Scielo RSS <![CDATA[Journal of Microwaves, Optoelectronics and Electromagnetic Applications]]> vol. 15 num. 4 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[Modeling an Optical Network Operating with Hybrid-Switching Paradigms]]> Abstract The continuous increasing of the Internet traffic has brought serious concerns about capacity exhaustion of the optical infrastructure in a medium term horizon. Taking into account the optical networks, comprising the Internet backbone, the strategies to avoid this catastrophic scenario point to the development of new technologies that enable the capacity expansion, as well as to a better utilization of network resources (spectrum or wavelengths). The elastic optical network, considered as a realistic perspective for the infrastructure, optimizes the required spectrum and improve the efficiency of resources utilization. However, it is based on optical circuit switching paradigm that tends to waste resources due to idle times of reservation process. Since in some dedicated optical networks, like data center networks, certain optical switching paradigms have become reality, it is expected that in the coming years not only an elastic optical network, but also a hybrid network, in terms of switching paradigms, be brought to reality. Considering this scenario, the present paper addresses some issues on the modeling of an optical network working with hybrid-switching paradigms. <![CDATA[The study of the ground plane effect on a Multiband PIFA Antenna by using Genetic Algorithm and Particle Swarm Optimization]]> Abstract The ground plane plays an important role on the performance of a planar inverted-F antenna (PIFA). In this regard, the ground plane modification using slots is proposed in this research to obtain a dual band antenna for WiMAX application. Popular optimization techniques, as genetic algorithm (GA) and particle swarm optimization (PSO), were used to design the shape of the ground plane in order to improve the bandwidth and to achieve dual band antenna instead of single band antenna. The proposed method divides the overall ground plane into different cells. Through this technique it is possible to obtain a dual band antenna reduced by more than 50%, thereby reducing the overall ground plane. Both GA and PSO designs are provided. This new method shows many advantages over PIFA antenna in terms of performance and weight. <![CDATA[Compact Microstrip Low-pass Filter with Wide Stop-band Using P-Shaped Resonator]]> Abstract This paper, a compact low-pass filter (LPF) with an Elliptic function response using P-shaped resonators is presented. The LPF with simple structure results in the low insertion loss less than 0.1 dB and high return loss better than 20 dB, in the pass-band. The proposed filter with a −3 dB cutoff frequency of 2.61 GHz is fabricated and measured. The measured results show that the proposed LPF has significant advantages such as a wide stop-band from 2.9 GHz to 17.3 GHz with the suppression level better than −20 dB, and it has an acceptable sharp frequency response in the transition band. The measurement results are in good agreement with the simulation results. <![CDATA[Boolean Operators to Improve Multi-Objective Evolutionary Algorithms for Designing Optical Networks]]> Abstract The physical topology design (PTD) of optical networks is frequently accomplished by combining several solutions in an iterative way, especially if meta-heuristics are deployed for this purpose. Suitable operators to recombine information of network topologies aiming at creating innovative options for designing networks are very useful. Operators that preserve desired properties can improve the quality of the meta-heuristics utilized for solving the PTD problem. In this paper, we propose new crossover operators by using the OR and XOR operations to improve multi-objective evolutionary algorithms applied to design optical networks. We performed comparisons between the proposed crossover operators and the traditional uniform crossover. The proposed operators showed to be a suitable alternative to design optical networks. We obtained better solutions or at least solutions with the same quality when compared to solutions achieved by traditional approaches, but the execution time required by our proposal is smaller. <![CDATA[Thermal Monitoring of Photovoltaic module using Optical Fiber Sensors]]> Abstract This paper proposes the use of fiber Bragg gratings (FBG) in thermal monitoring of photovoltaic (PV) modules. Results acquired from FBG sensors were compared with two commonly used temperature sensing techniques in PV modules: PT100 sensors and infrared cameras. The experiments were performed using a PV module in actual operating conditions (varying ambient temperature and wind speed). Temperature changes in PV module were monitored with 27 FBG sensors installed on its front surface. During the experiments the ambient temperature, intensity of solar radiation and wind velocity were also monitored. The acquired results showed that FBG sensing technology has a potential for the proposed application. <![CDATA[Link Optimization and Performance Analysis of a 40 Gbps DQPSK Modulated Ultra DWDM System with 32 Orthogonally Polarized channels]]> Abstract The demand for higher speed at a lesser transmission cost per bit resulted in growth of optical networks with improved spectral efficiency even at narrower channel spacing. Incorporation of multilevel modulation formats in DWDM system led to the exploration of the 25 GHz channel grid, popularly known as Ultra Dense Wavelength Division Multiplexed (UDWDM) systems, opening new research frontiers. At such channel spacing's, non-linear optical effects impose severe system impairments and hence robust modulation schemes are currently being investigated. This paper presents a simulative model to implement and analyze alternative polarized DQPSK modulated UDWDM system to evaluate its resilience to XPM and fiber nonlinearity. An UDWDM system supporting 32 channels, each operating at 40 Gbps and spaced at 25 GHz is studied numerically for long-haul optical communication system using OptiSystem simulator to estimate OSNR penalties to mitigate XPM effects. The major detrimental factors encountered in link design have been estimated to evaluate the system performance in terms of Q value for different number of channels and with varied input power. The analysis reports acceptable performance for DQPSK format up to a link distance of 1500 Km and also claims a better tolerance to dispersion and nonlinearities at higher input power levels. <![CDATA[Design and Modal Analysis of Photonic Crystal Fiber for Dispersion Compensation over Broadband Range]]> Abstract In this paper we have presented the four new investigations using different structures of Photonic Crystal Fiber (PCF) for broadband communication applications and narrows down on the design which can provide largest flat negative dispersion. The new structure model is optimized based on the combination of modal properties and dispersion compensation. The results were recorded over a transmission frequency range from 190.95 THz to 245.73 THz i.e. 1.22 µm to 1.57 µm with a dispersion −704.62 ps/nm/km. The results obtained from the new different PCF structures are compared with reported results for different 2D PCF models so far. <![CDATA[Experimental Study of Transmission and Reflection Characteristics of a Gradient Array of Metamaterial Split-Ring Resonators]]> Abstract A study of a non-uniform metamaterial array consisting of six split-ring resonators of varying diameters is conducted experimentally to measure the transmission and reflection characteristics that arise from asymmetry in the longitudinal direction. Such characteristics are examined and compared with their counterpart symmetric scattering coefficients associated with a uniform split-ring array. In the non-uniform array the ring diameters vary in steps of 0.5 mm, which yields a gradient geometry. Inserting the non-uniform array in an X-band waveguide operating below cutoff provides a transmission band wider than that obtained from the uniform array. Different from the uniform array, for which the magnetic resonance frequency is on the left and away from the electric resonance frequency, in the gradient array the magnetic response lies inside the electric band. <![CDATA[A New Simplified Approach for Design of Dual-Band Wilkinson Power Divider with Two and Three Transmission Line Sections Using Only Even-Mode Analysis]]> Abstract In this paper, design of dual-band equal-split Wilkinson power divider (WPD) with two and three transmission line (TL) sections is tackled from the perspective of a new simplified mathematical approach as compared to the previously presented work. It is mathematically proven and experimentally verified that only even-mode circuit analysis suffices for outlining the design guidelines for such WPDs which greatly reduces the mathematical complexity. Owing to the cascaded nature of the TL sections and using even-mode analysis, firstly, design equations and design graph are drawn for the two TL sections WPD. The technique is then extended to the design of a three TL sections WPD with simplifications in the circuit, rendering the approach much simpler and mathematically less rigorous (as compared to the previous work). The comparisons of the proposed and previous design approach are drawn. To prove the efficacy of the presented simplified design approach, a two TL sections and a three TL sections WPD are designed at 1GHz and 2.4GHz and fabricated. The measured S-parameters show good conformance with the simulated results indicating practical viability of the presented simplified approach. For instance the insertion loss in the two and three TL section is better than 3.2dB. The return loss and isolation between the ports in two TL sections WPD come out to be better than 28dB and 29dB, and in three TL sections is better than 30dB and 29dB respectively at the two design frequencies. <![CDATA[A Performance Evaluation of WLAN-Femtocell-LTE beyond the Capacity Crunch. Does Femtocell have to overcome WLAN or can they coexist in HetNets?]]> Abstract This paper originates from a practical experiment based on Mesh Networks. The promising results obtained from this experiment prompted us to discuss in greater depth whether Wireless Local Area Networks (WLAN) are still useful for current communications. This means that on the one hand femtocells can be defined as small base stations that use the same frequency bands as cellular networks. This has become a key feature in LTE to improve capacity and enhance data rates. On the other hand, WLAN, which in terms of infrastructure is similar to femtocells due to the IP backhaul network, seems to have outgrown its usefulness largely because it is being replaced by femtocell technology. In this paper, an attempt is made to clarify this uncertainty through an extensive analysis beyond the capacity crunch of both technologies. The work was undertaken by first working separately and in a second stage, working together to provide possible hybrid access to help offload traffic. Using cellular systems to underpin our research, we give examples of the capacity crunch for femtocells and WLAN through an extensive simulation campaign. <![CDATA[Use of an Artificial Neural Network-based Metamodel to Reduce the Computational Cost in a Ray-tracing Prediction Model]]> Abstract The purpose of this article is based on analyzing the use of RTQ3D (“quasi-3D” ray tracing technique) to produce the value of the initial electromagnetic fields or fitness for a hundred and sixty receivers according to the possible positions of two antennas to be distributed in a closed environment. The problem variables consist of the values of the magnetic fields for one hundred and sixty receptors depending on the positions of the antennas to the base stations, which serve as input data for the algorithm to the RMLP (Artificial Neural Network, multilayer perceptron with Real backpropagation learning algorithm). The values of the magnetic fields associated with the positions of the antennas are the values to be learned by the network, the teacher of RMLP. This study aims to develop efficient techniques for optimization of electromagnetic problems. We use the PSO (Particle Swarm Optimization) algorithm associated with a metamodel based on an ANN (Artificial Neural Network). Specifically, we use the MLP (Multilayer Perceptron) with the backpropagation algorithm in order to evaluate objective functions in an efficient way. The ANN will be used to assist the technique of “quasi 3D” ray-tracing in order to reduce the high computational cost of this technique in PSO optimization. <![CDATA[Improvement of Circularly Polarized Slot-Patch Antenna Parameters by Using Electromagnetic Band Gap Structures]]> Abstract This paper is devoted to the design of a novel Electromagnetic Band Gap (EBG) circularly polarized slot-patch antenna in multilayered configuration. The operating frequency band can be controlled via the disk radius and adjusting the slit lengths. An arrangement combining the circular slot-patch antenna design and feeding sources included are considered is necessary. Due to the exisiting of two feeding points, Position of both feeding points will permit Right-hand and Left-hand circular polarization operations. Thickness of substrate is chosen to reduce the spurious surface wave and width. The same technique will be used for the EBG cirlcularly polarized circular slot-patch antenna network and carry two benefits (such as improvement of bandwidth, beamforming, creating zero radiation beams) and filtering characteristics of the resonator (spatial filtering, increased directivity, misalignment) due to the resonant structure itself. The analysis provided will confirm successfully the various proposed structures and interest occupied by these types of antenna. Two approaches, one introduced by one layered Circularly-Polarized Patch-Slot antenna design with some changes in material configuration and the other produced by multilayered structures with different dielectric constants in the EBG resonator, are simultaneously used as key controllers of directivity enhancement. <![CDATA[Performance evaluation of digital TV and LTE systems operating in the 700 MHz band under the effect of mutual interference]]> Abstract This paper presents results of the assessment of the interference between digital TV systems and LTE systems operating in adjacent bands in the 700 MHz frequency range. Measurement results are presented and used to validate a simulation tool that allows different scenarios of interference between the SBTVD systems and LTE to be created. The simulation tool was then used to analyze the probability of interference dependence on the distance between systems, transmission power, number of interferers and other parameters to allow the definition of conditions for the harmonious coexistence of the systems. <![CDATA[Ultra Wide Band Radar Cross Section Reduction of a Perfectly Electric Conductor Sphere by the Application of Multilayer Metamaterial Coatings]]> Abstract A full-wave analytical method using the addition theorems and Hertzian potential functions are used to compute the radar cross section of a sphere coated by several layers composed of common materials and metamaterials. The minimization and maximization of radar cross section of a perfectly electric conductor sphere with such coatings are realized in a frequency band-width and in a wide interval of angles. One of the novelities of this contribution is, taking into dispersion relations of physically realizable metamaterials. So that the optimization procedure for RCS reduction is applied due to the coefficients describing dispersion characteristics. The method of least square is used for the design of a class of radar absorbing materials. The minimization of the error functions are performed by the combination of genetic algorithm and conjugate gradient method. It is shown that the proposed method of computation of radar cross section and its extremization effectively leads to the design of dispersive and isotropic metamaterials for the realization of radar absorbing materials. <![CDATA[Simulating a Multi-Vehicle Traffic Sensing System Based on Radio Tomographic Imaging]]> Abstract One of the most recently developed wireless technologies is Radio Tomographic Imaging (RTI). RTI employs a wireless sensor network that produces images of the change in the electromagnetic field of a monitored area using Received Signal Strength (RSS) measurements. This allows the tracking of device-free objects such as humans and cars. This paper is the first to propose and validate a simulation model that simulates RSS measurements for arbitrary RTI networks, based on the ZigBee communication protocol. The simulation model allows the specification of an RTI network from the ground up, including node positions, network size and geometry and RSS measurement processing. Furthermore, this paper demonstrates the implementation of the simulation model to an enhancement of a recently proposed RTI system, which acts as a roadside surveillance system. The enhancement includes three newly proposed techniques, namely a new weight matrix calculation method, a new node spacing setup and a new vehicle detection method. The simulation results indicate that it is possible to detect both one or two family sized cars simultaneously. Using techniques that reduce RSS variance due to multipath effects and the newly proposed methods, simulated vehicle detection performance is demonstrated to be between 95% and 100%.