This article is a result of measuring the dielectric constant of a dielectric used in studying the influence of dielectrics on the antennae reflection coefficients. A paper having a density of 0.797 g/cm3, moisture content of 0% and temperature of 210C, is used as a dielectric. Although the literature provides a lot of data on the dielectric properties of wood and paper, without direct measurement of the dielectric constant it is impossible to know its amount for the dielectric used in the defined frequency range. Dielectric constant measurements are performed in the frequency range from 100 Hz to 100 kHz, while the frequency range of its impact on the aperture antenna reflection coefficients is up to 2 GHz. The frequency range from 100 KHz to 10 GHz is interpolated and fitted by using measurements and available literature data and by respecting physical influences and phenomena and functional changes of the dielectric constant of paper within the given range

In this article, an aperture antenna excited by a waveguide with a circular cross-section and covered with a dielectric plate was analyzed via simulation calculation and verified via measurements. The influence of the geometrical and electromagnetic parameters of the dielectric plate on the reflection coefficient S₁₁ of the antenna opening was systematically analyzed. The geometrical parameters taken in this analysis are the thickness d and the width/length h₁/h₂ of the dielectric plate. The electromagnetic parameters used in this analysis are the real and the imaginary part of permittivity (ε_r, tan δ) and the electrical conductivity of the dielectric plate (σ). The simulation calculation and analysis included other structural and electromagnetic parameters of the dielectric plate (density of the radome material, relative permeability, and magnetic loss tangent (ρ, µ_r, and tan δ_µ, respectively)), but the results show that in the range of real values of these parameters for the materials used for the dielectric plate, they had no significant influence on the reflection coefficient. The results show that impedance-matched antennas with very low values of the reflection coefficients S₁₁ at the resonant frequency can be realized by changing the geometrical and electromagnetic parameters of the dielectric plate material. The results are presented for a circular aperture antenna on a planar grounded plane with a dielectric plate on the opening, and the achieved lowest values of the S₁₁ parameter were −45.17 dB (simulated) and −43.93 dB (measured) at the frequencies of 1.7820 GHz and 1.7550 GHz, respectively. The estimated values of the dielectric plate parameters in this case are thickness d = 11.08 mm (0.67 λ); width × length of grounded plane and dielectric plate h₁ × h₂ = 423 × 450 mm² (2.51 × 2.67 λ); relative permittivity 2.5, tan δ = 0.09, μ_r = 1, tan δ_μ = 0.00, ρ = 1200 kg·m⁻³; and electrical conductivity σ = 0 S/m. The simulation calculation results were verified by measuring the reflection coefficient S₁₁ on the created laboratory model of the aperture antenna with the dielectric plate and showed a very good match.

Conventional magnetically coupled resonant wireless power transfer systems are faced with resonant frequency splitting phenomena and impedance mismatch when a receiving coil is placed at misaligned position. These problems can be avoided by using uniform magnetic field distribution at receiving plane. In this paper, a novel 3D transmitting coil structure with improved uniform magnetic field distribution is proposed based on a developed optimization method. The goal is to maximize the average magnetic field strength and uniform magnetic field section of the receiving plane. Hence, figures of merit (FoM₁ and FoM₂) are introduced and defined as product of average magnetic field strength and length or surface along which uniform magnetic field is generated, respectively. The validity of the optimization method is verified through laboratory measurements performed on the fabricated coils driven by signal generator at operating frequency of 150kHz. Depending on the allowed ripple value and predefined coil proportions, the proposed transmitting coil structure gives the uniform magnetic field distribution across 50 to 90 of the receiving plane.

The aim of this research was to determine the efficiency of electromagnetic (EM) radiation absorbers based on biomaterials from harvest residues (soybean straw, wheat straw, and clover straw) for the additional protection and/or construction of residential buildings. To determine their protective properties, the transmission parameter S₂₁ was measured through harvest residues in the frequency range from 300 MHz to 5 GHz. Important parameters of the tested samples included sample type, sample thickness, and humidity. The measurement results showed that the transmission parameters decreased with an increase in the sample thickness, moisture, and frequency. Regarding this type of substrate, soybean straw showed the lowest values of parameter S₂₁ for all measurements except for the case of the highest amount of moisture (34.48%), for which clover straw showed the lowest value of the transmission parameter. The greatest reduction in the S₂₁ transmission parameter was 43.80 dB for a soybean sample of 300 mm thickness at a frequency of 4.93 GHz. These tests were performed on samples that were not additionally structured (additives, pressing, additional shredding, etc.), so it was possible to optimize their structure and conduct further research.

This paper presents the results of a study of radio wave propagation in underground wine cellars in the context of the optimal use of wireless communication systems for the application of the Internet of Things (IoT) in wine production environments. Electric field strength measurements were carried out in two subterranean line-of-sight (LOS) and non-line-of-sight (NLOS) conditions at 860 MHz, 2400 MHz, and 3600 MHz. The measured results were compared with predictions from seven existing propagation models, including site-general models (Free-space, ITU-R P.1238-13, ITU-R P.1411-12, ETSI TR 138 901 V16.1.0) and site-specific models (ITU-R P.1411-12, tunnel and knife-edge diffraction). Statistical analysis determined that the ITU-R P.1238-13 model, which estimates path loss in corridors, and the tunnel model have the best agreement with measurements in LOS conditions, with average Root Mean Square Error (RMSE) values of 2.8 dB and 3.56 dB, respectively. For the NLOS regions, the knife-edge diffraction model achieved the highest accuracy (average RMSE = 2.77 dB). Furthermore, based on the measurement results, the coefficients of the general path-loss model were adjusted to the data using the least-squares method, yielding RMSEs of 2.02 dB for LOS and 2.65 dB for NLOS conditions. The analysis showed that combining the ITU-R P.1238-13 or tunnel model for LOS conditions with a diffraction-based model for NLOS conditions provides a good basis for modeling radio propagation in subterranean wine cellars. These findings support the design of efficient and robust IoT communication networks in winery environments.