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Abstract This paper presents a numerical study and the optimization of very short discrete multi-pump Raman amplifiers using Tellurite-based optical fibers. While most studies about discrete Raman amplifiers usually focus on cases where hundreds of meters of fiber are used, here we consider a multi-pumped Raman amplifier setup with extremely short dimensions, in which the length of the gain media was varied from 2.5 to 30 meters. The optimization process was developed over an broad amplification band from 1520 to 1600 nm, considering a maximum acceptable ripple of 3 dB, and using 2, 3 and 4 pumps with individual powers always below 2.5 W. The results show that it is possible to achieve net gains as high as 10 dB for gain media around 20 meters, and close to 15 dB for 30 meters. These high gains highlight the fact that Tellurite-based optical fibers can be used for the construction of very short and compact broadband amplifiers using just a few pump lasers with modest optical powers.Resumo em Inglês:
Abstract A novel wideband high-selectivity substrate-integratedwaveguide (SIW) filtering antenna with controllable radiation nulls is proposed. This antenna is composed of a two-layered SIW resonator, two radiating slots on the top layer, and two coupling slots on the middle layer. A vertical SMA connector is located at the bottom and feeds two SIW cavities simultaneously. By adjusting the parameters of these slots, three radiation nulls will be achieved, and two radiation nulls can be easily controlled. For demonstration, one prototype of the filtering antenna is fabricated and measured. Measurement results show that the fractional bandwidth for |S11| < -10 dB is 8.9% (3.86-4.23 GHz), the gain is 6.08 dBi at center frequency 4.05 GHz, three radiation nulls are achieved at 3.7 GHz, 4.3 GHz, and 5.19 GHz, respectively. The out-of-band skirt selectivities of two sidebands are 150 and 332 dB/GHz, respectively.Resumo em Inglês:
Abstract This paper will propose an innovative compact, low-cost, low-profile inverted U-shaped patch antenna with a single and dual band-notched ultra-wideband (UWB) with split ring resonators (SRRs). To achieve our main goal based on the reduction of electromagnetic interference in narrowband communications (WLAN, WiMAX, and satellite), four-element rectangular split-ring resonators (SRRs) array are placed nearby the feedline to create notch band at approximately 5.15-5.35 and 5.725-5.85 GHz. The SRRs antenna's measured data indicate a directivity of 8.52 dBi, a gain of 7.18 dBi, a reflection coefficient of -27 dB, and an efficiency of 84.3%. The realized prototype, including the SRRs and CSRRs structures, were carried out using a PCB prototyping machine. Reflection coefficient measurement is obtained using a vector network analyzer (VNA) PNA-X from Agilent Technologies. The measured values of the proposed antenna, with 50 x 38 x 1.6 mm3 in total and constructed on a FR4 substrate with permittivity of ɛr = 4.3, loss tanδ = 0.0024 and substrate thickness of h = 1.6 mm, correlate well with the simulated values. The proposed antenna, compared with other published work, is a good candidate to operate in WLAN, X-band.Resumo em Inglês:
Abstract This paper presents a study on Active Frenquency Selective Surface (AFSS) for applications in modern wireless communication systems. Initially, an FSS with an element inspired by convoluted metallic lines printed on a dielectric substrate of FR-4 is proposed. The unit cell size is equal to 10.2 % of the wavelength in free space for the frequency of 1.53 GHz. An equivalent circuit model is proposed to better understand the operating principle of the FSS. Four Schottky diodes have been inserted in a symmetrical manner for switching, and three operating states are analyzed (all diodes in off state, all diodes directly polarized and therefore conducting, and two diodes conducting and two diodes off). The reconfiguration allows the frequency response to vary between frequencies from 0.8 GHz to 2.5 GHz. The FSS proved to be stable with respect to the angle of incidence of the plane wave on the circuit surface. The simulated numerical results for the designed prototype was obtained by ANSYS HFSS software. The prototype was built and the experimental characterization of the transmission coefficients, bandwidth and resonance frequency was performed. The values obtained in the experiment were compared and discussed with the simulation results, which showed good agreement.Resumo em Inglês:
Abstract This paper attempts to investigate the design of a modified Y-shaped demultiplexer based on photonic crystal. The designed structure is used to select four telecommunication wavelengths. In our design, four resonant cavities (RC)are utilized. A square lattice of silicon (Si) rods immersed in air matrix is used as a fundamental structure. Thus, our study is to investigate the effect of various design parameters on the output frequency. To simulate the performance of the proposed device, the Finite Difference Time Domain (FDTD) approach is used. The obtained results show that the average power transmission, quality factor, channel spacing, crosstalk, and full width at half maximum, are 99.925 %, 4638.785, 19.6 nm, from -40,119 to -24,316 dB, and 0.325nm, respectively. Additionally, the proposed demultiplexer is very compact with a total footprint of 269µm2, which is very suitable to be utilized in compact photonic integrated circuits (PIC).Resumo em Inglês:
Abstract Mobile radio channel and its effects on the radio link path place fundamental limitations on the performance of wireless communication systems. This paper sets out a new approach for wideband modeling of mobile radio channels to classify distinct environments. It applies the hidden Markov model technique to different data sets of the main temporal dispersion parameters of the mobile radio channel: average delay and delay spread. The applied technique has proven to design properly the transitions among those temporal dispersion parameters, mapping statistically the transitions from one point in space to another, and it has revealed to be a feasible option to classify and describe statistically the wideband radio channel in each propagation medium.Resumo em Inglês:
Abstract This paper presents outcomes of a comprehensive investigation of the performance features of the compressed-vdipole antenna, recently introduced in the literature as being particularly suitable for unmanned surface boat applications. The moment-method solution to the rigorously formulated electric field integral equations for the problem, provided an approximation to the distribution of current on the antenna. A comparison of computational results due to this formulation with available measurement data demonstrated very good agreement between the two; to lend credence to the validity of the formulation. Profiles of the antenna’s input and radiation-zone characteristics (including input impedance, return loss, E-field patterns, and maximum directivity) presented in the paper describe how choice of apex angle, antenna electrical length, and degree of compression, influence the performance of the antenna.Resumo em Inglês:
Abstract The development of radio frequency circuits is currently guided mainly through two objectives, which are size reduction and performance improvement of devices. Within a reception or transmission channel, the division and/or combination of power are the most delicate stages due to their large dimensions and high insertion losses, particularly in the case of dividers/combiners based on planar technologies. In this context, this study proposes an analysis and design of a new broadband power divider and combiner using stepped impedance. The power divider/combiner developed is designed to cover a broad frequency spectrum ranging from 1 GHz to 4 GHz, including wireless applications such as Global Mobile Communications Systems (GSM), Industrial, Scientific and Medical (ISM), and Sub-6 GHz 5th Generation (5G) applications. The proposed circuit was analyzed using the stepped transmission line impedance method and designed by Advanced Design System (ADS) on an Epoxy-FR4 substrate with a dielectric constant of 4.4 and a thickness of 1.58 mm. The achieved results showed excellent characteristics in terms of transmission across the input and output terminals, mismatches at all three terminals, and isolation among output terminals. A prototype was built and the measured results showed good agreement with those obtained by simulation.Resumo em Inglês:
Article This paper develops an easy design analysis for a simple high selective T-shaped band-stop filter (BSF) loaded with a capacitance. It applies the developed design theory to obtain an appropriate capacitance value for tuning the cut-off frequency. This paper clearly explains the design mechanism for such a simple tunable BSF using ABCD matrices. Simulated filters loaded with capacitances (up to 1.1 pF) show a change in rejection frequencies from 2 GHz (un-tuned) down to 1.047 GHz with 50dB rejection and around 36% -3dB fractional bandwidth. It also shows the effect on pass frequencies which change from 1 GHz down to 111 MHz, while the separation between pass and stop frequency remains around 1 GHz. Measurements on fabricated prototypes match the simulation and theory for tunable frequencies closely. It also compares the performance of the filter with previously reported similar structures.Resumo em Inglês:
Abstract In this paper, the application of AI and machine learning (ML) to the study of wireless propagation channels is investigated in two parts: first, an artificial neural network model is used to improve path loss prediction, and then, a pattern recognition model using multilayer perceptron (MLP) networks is used to identify and remove impulsive noise in power delay profiles (PDP). These studies were conducted based on field measurements in the 2400 MHz band in a public square with vegetation. The results are analyzed and compared with ordinary least squares (OLS) nonlinear regression results and results from similar studies. The Root Mean Square Error (RMSE) values between the experimental results of mean path loss and those provided by each propagation model are presented. The adjustment performed by OLS nonlinear regression and ANN significantly reduced the RMSE. The best results are those presented by artificial neural networks, with RMSE of 0.39 when using four neurons in the hidden layer of the ANN. The ANN used to identify and remove impulsive noise in power delay profiles (PDP) through pattern recognition proved to be more efficient than the CFAR technique. ANN technique found a larger number of valid multipaths compared to the CFAR technique.Resumo em Inglês:
Abstract In this article, a comprehensive analysis of the approach known as Split-Step Wavelet Parabolic Equation (SSW-PE) in modeling radio wave propagation is presented. The SSW-PE introduces innovations, such as the application of narrow-angle and wideangle approaches, referred to as NAPE and WAPE, respectively. Furthermore, the SSW-PE demonstrates the incorporation of refractivity variations, modifications in terrain modeling for better representation, and considerations of surface boundary conditions. In addition to its innovative aspects, this study aims to provide a complete guide for effectively replicating the algorithm, thereby promoting the advancement of propagation studies using wavelets. The effectiveness and applicability of this approach are validated through comparative studies with well-established solutions, including the Discrete Mixed Fourier Transform (DMFT) version of the Split-Step Parabolic Equation (SSPE) method. Comparisons with measurements from real propagation cases are also conducted. Statistical analysis confirms the innovative potential of the SSW-PE algorithm, which also offers computational efficiency for rapid and consistent simulations. Thus, this article contributes to a comprehensive and innovative analysis, providing tangible resources for the research community interested in expanding this methodology.