Resumen en Inglés:

Abstract This work presents a numerical analysis of a multilayer graphene-based absorber, composed of SiO₂, graphene, and metals (Ag, Au). The device structure is SiO₂/Graphene/SiO₂/metal, each material significantly influencing optical properties. The model, insensitive to the relaxation rate, exhibits high response time, beneficial for high-performance all-optical communication devices, resonators, and perfect absorbers. SiO₂ provides a stable, transparent dielectric base for wave propagation. Various Kubo formula references for graphene's conductivity were examined. Resonances were analyzed using different Ag and Au data sets from Rakic, Johnson, and Palik. The results demonstrate that the interaction of these components is crucial for realistic simulations aligned with experimental data.

Resumen en Inglés:

Abstract Nonuniform Large Antenna Arrays (NULaA) represent a possible approach for 5G and forthcoming wireless communication technologies. This comprehensive study analysed NULaA geometry, performance benefits, and drawbacks in 5G applications. Compared to uniform arrays, NULaA feature better beamforming, less mutual coupling, and higher spectral efficiency. The uneven spacing of antenna elements allows for more array design flexibility, better sidelobe suppression, spatial resolution, and power efficiency. Linear, circular, planar, fractal, and sparse NULaA geometries were evaluated to determine their suitability for 5G applications. NULaA offer enhanced spatial selectivity, less interference, and tiny designs for urban applications, according to this review. NULaA introduce complex optimisation processes, calibration and maintenance challenges in large deployments, and economical considerations connected to bespoke designs and sophisticated production methods. Current research trends and future directions highlight AI-driven optimisation, new materials, and NULaA' integration with other 5G technologies. Feature Selective Validation (FSV) is applied to selected references with simulated and measured results, yielding Good to Excellent agreements (GDM < 0.32), confirming NULaA's performance superiority. This review sheds light on how NULaA will shape wireless communication and 5G networks.

Resumen en Inglés:

Abstract A lower cross polarization level in the radiation pattern of microstrip antenna is needed for achieving the pattern and polarization purity. The main source of cross-polar radiation in microstrip antenna is the residual contribution of higher order resonant modes present at the fundamental resonant mode frequency. In this paper, designs of circular microstrip antenna either loaded with ground plane 900 Sectoral slots or shorting posts placed on the patch or the combination of slots and shorting posts, are proposed for the cross-polar level reduction at the fundamental mode. These techniques increase the spacing of TM21 mode frequency with respect to TM11 mode that achieves reduction in the cross-polar levels. Amongst all the techniques presented, design with five shorting posts yields cross-polar reduction by 48 dB in the broadside direction, whereas combination of shorting posts and 900 Sectoral slots achieves 45 dB cross-polar reduction against the circular patch employing the conventional square ground plane. An experimental validation for the simulated results has been carried out that shows a closer agreement.

Resumen en Inglés:

Abstract Mutual coupling poses a significant challenge in compact MIMO antenna systems because it lowers isolation, radiation efficiency, and diversity performance. This paper presents a compact frequency selective surface (FSS) technique to effectively reduce mutual coupling between closely spaced antenna elements that are 0.117λ0 apart. The designed FSS changes the polarization of incoming waves, which minimizes surface current interactions and enhances port isolation. We analyze the antenna performance using full-wave simulations and experimental measurements in the 2-5 GHz band. The results show a coupling reduction of 16-38 dB and excellent diversity characteristics, including ,ECC < 0.0017, TARC < -12.1413 dB, CCL < 0.0074 bit/s/Hz, MEG < -5.0567 dB, and DG> 9.99973 dB, and a radiation efficiency of 96.71%. The proposed structure demonstrates stable radiation behavior with improved isolation, confirming its potential for practical use. Due to its compact design and high isolation, this FSS-integrated MIMO antenna is a promising solution for modern high speed wireless communication systems.

Resumen en Inglés:

Abstract This study examines the interaction between millimeter waves (mmWaves) and human skin by combining Fresnel equations with the complex Cole-Cole model for relative permittivity (ɛ*), providing a realistic representation of biological tissue. The approach is novel and has not been previously applied in this context. Analyses at 24, 35, 40, 60, 77, and 94 GHz show that reflection power at normal incidence decreases from about 48% at 24 GHz to 37% at 94 GHz due to the tissue’s frequency-dependent dielectric behaviour. The pseudo-Brewster angle, derived from complex ɛ*, identifies the condition of minimal reflection for parallel-polarized mmWaves and decreases with increasing frequency, matching theoretical expectations. At 40, 60, 80, and 100 GHz, the Cole-Cole-based pseudo-Brewster angles (76°, 75°, 74°, and 73°) and corresponding reflection coefficients (0.061, 0.054, 0.043, and 0.03) closely align with experimental reports in the literature, in the 60°-80° range. Unlike the simplified lossless model predicting zero reflection at the Brewster angle, this complex ε* approach captures realistic tissue loss and dispersion. At angles beyond the grazing-incidence threshold, most mmWave energy is reflected with negligible penetration. Since skin’s refractive index (n₂>n₁≈1), total internal reflection cannot occur. Hence, “grazing-incidence threshold” more accurately describes the observed behaviour.

Resumen en Inglés:

Abstract This paper introduces an alternative design approach of a reconfigurable dual mode/dual band medium power amplifier for modern mobile communication systems. The switching process between the two bands is achieved by single pole double throw (SPDT) PIN diode switch circuits. These circuits are employed to separate and route input signals in the desired mode and band. The simulation results of the SPDT switch circuits indicate low insertion loss, reduced return loss, and high isolation over the two desired frequency bands. The two sub-band power amplifiers are designed based on class E and inverse class E modes using a commercial GaAs pHEMT device to operate at two frequency bands centered at 900 MHz and 1800 MHz, respectively. The amplifier circuit was constructed on a low cost FR4 substrate and tested experimentally. At 900 MHz, the reconfigurable power amplifier provides a drain efficiency of 65.9%, power added efficiency of 60.2%, power gain of 9.66 dB and output RF power of 22.66 dBm with input power level of 13 dBm, while at 1800 MHz the amplifier provides a drain efficiency of 60.4%, power added efficiency of 54.5%, power gain of 8.3 dB and output RF power of 21.3 dBm.

Resumen en Inglés:

Abstract In this work, polynomial regression was used for prediction of the first and second resonance frequencies, first and second cut-off frequencies at -3 dB of planar bandstop filters based on matryoshka geometry, considering the S21 curve and given certain constraints. The results were validated, considering the mean absolute error (MAE) and the mean absolute percentage error (MAPE) in the test data, calculated for each output variable. The higher values observed were 0.023 GHz for MAE and 2.30% for MAPE. Further validation was performed in new independent test data, which also showed good values for MAE and MAPE. A prototype of a filter was fabricated, and the simulated and predicted results agreed with the measured ones.

Resumen en Inglés:

Abstract In the study of Electromagnetic Compatibility (EMC) for electric vehicle motor drive systems, the simulation and prediction of conducted Electromagnetic Interference (EMI) require consideration of uncertainty factors. The application of uncertainty analysis methods within this system can effectively enhance the reliability of simulation model predictions. Due to its enormous computational cost, the commonly used Monte Carlo Method (MCM) is often impractical for engineering applications. This paper introduces two representative high-efficiency uncertainty analysis methods, the Stochastic Collocation Method (SCM) and the Kriging method, into the simulation study of conducted EMI in this system, comparing their performance from multiple perspectives. By comparing simulation results, it can be found that under the premise that the time costs required by the two methods are similar, SCM can better reflect data fluctuations. Additionally, the Mean Equivalent Area Method (MEAM) is employed to evaluate the analysis results. Of these, the SCM evaluation results are above 0.9, while the Kriging method falls below 0.85. In the simulation of this system, SCM has better applicability. This study provides a method support for the EMC optimization design of an electric vehicle motor drive system considering uncertainty in practical engineering applications.

Resumen en Inglés:

Abstract A novel design of an Ultra-wideband (UWB) antenna based on a grounded coplanar waveguide element, featuring an edge engraved square patch antenna is proposed. This antenna configuration integrates a square patch with carved corners as the primary radiating element, along with coplanar waveguide components and Frequency Selective Surface (FSS) elements. The coplanar waveguide elements and carved corners serve to enhance both impedance matching and radiation directivity in this prototype. To further augment gain, an 8×8-unit cell is positioned beneath the antenna. The FSS component is constructed through a combination of square and circular structures. The optimized dimensions of the proposed antenna measure 40×40×1.6 mm3, utilizing FR4 substrate material. Experimental validation confirms the performance of proposed design, with simulation outcomes closely reiterate measured results. The antenna exhibits resonant characteristics throughout the ultra-wideband frequency range of 1.9-14.4 GHz. The proposed edge-engraved square patch antenna exhibits a fractional bandwidth of 153.3% and a maximum efficiency of 96%, while the incorporation of FSS elements provides an average gain enhancement of 4 dBi and a peak gain of 9.6dBi observed across the UWB range.

Resumen en Inglés:

Abstract This paper presents an analytical and design-oriented enhancement of the cascaded single-stage distributed amplifier (CSSDA) aimed at improving its gain-bandwidth performance. The proposed approach, referred to as the Enhanced Cascaded Single-Stage Distributed Amplifier (ECSSDA), is based on leaving the input artificial transmission line of the CSSDA open-circuited. This configuration leads to a theoretical 6 dB gain increase at low frequencies due to voltage doubling at the gate of the first stage but also introduces input mismatch and frequency-dependent gain behavior. To overcome these limitations, the transducer gain of the ECSSDA is analytically derived and approximated using Chebyshev polynomials. This approximation can be interpreted as an impedance-shaping technique that stabilizes the frequency response and limits gain ripple up to the cutoff frequency. Circuit-level simulations demonstrate a broadband gain improvement of approximately 7.24 dB and a bandwidth extension of about 3 GHz compared to the conventional CSSDA, while maintaining acceptable matching conditions. Since the proposed method relies on normalized parameters, it can be extended to other transistor technologies and distributed amplifier implementations.