Abstract in English:

Abstract Cavity perturbation method is applied in this paper to assess the electric permittivity (ɛr) and loss tangent (tanδ) of dielectric materials at the 3.5 GHz microwave frequency of the 5G test band of the Global System for Mobile communications Association (GSMA) spectrum. These characteristics are important in the design of radomes, antenna fixture parts and spacers for airfilled multilayer structures for antennas and microwave circuits. A cylindrical cavity with two ports was designed and fabricated to operate in the TM010 mode. The characterization process includes the preparation of cylindrical samples with thickness of 12.5 mm with concentrations of 25%, 50%, 75% and 100% of the following materials: acrylonitrile butadiene styrene (ABS), Tritan, polyethylene ethylene glycol terephthalate (PETG), acrylonitrile styrene acrylate (ASA), polyamide (Nylon), Polylactic acid (PLA) and CRcarbon. The measured S-parameters allowed calculating the quality factor, the electrical permittivity and the loss tangent of the analyzed samples by comparison to numerical results obtained by the Finite Element Method (FEM) using Ansys HFSS. The results obtained demonstrate that the filling percentage of the samples is an efficient technique to control the effective dielectric constant of 3D printed parts, provided that the filling mesh dimensions are much smaller than the operating wavelength. Such a condition is easily achieved at 3.5 GHz with modern 3D printers. Finally, a dielectric resonator antenna has been designed and measured, whereby excellent agreement between the simulation predictions and measured results has been achieved, hence demonstrating the accuracy of the proposed dielectric measurement technique.

Abstract in English:

Abstract This work presents a closed-form formulation for analyzing perturbed resonant cavities with metallic walls, implemented using Substrate Integrated Waveguide (SIW) technology. In particular, it focuses on planar SIW filters in which the perturbations consist of grounded metallic vias. Codified in MATLAB, the proposed formulation provides a powerful tool for the design of microwave filters based on these structures. The proposed approach computes the internal electric and magnetic field distributions, scattering parameters, and derived properties such as group delay. Moreover, the code solves the circuits up to 100 times faster than full-wave simulators while using approximately 50% less RAM. The model is validated through comparisons with full-wave simulators as well as by the design, fabrication, and testing of a C-band SIW filter.

Abstract in English:

Abstract This paper introduces a new approach to reconfiguring an antenna’s operating frequencies by switching between an inverted-F antenna (IFA) mode and a loop mode. This frequency agility is achieved by incorporating a switch at the end of the antenna trace, which connects or disconnects the trace from the antenna ground, thereby altering the antenna's resonant behavior depending on the selected mode. To validate the concept, a prototype antenna was fabricated, and the measured results showed strong alignment with simulation predictions. In the IFA mode, the antenna exhibits two resonant frequencies around 1 GHz and 2 GHz, while in the loop mode, it achieves two close resonances approximately at 1.4 GHz and 1.7 GHz. This ability to switch between modes and cover multiple frequency bands makes the proposed design particularly well-suited for LTE-enabled mobile devices that demand wide or multi-band operation.

Abstract in English:

Abstract The increasing demand for bandwidth in modern communication networks has highlighted the need for efficient and dynamic resource allocation. Elastic Optical Networks address this challenge by enabling flexible spectrum and power assignment. This paper proposes an advanced resource allocation technique based on multi-objective optimization (MOO) to jointly optimize spectrum and power, mitigating nonlinear impairments and enhancing network performance. When a connection request arrives at the Call Admission Control, all possible frequency slot demands are generated by combining the requested bit rate with the available modulation formats. The Min Slot Continuity Capacity Loss (MSCL) heuristic selects routes and slot sets to minimize allocation capacity loss for each modulation level. From this process, a matrix of frequency slot combinations is built and subsequently explored by the MOO framework. The proposed method integrates the MSCL heuristic with power assignment to reduce spectrum fragmentation and select optimal power levels, thereby improving the optical signal-to-noise ratio. By jointly considering spectrum positioning, channel powers, amplified spontaneous emission noise, and nonlinear effects, the approach achieves significant performance gains. Simulation results demonstrate that the proposed method outperforms the Power and MSCL (P-MSCL) algorithm, achieving an approximately 11% reduction in blocking probability under a 180 Erlang load in the NSFNET topology with identical parameters.

Abstract in English:

Abstract The present research proposes a methodology to develop a model to predict Path Loss in a mixed environment comprising urban areas with tree-lined streets. Based on cross-validation and utilizing Artificial Intelligence (AI) and Machine Learning (ML) algorithms that employ various training functions, architectures, and numbers of neurons, the goal is to optimize the model’s performance in predicting Path Loss (PL) in mixed environments. The model is structured in layers, incorporating geolocation, non-line-of-sight loss, urban density, and vegetation coverage to predict PL. Within this model, Bayesian optimization is applied to select the best hyperparameters. Experimental results demonstrate its effectiveness, with a mean Root Mean Square Error (RMSE) per k-folds of 4.91 dB and Standard Deviation (STD) 4.76 dB for more forested areas.

Abstract in English:

Abstract This work investigates the optimization of silicon waveguide crossings using a hybrid GRASP-Simulated Annealing (GRASP-SA) algorithm coupled with two-dimensional finite element method (2D-FEM) analysis. An inverse design approach was adopted to systematically modify geometric parameters and enhance transmission efficiency at the design wavelength of 1.55 μm. Different values of the control parameter μ were evaluated, and the best-performing configuration was selected for further spectral analysis. The optimized structure achieved transmission efficiencies above 97%, corresponding to approximately 0.13 dB insertion loss. A wavelength sweep from 1.50 to 1.60 μm confirmed the stability of the optimized geometry. The results demonstrate that the proposed hybrid metaheuristic framework is an effective alternative for the design of high-performance photonic waveguide crossings.

Abstract in English:

Abstract This paper presents the design and experimental validation of a compact, single-layer, triple-band Frequency Selective Surface (FSS) based on triple square loops. The proposed structure targets resonant frequencies at 1.56 GHz, 2.45 GHz, and 3.50 GHz, corresponding to the GPS L1, Wi-Fi, and 5G bands, respectively. An equivalent circuit model (ECM) was developed to guide the initial parametric design, reducing reliance on computationally intensive full-wave simulations. The structure was optimized using HFSS and fabricated on a low-cost FR-4 substrate. Simulated and measured results show good agreement, with three well-defined stop bands exhibiting low insertion loss and stable resonant frequencies. Experimental measurements under oblique incidence up to 45° confirm the angular stability of the design for both TE and TM polarizations. Compared to prior works, the proposed FSS offers simpler geometry, lower fabrication complexity, closely spaced resonances with minimal frequency shift under angular variation, and low pass-band insertion losses. These features make the proposed FSS a strong candidate for compact and low-profile solutions in GPS, Wi-Fi, and 5G systems requiring multiband electromagnetic filtering.

Abstract in English:

Abstract This study proposes a wireless power transfer (WPT) system based on inductive coupling for powering implantable medical devices (IMDs). The system operates at 403MHz, within the Medical Implant Communication Service (MICS) band. It consists of two resonators utilizing split-ring loops geometry. A power transfer efficiency (PTE) of 16.58% is achieved at a transfer distance of 12mm through living tissue. The transmitter and receiver feature compact dimensions of 25mm × 25mm × 1.52mm and 14mm × 14mm × 1.27mm, respectively. These are among the smallest dimensions reported for resonators based on planar split-ring loop geometry. Electromagnetic (EM) simulations were performed to optimize the geometry for maximum efficiency while maintaining reduced dimensions at a 12mm transfer distance. According to simulation results, the maximum received power, limited by specific absorption rate (SAR) regulations, reaches 105.5mW at 8mm and 29.44mW at 12mm. The resulting compact size and level of maximum received power are sufficient to enable integration within implantable medical devices such as cardiac pacemakers, cochlear implants, and certain neurostimulators.

Abstract in English:

Abstract This paper presents an analytical method for designing FIR filters based on the hardware of time-delayed photonic neural networks for chromatic dispersion compensation in long-reach passive optical networks. The model employs a Fourier-based synthesis of the compensation function, allowing for the closed-form determination of phase and amplitude weights for each optical path. Different implementation strategies are considered, including solutions with phase-only control and others with additional amplitude control using tunable attenuators. Simulations over a 100 km standard single-mode fiber link demonstrate effective dispersion compensation for NRZ-OOK signals. In particular, the symmetric FIR-based design with 23 optical paths and 25 ps delay spacing achieved BER < 10-3 at data rates up to 40 Gbps under amplified spontaneous emission noise. These results confirm the analytical approach's potential to provide scalable, power-efficient, and high-speed solutions for future long-reach optical access networks.

Abstract in English:

Abstract As a simulation-based exploratory study, a novel and improved dual-mode resonator is proposed in this paper. By exploiting two asynchronous resonance modes that can be generated within the proposed resonator, such architectures can be utilized to construct dual-band filters. In addition, the new cavity introduces an anti-resonance mode that can be used to create a transmission zero within the rejection band of dual-band filters, thereby enhancing filter selectivity while maintaining a simple inline filter structure. The simulation results demonstrate an improvement in the quality factor and a reduction in the overall resonator size compared to conventional designs, while preserving the characteristic impedance at the two resonance frequencies. Furthermore, the quality factors of the modes and the anti-resonance frequency remain stable as the resonance frequencies vary. Based on this novel resonator, the design of a dual-band filter is presented, starting from the equivalent circuit and coupling configuration to the complete filter synthesis methodology, including the determination of the coupling matrix. A tenth-order dual-band filter is designed to validate the proposed concept. The simulation results indicate that the filter meets the required specifications for both passband widths and center frequencies.

Abstract in English:

Abstract The article presents a design optimization method for microwave resonators. This method is based on the development of an artificial neural network (ANN) to calculate the physical parameters of resonators used in microwave resonators, which results in resonator characteristics according to the operating frequency requirements of the design. The proposed approach uses a resonator with a T-inverted geometry as the basis for modeling and validating the artificial neural network. The designed resonator is manufactured and measured according to the physical parameters provided by the network. The results obtained from the simulations of the resonator designed by the proposed method and the measurements show good agreement. For the provided examples, the prediction error of the model reaches 2.55%, indicating an accuracy of over 97%, confirming the validity of the proposed approach.

Abstract in English:

Abstract This paper presents the development and experimental validation of a low-cost Direction of Arrival (DoA) estimation system using Software-Defined Radio (SDR) technology. The system employs an NI USRP B-210 with two printed log-periodic dipole antennas in a coherent configuration, implementing beamforming algorithms through GNU Radio software. Experimental validation was conducted in different environments at 3 GHz across a ±90◦ range. The system maintains accurate DoA estimates with interference levels up to 8 dB below the signal of interest. Performance limitations include front-back ambiguity inherent to two-element arrays and sensitivity to multipath effects. This work demonstrates the feasibility of replacing expensive commercial DoA systems with affordable SDR-based alternatives, with advantages such as easy deployment and reconfigurability.

Abstract in English:

Abstract Climacteric fruit respiration generates carbon dioxide (CO2), making its real-time monitoring crucial for optimizing storage and transport conditions, minimizing economic losses and waste. This work demonstrates the application of Wavelength Modulation Spectroscopy (WMS) for the development of a sensor capable of measuring CO2 concentration in real time with high precision and reproducibility. For the technique, a Distributed-Feedback diode laser was used, tuned to the 1572.3 nm CO2 absorption line. The temporal evolution of CO2 concentration released by tomato and banana at different ripening stages was measured. The sensor exhibited a detection limit for CO2 variations ranging from 122 to 488 parts per million (ppm). The results demonstrate the applicability of WMS for monitoring fruit respiration. The normalization technique second harmonic/first harmonic (2f/1f) proved essential for mitigating thermal effects, as the 1f signal corrects for laser power and non-absorption losses, thus enhancing data reliability. Analysis of CO2 evolution curves suggests the potential to study gas diffusion phenomena within fruits, evidenced by the sigmoidal profile. This sensor has potential for future applications in modified atmosphere packaging (MAP) and quality control.