Abstract In this paper, we present a novel numerical model for simulating partial discharges (PDs) transient currents excited by high-voltage DC (HVDC) systems. The model is based on the telegraph equations, which are solved in the time domain via the finite-difference method (FDM). With the proposed model, one can simulate air ionization through its distinct phases based on the electric field’s magnitude. This study specifically provides effective electrical conductivity of ionized air over time and space, calculated in the discharge channel also as a function of voltage and gap distance in a needle-plate setup. Validation is performed against experimental results from our laboratory experiments, demonstrating agreement despite the model’s one-dimensional nature. The simplicity of the model leads to much smaller simulation times (up to two minutes) compared to more complex three-dimensional models (typically requiring hours to complete), highlighting its potential for efficient PD analysis and future developments of general PD models based on effective plasma conductivity.

Abstract In this paper, it is presented a general optimization methodology for improving empirical models predicting Okumura-Hata, Cost-231, ECC-33, and Egli using Genetic and Differential Evolution Algorithms. The methodology was tested using georeferenced signal power samples from Uberlândia, Brazil, for a television channel operating at 569.142857 MHz. Each parameter of the model formulas was adjusted with a variable optimized by the algorithms. A significant innovation was the inclusion of an altitude parameter weighted by an optimized coefficient, which notably enhanced the prediction accuracy. The primary contribution of this work is the development of a set of analytical equations derived from the proposed methodology, eliminating the need for computational power to estimate path loss for the evaluated models in the area in question. The performance of these equations was assessed using the Mean Squared Error (MSE) metric, demonstrating improvements of up to 92.03% over standard models, contingent on the empirical model and optimization algorithm applied.

Abstract Space-fed array comprising of E-shape or U-slot cut rectangular microstrip antennas using the modified feed designs are proposed for higher gain and wider bandwidth. Modified feed optimally illuminates the edge space-fed elements to achieve a maximum gain. Amongst the two space-fed array variations, 7 x 7 E-shape space-fed array, excited using the feed comprising of gap-coupled and stacked E-shape patches provides bandwidth and gain of 2.085 GHz (48.97%) and 18.5 dBi, respectively. The antenna exhibits broadside radiation pattern across the complete bandwidth. An experimental validation has been carried out for the simulated results that show a close agreement.

Abstract This study investigates the effectiveness of employing Planar Transmission Lines (PTL) with stubs to determine the water content in transformer oils. The research aims to elucidate how transmission responses along the line can provide valuable patterns for oil characterization. Notable results were achieved, particularly in identifying representative frequencies for each range of S21 scattering parameters, enabling the derivation of well-fitted linear expressions for the data. These findings suggest promising potential for the practical application of this approach. This study contributes not only to the understanding of the proposed technique but also to the stimulation of subsequent research aiming to enhance and consolidate this analytical methodology.

Abstract In this study, we developed a Radio Frequency Identification (RFID) sensor to monitor respiratory rates. The sensor utilizes a passive RFID tag enhanced with a metamaterial-inspired structure to boost its maximum gain value. This gain increased from -0.39 dBi to 0.57 dBi. Monitoring of the respiratory rate was conducted by analyzing variations in the Received Signal Strength Indicator (RSSI), which were influenced by respiratory movements. The RSSI data collected from the RFID tag readings were processed using the Daubechies wavelet of order 5 (db5) with three levels of signal decomposition, resulting in signals with reduced noise. These measurements were particularly effective when the participant was at rest, with the RFID tag positioned over the abdomen. The maximum reading range obtained was 1.04 m. The respiratory rates derived from the RSSI variations were validated against a vital signals monitor, confirming that they fell within the expected frequency variation range of the multiparameter monitor.

Abstract In this work a broadband Magnetoelectric (ME) dipole antenna for the Global Navigation Satellite System (GNSS) applied to nanosatellites is proposed. The antenna consists of a reflective cavity with open walls containing four gaps to enhance the axial ratio (AR) bandwidth. Additionally, it includes two ME dipoles formed by two pairs of vertical and horizontal copper plates, one of which is trapezoidal and a T-Γ-shaped cross-feeding structure. A prototype was designed and subsequently manufactured and measured. The experimentally obtained results exhibit consistent agreement with simulated outcomes, demonstrating that the antenna has a wide impedance bandwidth of 111.36% from 1.13 GHz to 1.62 GHz for the Voltage Standing Wave Ratio (VSWR) ≤ 2 and a 3 dB AR bandwidth of 120.45% from 1.10 GHz to 1.63 GHz. Within this range, high gain (≥8.5 dBi) and high radiation efficiency (90%) can be achieved. Furthermore, the antenna exhibits right-hand circular polarization (RHCP) and possesses good unidirectional radiation characteristics with a high front-to-back ratio (≥ 20 dB). (ME GNSS (GNSS proposed (AR Additionally plates TΓshaped T Γ shaped crossfeeding cross feeding structure measured outcomes 11136 111 36 111.36 113 1 13 1.1 162 62 1.6 VSWR (VSWR 12045 120 45 120.45 110 10 163 63 range ≥8.5 85 8 5 (≥8. dBi 90% 90 (90% achieved Furthermore righthand right hand RHCP (RHCP fronttoback front back ≥ ( dB. . dB) 1113 11 111.3 1. 16 6 1204 12 4 120.4 ≥8. (≥8 9 (90 111. 120. ≥8 (9

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. multipump multi Telluritebased Tellurite based multipumped pumped dimensions 25 2 5 2. 152 160 nm W 1 16

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. highselectivity high selectivity substrateintegratedwaveguide substrate integratedwaveguide (SIW proposed twolayered layered resonator layer simultaneously controlled demonstration measured S11 S |S11 10 -1 89 8 9 8.9 3.864.23 386423 3.86 4.23 3 86 4 23 (3.86-4.2 GHz , GHz) 608 6 08 6.0 405 05 4.0 37 7 3. 43 4. 519 5 19 5.1 respectively outofband out band 15 33 dBGHz dB/GHz S1 |S1 1 - 8. 864 3.864.2 38642 386 3.8 423 4.2 2 (3.86-4. 60 0 6. 40 51 5. |S 3.864. 3864 38 42 (3.86-4 3.864 (3.86- (3.86 (3.8 (3. (3 (

Abstract This paper presents a novel nature-inspired tri-band frequency selective surface (FSS) characterized by closely spaced bands, angular stability, and polarization independence. The FSS element adopts a segmented Fibonacci spiral geometry. While a single-segmented Fibonacci spiral does not inherently possess polarization independence, the proposed proof of concept achieves this by cascading the same design geometry rotated by 90° between them. Resonant frequencies of 1.63 GHz, 2.46 GHz, and 3.43 GHz are achieved, with minimal separation ratios of 1.5 from the second to the first frequency and 1.4 from the third to the second. Additionally, angular stability is confirmed up to 45°. Simulation of the FSS is conducted using HFSS software, and the simulated results are rigorously validated against experimental data, demonstrating excellent agreement. natureinspired nature inspired triband tri band (FSS bands independence singlesegmented single 90 them 163 1 63 1.6 246 2 46 2.4 343 3 43 3.4 achieved 15 5 1. 14 4 Additionally 45 45° software data agreement 9 16 6 24 2. 34 3.

Abstract The equivalent wave impedance circuit model (ECM-WI) is presented for the analysis of frequency selective surfaces (FSS). The development of the analytical model is based on homogenization theory, as well as analogies between wave theory and transmission line theory. The coplanar strip model and the concept of wave impedance are used to scale the Marcuvitz model for periodic strip gratings of conductive strips, as well as to consider the influence of the presence of a lossy dielectric substrate on the frequency response of the FSS. In particular, the model is applied to the analysis of square loop FSSs and considering the normal incidence. The results obtained are presented by comparing full-wave simulations for the two proposed models, obtaining average deviations in absolute values (%) of 2.11 and 0.38 for resonance frequency and 3.45 and 5.49 for bandwidth. The prototype manufactured in FR-4 obtained a deviation of 2.56% for resonance frequency and 2.79% for bandwidth. ECMWI ECM WI (ECM-WI FSS . (FSS) strips particular incidence fullwave full models % (% 211 2 11 2.1 038 0 38 0.3 345 3 45 3.4 549 5 49 5.4 bandwidth FR4 FR 4 FR- 256 56 2.56 279 79 2.79 (FSS ( 21 1 2. 03 0. 34 3. 54 5. 25 2.5 27 7 2.7

Abstract This paper proposes a methodology for developing antipodal Vivaldi antennas using RSIW (Ridge Substrate Integrated Waveguide) technology for a specific cut-off frequency. The technique employs metallic-vias and metalized cylindrical posts of reduced sizes inserted in the dielectric substrate. The simulations were performed using the ANSYS® Electronics Desktop software. The antenna RSIW is designed for a resonant frequency of 4 GHz and was fabricated on FR4 (ɛr=4.4 and tanδ=0.02). The structure is compared to an antipodal Vivaldi antenna (AVA) fed by a SIW. The structure proposed had an increase in bandwidth of 4.09 GHz and an increase in gain of 1.41 dBi. Ridge Waveguide cutoff cut off metallicvias metallic vias substrate ANSYS software FR ɛr=4.4 ɛr44 ɛr (ɛr=4. tanδ=0.02. tanδ002 tanδ tanδ=0.02 . 0 02 tanδ=0.02) AVA (AVA SIW 409 09 4.0 141 1 41 1.4 dBi ɛr=4. ɛr4 (ɛr=4 tanδ00 tanδ=0.0 40 4. 14 1. ɛr=4 (ɛr= tanδ0 tanδ=0. ɛr= (ɛr tanδ=0 tanδ=

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. paper ML (ML parts first prediction then MLP (MLP PDP. PDP . 240 vegetation (OLS (RMSE 039 0 39 0.3 (PDP 24 03 3 0. 2

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. SplitStep Split Step SSWPE SSW PE (SSW-PE presented innovations narrowangle narrow angle approaches WAPE respectively Furthermore variations representation conditions aspects algorithm wavelets wellestablished well established solutions DMFT (DMFT SSPE (SSPE method conducted simulations Thus methodology

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. Tshaped T shaped bandstop band (BSF cutoff cut off matrices up 11 1. pF untuned un tuned (un-tuned 1047 047 1.04 dB 36 3dB bandwidth MHz closely structures 104 04 1.0 3 10 0

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. AFSS (AFSS systems Initially FR4 FR 4 FR- 102 10 2 10. 153 1 53 1.5 switching state off. . off) 08 0 8 0. 25 5 2. surface software coefficients performed agreement 15 1.