Abstract in English:

Abstract This paper investigates the influence of a finite-sized ground plane, on the performance characteristics of a symmetric compressed-V dipole antenna (CVDA), of interest to wireless communications in unmanned surface boats. An existing method of moments (MoM) formulation of the CVDA problem is extended to include an account for the ground plane, modeled as a wire-grid structure. Essentially, two key antenna performance assessment parameters are examined in the paper. First is the return loss profile; primarily in order to interrogate how input impedance is affected by the absence of a balun, typically utilized in the feed network of symmetrical wire antennas, fed through coaxial cables. And second is the far field pattern, characterized in this case, by two orthogonal field components in the E- and H-planes, for which a special case of partial directivity (and hence polarization efficiency) is applicable. Computational results obtained and extensively discussed in the paper clearly demonstrate the influence of the finite ground plane on CVDA performance parameters. As an example, compared to a maximum return loss value of 26.6 dB for CVDA in the absence of the ground plane, a maximum value of about 42 dB was recorded for the CVDA with a ground plane size specified by an aspect ratio of 2.

Abstract in English:

Abstract This paper presents a reconfigurable frequency-selective surface (FSS) featuring switchable reflection and transmission characteristics based on a complementary-inspired four-arm star geometry. The design process begins with the independent analysis of a slot element and its complementary patch counterpart, which are subsequently integrated on a single-layer substrate. To enable electrical reconfigurability, the patch element is modified by adding a switching point to integrate a PIN diode along with bias lines for feeding. The electromagnetic response is evaluated across three diode operational states: off (reverse bias), on (forward bias), and threshold bias. For TE polarization, the structure exhibits a singlepassband response near 3.75 GHz in the reverse-biased state and a dual-passband response near 2.1 GHz and 6.9 GHz in the forwardbiased state, with a stopband between the two passbands. At the threshold voltage, the reconfigurable complementary FSS provides an attenuated-transmission state, enabling control of the transmitted signal level. These operating modes allow the same surface to switch between transmission, rejection, and attenuation, which is useful for adaptive filtering, interference mitigation, and signallevel control in intelligent 5G-Advanced communication network applications.

Abstract in English:

Abstract A miniaturized planar log-periodic dipole antenna (PLPDA) with 227×106 mm printed on an FR4 substrate is presented. The antenna operates over a frequency range from 1 GHz to 6 GHz, and suitable for the direction of arrival (DOA) estimation using handheld spectrum analyzer. A combination of meandered lines and fan-shaped loading is employed to miniaturize the PLPDA size while optimizing the antenna structure and dimensions. The antenna is fed by a single-coaxial balun, in which the coaxial outer conductor is soldered to the narrow top boom, while the inner conductor is connected to the wide bottom boom. The proposed miniaturized PLPDA (MPLPDA) were designed and simulated by Ansys HFSS 2023 R1, and the fabricated MPLPDA is tested in an anechoic chamber. Benchmarked against the conventional PLPDA presented in the literature, the fabricated MPLPDA achieves an approximately 16.5% reduction in antenna width with no significant performance degradation, while delivering gain ranging from 3.43 dBi to 8.18 dBi across 1 GHz to 6 GHz band which VSWR was almost below 2.

Abstract in English:

Abstract The propagation of high-frequency signals in forest environments is a topic of great interest. Several works address formal solutions in their frameworks, using various types of approaches. This paper revisits the subject using a proposal derived from Norton’s solution, as alternative for simplifying the expression for calculating the electric field inside forests. The final expression shows the main mechanisms associated with propagation in this environment, producing a simplified expression with low computational cost. A campaign of measurements was carried out to validate the model.

Abstract in English:

Abstract This paper presents a Flexible Multiband Textile Antenna (FMTA) for wearable Sub-6 GHz applications, inspired by an antique keyhole design and fabricated on a denim substrate with a dielectric constant of 1.7. A rectangular slot and Defected Ground Structure (DGS) are incorporated to achieve triple-band operation covering the 3GPP-standard-compliant n40 (2.3 GHz), n79 (4.5 GHz), and n47 (5.9 GHz) bands. The proposed antenna provides an 860 MHz impedance bandwidth in the n79 band, exceeding the 3GPP requirement of 600 MHz and demonstrating enhanced wideband performance. These operating bands support high-capacity 5G communications and Vehicle-to-Everything (V2X) applications in intelligent transportation systems. The antenna exhibits stable radiation characteristics, good impedance matching, and satisfactory gain under both flat and bent conditions. Furthermore, the maximum Specific Absorption Rate (SAR) is 0.799 W/kg, which is well below the recommended safety limits, confirming its suitability for wearable applications. The fabricated prototype shows good agreement with the simulated results, validating the effectiveness of the proposed design.

Abstract in English:

Abstract This study introduces a new methodology for modeling the nonlinear behavior and the magnetic anisotropy of ferromagnetic materials. The proposed approach was adapted from models used to represent population growth based on Logistic-type functions. For the purposes of this paper, the model was adapted to describe magnetic induction under an imposed magnetic field, taking into account the magnetic anisotropy present in grain-oriented electrical steels. The following results demonstrate that magnetic anisotropy can be accurately modeled using a set of parameters obtained from polynomial functions as a function of the excitation angle. The model was validated by comparing calculated and experimental data.

Abstract in English:

Abstract This paper proposes a dual-band circularly polarized (CP) antenna that uses a metasurface. A diagonal corner cut square-shaped patch antenna with two notches is used as the driven antenna. The metasurface uses 3 × 4 rectangular elements of different sizes that are arranged non-uniformly, and symmetrically along the vertical axis. By optimizing the parameters of the proposed antenna, an impedance bandwidth of 42.00% (5.25-8.05 GHz) and dual-band 3 dB axial ratio bandwidth (ARBW) of 2.85% (5.18-5.33 GHz) and 9.40% (6.78-7.45 GHz) at two frequency bands are obtained. The peak gains at the two CP bands are found to be 7.19 dBic and 5.75 dBic, respectively. The size of the antenna is 35 × 35 × 3.04 mm3. I-Tera MT40 laminate material is used as a substrate for the prototype fabrication. Simulated results and the results measured experimentally are in good agreement.