Scielo RSS <![CDATA[Journal of Microwaves, Optoelectronics and Electromagnetic Applications]]> vol. 16 num. 3 lang. es <![CDATA[SciELO Logo]]> <![CDATA[Quantum Particle Swarm Optimization for Synthesis of Non-uniformly Spaced Linear Arrays with Broadband Frequency Invariant Pattern]]> Abstract This paper describes a method using Quantum Particle Swarm Optimization to obtain a broadband frequency invariant pattern for synthesis of nonuniformly spaced linear array of isotropic antennas. Two cases related to this work using QPSO have been studied, namely, in the first case, the generated frequency invariant far-field pattern is broadside in the vertical plane and in the second case, the far-field frequency invariant pattern is scanned in a particular direction. An effort is made such that the side lobe level and first null beam widths of the patterns are made similar to their related desired values. The two cases are presented in this paper to show the effectiveness of the proposed method in achieving the desired specifications. Even though, the developed method is utilized here for a linear array of isotropic antennas; it can be extended to other type of arrays. The performance of this algorithm is validated by duly comparing it with firefly algorithm. <![CDATA[A Low Complexity Iterative SLM-OFDM for SHF band applications]]> Abstract The transmitted Orthogonal Frequency Division Multiplexing signal in systems such as Wireless LAN, Mobile WiMAX, Digital Video Broadcasting (DVB) operating in the Super High Frequency (SHF) band suffers from high Peak to Average Power Ratio. This is reduced in Selective Level Mapping (SLM)approach but at the expense of increased complexity. In this paper, we propose iterative selective level mapping based on an orthogonal phase sequence set for PAPR reduction with reduced computation complexity. The Golay Complementary pair is used as basis to generate the phase sequence set. Analysis of the aperiodic properties of individual phase sequence and the entire phase sequence set is carried out. It is suggested that mean-square value of auto correlation be an additional measure to choose phase sequence set. Simulations are carried out to assess the PAPR and complexity reduction achieved. The proposed phase sequence set achieves a 1.2 dB and 2.4 dB PAPR improvement over conventional SLM and OFDM respectively for maximum of 16 candidate signals at iterative threshold of 6 dB. The computational complexity reduction achieved is 59%. <![CDATA[A System Based on Artificial Neural Networks for Automatic Classification of Hydro-generator Stator Windings Partial Discharges]]> Abstract Partial discharge (PD) monitoring is widely used in rotating machines to evaluate the condition of stator winding insulation, but its practice on a large scale requires the development of intelligent systems that automatically process these measurement data. In this paper, it is proposed a methodology of automatic PD classification in hydro-generator stator windings using neural networks. The database is formed from online PD measurements in hydro-generators in a real setting. Noise filtering techniques are applied to these data. Then, based on the concept of image projection, novel features are extracted from the filtered samples. These features are used as inputs for training several neural networks. The best performance network, obtained using statistical procedures, presents a recognition rate of 98%. <![CDATA[Dual U-Slot Loaded Patch Antenna with a Modified L-Probe Feeding]]> Abstract In this paper, a modified L-strip fed patch antenna is theoretically analyzed for wideband applications. Dual U-shaped slots are incorporated in the radiating patch and a maximum bandwidth of 16.93% (2.65 GHz to 3.14 GHz) is achieved. Further, when two parasitic elements are used, antenna bandwidth improves up to 25.89% (2.90 GHz to 3.77 GHz). The maximum gain of dual U-slotted patch and with parasitic elements is 8.23 dBi and 8.46 dBi respectively. Antenna parameters are calculated by CST Microwave studio and equivalent circuit model theory is presented. The proposed antenna is fabricated and the measured results compare well with the theoretical as well as simulated results. <![CDATA[A Numerical Mode-Matching Method Based on Multiple-Knot Cubic B-Splines Applied to the Analysis of Well-Logging Tools]]> Abstract The numerical mode-matching (NMM) technique is a very efficient approach to analyze well-logging tools used for hydrocarbon exploration. This problem is typically modeled as a cylindrically layered medium (subterranean formation) including both horizontal and vertical stratifications. In this paper, we present a new NMM formulation based on the use of B-splines expansion functions with variable knot multiplicity to represent the dependency of fields on the vertical direction, and cylindrical Bessel functions to represent the fields along the radial (horizontal) direction. We show that this type of expansion allows to better capture the spatial variation of the electromagnetic field near vertical layer interfaces. Illustrative examples elucidate the advantage of knot multiplicity in the modeling of earth formations with anisotropic and lossy layers. A case study on compensated dual resistivity (CDR) well-logging tool sensors is also presented based on the proposed method. <![CDATA[A Compact Wideband Patch Antenna Loaded by Interdigital Capacitor with Equivalent Circuit Model]]> Abstract In this paper a wideband microstrip patch antenna (MPA) using aperture coupling feeding technique with bandwidth (BW) of 28% is designed at first. Afterwards for the pupose of reducing the size of the radiating element, the composite right/left hand (CRLH) concept is used by implementing an interdigital capacitor (IDC) as series left hand component in the antenna. The slot in the ground plane acts as a left hand parallel inductor. Through this technique, three operation modes of CRLH antenna is excited and by appropriate adjusting of the IDC parameters, closing and mixing of resonant frequencies are achieved. Size reduction in the order of 15.5% and 6.2% in the patch and slot dimensions compared to the initial designed antenna is obtained respectively. The equivalent circuit model of the final designed antenna is presented and simulated. The final designed antenna is fabricated and tested. <![CDATA[Design of coaxial aircell fixture for the measurement of electromagnetic properties]]> Abstract Coaxial aircells are designed and fabricated to measure the electromagnetic properties of ferrite materials in the frequency range from 1 MHz to 3.6 GHz. These S-parameters are actually measured connecting the aircell to a vector network analyzer (VNA). The electromagnetic properties such as complex permittivity and complex permeability are extracted using Nicolson-Ross-Weir (NRW) method and also suitable air-gap corrections are made. To optimize the measured result and to estimate the error, the aircells are characterized in terms of their phase constant and resistivity of the aircell conductor. The measurements clearly showed that the electrical length is longer than the mechanical length of the aircell at all frequencies. The arithmetic mean of the resistivity of aircell which is of 7mm line size and 60mm length is about 66 nΩm. This paper presents a simple method by which the phase constant and resistivity of the aircell can be determined accurately. This is done with the transmission measurements made using a VNA. <![CDATA[Heuristics for the optimized deployment of small cells in next-generation networks]]> Abstract Heterogeneous Networks (HetNets) have been introduced as an alternative means of improving the overall network capacity. However, HetNets increase the complexity and cost of transport due to the large number of smallcells (SCs) that have to be connected, and hence, it is essential to investigate the best way to plan the joint deployment of radio and transport resources. For this reason, some planning strategies have been put forward in the literature with the aim of reducing both the number of SCs and amount of transport. These systems are generally based on OFDM (Orthogonal Frequency Division Multiplexing) which uses a radio frequency range from 2 to 20 GHz. However, those papers do not evaluate path loss, which is a major component in the analysis or how to design the link budget of a telecommunication system. In this paper, we examine a heuristic for the joint planning of radio (i.e., SCs) and transport resources (i.e., point-to-point fiber links) by using suitable propagation models for next generation networks. Through the proposed heuristics, it is possible to save up to 12% of the total costs of the network deployment incurred by other systems found in the literature. <![CDATA[A Hybrid Path Loss Prediction Model based on Artificial Neural Networks using Empirical Models for LTE And LTE-A at 800 MHz and 2600 MHz]]> Abstract This article presents the analysis of a hybrid, error correction-based, neural network model to predict the path loss for suburban areas at 800 MHz and 2600 MHz, obtained by combining empirical propagation models, ECC-33, Ericsson 9999, Okumura Hata, and 3GPP's TR 36.942, with a feedforward Artificial Neural Network (ANN). The performance of the hybrid model was compared against regular versions of the empirical models and a simple neural network fed with input parameters commonly used in related works. Results were compared with data obtained by measurements performed in the vicinity of the Federal University of Rio Grande do Norte (UFRN), in the city of Natal, Brazil. In the end, the hybrid neural network obtained the lowest RMSE indexes, besides almost equalizing the distribution of simulated and experimental data, indicating greater similarity with measurements. <![CDATA[ANALYTICAL COMPARISON OF THE PERFORMANCE OF ADAPTIVE MODULATION AND CODING IN WIRELESS NETWORK UNDER RAYLEIGH FADING]]> Abstract In this paper, an analytic comparison between adaptive modulation (AdM) and adaptive Forward Error Correction (AdFEC) in wireless network telecommunication systems is performed. Through the Gilbert-Elliott model's, the Packet Error Rate (PER) is calculated and both the throughput and the delay, for different modulations and error correction capacity, have been also computed. For the throughput criterion, the results show that the AdFEC outperforms AdM for higher values of Signal Noise-to-Ratio (SNR). However, when the SNR has low value the adaptive modulation performs better. In case of delay criterion, the mean time to transmit a packet using AdM is lower than when AdFEC is used. <![CDATA[SmartCoM: Smart Consumption Management Architecture for Providing a User-Friendly Smart Home based on Metering and Computational Intelligence]]> Abstract With advances in information technology for health and wellness, Smart Home-based solution providers using Internet of Things (IoT) technologies, have increased in importance and become accepted as an alternative means of saving energy when based on Home Energy Management Systems (HEMS). This paper defines a modern architecture (SmartCoM), which is implemented to monitor and manage residential dwellings by using IoT technologies. This involves setting out the parameters that can make interoperability possible between measurement and management, and the layers of data communication, which are the features necessary for the hardware required for monitoring and measurement. In addition, an interface is defined by a middleware layer to integrate the management of external installations and the visualization of data by means of a cloud service. The SmartCoM end-to-end architecture is defined in detail from the standpoint of the consumer and optimization strategies are employed for both the end customer and the utility. The main advantages of using SmartCoM were confirmed by the numerical results obtained from the proposed architecture. This paper ends by showing the current position of SmartCoM as well as suggesting further stages for this line of research. <![CDATA[High-Resolution Imaging Utilizing Space-Frequency DORT Combining the Extrapolated Virtual Array]]> Abstract Space-frequency DORT (SF-DORT) is an effective time-reversal (TR) imaging method due to its immunity to the noise and adaptability of complex environment. However, some potential drawbacks, such as low range and co-range resolutions, make SF-DORT inferior to the Space-frequency MUSIC (SF-MUSIC). In this paper, we propose a novel high-resolution imaging method utilizing SF-DORT combining an extrapolated virtual array (EASF-DORT). The virtual extrapolated TR array is created by autoregressive vector extrapolation (ARVE). In this way, the aperture of the TR array is extended significantly and the drawbacks associated with SF-DORT can be improved. Simulation results demonstrate that SF-DORT combining the extrapolated virtual array achieve much higher range and co-range resolutions than conventional SF-DORT. <![CDATA[Designing Four Notched Bands Microstrip Antenna for UWB Applications, Assessed by Analytic Hierarchy Process Method]]> Abstract In this study, a novel microstrip fed Ultra Wideband (UWB) antenna is presented. The proposed antenna, with a size of 26×30×1.6mm3, is capable of removing four bands of interference in the coverage band. Firs, three filtered bands are created by cutting U, L, and C-shapes, a horizontal line on the patch, and fed line of antenna. The fourth notch is created by a new method that involves the use of a metalized via-hole and a C-shaped strip line in the rear side of the radiation patch. In the next step, the proposed antenna is compared with similar models with regard to different features such as size, bandwidth, and the number of the filtered frequency bands, in a new framework based on the Analytic Hierarchy Process. Thus, with a comprehensive comparison, the functional aspects of the proposed antenna are presented. The characteristics of the proposed antenna, such as radiation pattern, gain, and return loss (S11&lt;-10dB), were measured; the correspondence between the simulated and measured results was acceptable. <![CDATA[A Balanced-to-Single-Ended Wilkinson Power Divider]]> Abstract A balanced-to-single-ended (BTSE) Wilkinson power divider of planar microstrip structure is proposed in this paper. It has a balanced input and two single-ended outputs. Cascade of a balun and a conventional power divider can be replaced by this proposed structure. Based on the theory of mixed-mode S parameters and the admittance matrix method, the critical parameters are determined. The four-port network is analyzed by simplifying it to two-port network with other ports matched at the central frequency. Then the key parameters are derived and the impact of a freely selected variable on the bandwidth is also discussed. An example of 2.4GHz BTSE power divider is designed. The simulated and measured results show the effectiveness of the method: differential-mode transmissions are better than −3.25dB, common-mode transmissions are lower than −28.6dB, common-mode return loss is −0.10dB, differential-mode return loss and isolation is lower than −23.7dB. While the operating bandwidth is 20%. <![CDATA[New methodology for modeling, design and implementation of RF power amplifiers]]> Abstract This work presents a new methodology for modeling, design and implementation of power amplifiers in different technologies. As result of comparison, a flowchart with a new methodology is proposed which can be useful for the designer to design and implement power amplifiers with low, medium and high power devices in different technologies. This paper is divided in 4 parts: The first one is an introduction to the importance of modeling and design techniques in the final implementation of power amplifiers for the modern communication systems. The second one details the modeling process for different technologies, which final result is a unified model. The third part is related with the characterization of high power transistors, with special emphasis on substrate characterization and final implementation of a power amplifier. Finally, in the fourth part, the new methodology is proposed based on the comparisons of previous procedures. <![CDATA[Dynamic Digital Holography for recording and reconstruction of 3D images using optoelectronic devices]]> Abstract In this work, we present the optical recording and reconstruction of dynamic 3D digital holograms using optoelectronic devices. Digital Holography technique allows recording and reconstruction of three-dimensional images of real objects, since a hologram presents both the intensity and phase information about the object. The experimental implementation of digital holographic systems for recording, as well as for numerical and optical reconstruction of three-dimensional objects became possible. We developed an experimental setup that allowed the optical recording (construction) of dynamic digital holograms (DHs) from real three-dimensional objects in CCD cameras, together with their numerical reconstruction and their optical reconstruction in a dynamic process by using a spatial light modulator, SLM; it was used a single holographic experimental setup in the entire process. We have obtained good results that enable excellent prospects for applications in recording and reconstruction of 3D scenes. <![CDATA[Time Reversal Imaging Based on the Space-Frequency ESPRIT]]> Abstract A novel time reversal approach for the point target imaging is proposed in this paper. This method requires only single measurement by the time reversal array, and it exploits the space-frequency decomposition plus the rotation invariance of the signal subspace for the target detecting. Numerical simulations are carried out to validate the imaging performance of the method for single target located at different positions in homogenous and continuous random medium respectively. The results indicate that the proposed method performs better than the conventional signal subspace based space-frequency algorithm both in imaging resolution and efficiency. <![CDATA[A simple strategy to design broadband low power consumption distributed Raman amplifier]]> Abstract In this work, a simple strategy to design wideband low power consumption Raman amplifiers is demonstrated for a three-pump configuration using a low water peak optical fiber. The approach is based on the introduction of a novel numerical measure, which quantifies and isolates pump-pump interaction contribution to gain profile and analyzes its correlation to amplifier minimum ripple. The method tailors the amplifier gain spectrum over 80nm bandwidth with a ripple smaller than 1dB, a gain on the order of 4dB for up to 75km fiber length, and a total pump power consumption smaller than 300mW. <![CDATA[Measurements of Medium Wave HD Radio Reception in a Dense Urban Region]]> Abstract This paper presents the results of measurements of medium wave received field strength, HD Radio audio quality and maximum coverage distances in a dense urban region. Analog AM and digital HD Radio signals broadcasting the same content were simultaneously transmitted in São Paulo, the largest city in Brazil. The received signal intensity and the reception quality were recorded along radial routes of up to 45 km from the transmitter under both mobile and static conditions, enabling the comparative assessment of the digital and analog system performances. <![CDATA[Design of Ground Penetrating Radar Antenna for Detecting Soil Contamination at L-band Frequencies]]> Abstract Maintenance of oil pipelines is an issue of great concern for oil companies. Soil contamination is caused by oil leaks from underground pipelines. Ground penetrating radar (GPR) is a rapid and relatively inexpensive technique used for locating and characterizing soil contaminated sites without producing fractures and causing further migration of contaminants. One of the most critical hardware components for the performance of GPR is the antenna system. The present paper reports on the design and simulation of a pyramidal horn antenna operating at L-band frequencies (1- 2 GHz) to detect soil contamination. A prototype model of the GPR system setup is developed to simulate the electromagnetic fields in different soil types. The dielectric permittivity of soil, needed in order to carry out simulations during the design process, is measured and analytically represented by Debye relaxation model. The contrast in the dielectric permittivity between contaminated and uncontaminated soils is the most important parameter to be considered for detecting the presence of contamination. The application of GPR is proved to be well-versed in the investigation of soil contamination. <![CDATA[Design of Biodegradable Quadruple-shaped DRA for WLAN/Wi-Max applications]]> Abstract A novel Quadruple-shaped Dielectric Resonator Antenna (DRA) excited by a coaxial feed is investigated. The dielectric used for investigation is biodegradable polymer based dielectric material having a dielectric constant (εr) of 3.45 and dielectric loss tangent (δ) =0.02. The resulting antenna offers broad impedance bandwidth of 63.2% for |S11| &lt; −10 dB from 2.8 to 5.2 GHz frequency band. This antenna is suitable for practical use in WLAN (5.15-5.35 GHz) and Wi-Max (3.4-3.69 GHz) applications. The results show the peak gain of the antenna is 4.5dBi at resonant frequency 3.8 GHz. It is also observed that the new proposed structure of Quadrupleshaped DRA offers broadside radiation patterns and high efficiency for the entire operating band. The simulated and experimental results are well in agreement.