental data for various operational conditions, with close similarities. The characterization technique can be adapted for other electro-optical devices, such as directed-modulated lasers, amplitude modulators and electro-optical switches.