A method for enhancing the adhesion properties of polytetrafluoroethylene (PTFE) surfaces is presented. The approach employs a fast neutrals flow generated by a DC glow discharge plasma with a grid neutralizer. Low power levels (≈6 W) provided by the stable DC discharge prevent physical sputtering and surface damage, while strong UV radiation from pure argon promotes efficient defluorination. The choice of working gas composition, discharge parameters, and treatment duration was informed by plasma emission spectroscopy, water contact angle (WCA) measurements, and systematic optimization. The combined effect of low-energy neutral particles and UV radiation leads to a significant increase in surface energy to 82 mN/m and a reduction in WCA to 13∘, confirming the effectiveness of the proposed method. Thanks to its simplicity, scalability, and reliability, the method holds significant potential for industrial applications.

The article proposes a method for calculating the effective permittivity of a material with periodically distributed inhomogeneities. The method is based on the calculation of the equivalent electrical circuit of a unit cell of the material. To conduct experimental studies using three-dimensional DLP printing, samples of material with cylindrical air cavities of various diameters were manufactured. Comparison of the results of calculation and measurement of the effective dielectric constant showed a small divergence (up to 5%).

The design of a reflector for the formation of millimeter waves with electrically tunable orbital angular momentum (OAM) is presented. The reflector is based on ferroelectric (FE) ceramic. The principle of operation of the device is described and the relations for calculating the design elements are presented. The proposed structure offers several advantages: compact dimensions, a wide operating frequency range up to 100 GHz enabled by the intrinsic properties of FE, and the ability to electrically reconfigure the OAM mode. The tunability factor of the FE material was experimentally measured and used during reflector simulations. The magnitude and phase distributions confirm the formation of a nonzero OAM mode at 60 GHz. The electric field distribution was analyzed for different incidence angles from the source antenna. The proposed device can be used in millimeter-wave wireless communication systems, particularly in non-line-of-sight (NLoS) scenarios.

A fast-neutral flux generated from a glow gas discharge using a custom-designed source has been proposed to improve the adhesion of PTFE surfaces. The effects of glow discharge parameters and the composition of the working gas on the activation process were evaluated through contact angle measurements and subsequent surface energy calculations. PTFE surfaces treated in an argon atmosphere exhibited the most significant hydrophilic and adhesive properties, achieving a water contact angle as low as 13∘ and surface energy values of 82 mN/m, with an exceptionally high polar component. The optimal effect was observed when the optical spectrum of the plasma showed maximum intensity peaks in the UV range at wavelengths between 310 and 315 nm. The outcomes of this proposed method were then compared with those obtained using conventional industrial techniques for enhancing adhesion.

The investigation of the impact of spiral phase plates (SPP) aperture discretization on the orbital angular momentum (OAM) mode spectrum is presented in this work. It was shown that the position of the high-order unwanted modes in the OAM spectrum depends on the number of the angular sectors used for the SPP profile approximation. Thus, the performance of multi-OAM mode communication systems based on segmented SPP devices may suffer due to crosstalk between carrier and unwanted modes. The study was based on numerical and electromagnetic simulations of the OAM spectrum formed by segmented SPP operating in the millimeter wavelength range. The analytical expression for predicting the positions of unwanted modes in the OAM spectrum in order of descending mode purity (MP) values was formulated. This expression provides a quick and simple estimation of the OAM mode spectrum overlapping during the design of segmental SPP without simulations.

The design of a multilayer SIW cavity-fed filtenna is presented. The proposed filtenna can be used as a unified module in an antenna array structure. It consists of three-pole bandpass filter with slot antenna positioned centrally within the top module surface. The modules aperture dimensions of λ0/2×λ0/2 in conjunction with an SMA feeding port located on the bottom filtenna surface allow implementation of an antenna array of different configurations. This approach allows greatly simplifying the feeding and matching scheme of the array. This module is designed to operate at a 2.655 GHz central frequency with a 70 MHz bandwidth. The procedure of the filtenna design is described in detail. The proposed filtenna was fabricated and tested. The simulation and measurement results show a good agreement. The measurements demonstrate that the maximum measured gain of the prototype is 3.64 dBi with a small variation in the passband.

The use of waves carrying orbital angular momentum (OAM) is a promising way to extraordinarily increase the information capacity per communication channel due to their orthogonality. However, it is required the elaboration of devices and approaches for effective modulation/demodulation, multiplexing, and broadcasting of waves carrying several OAM modes The approach of binarization of the phase profile of the spiral phase plates based on pulse-width modulation (PWM) was presented and analyzed in this work. Based on numerical simulation, it was shown that PWM-like binary SPP allows forming waves carrying non-zero orbital angular momentum (OAM) modes of the same order $\vert l\vert$ and different signs simultaneously. The influence of the discretization parameter (NPWM) during PWM approximation of the phase profile on the OAM spectrum was considered.

We present a simple and efficient approach to calculate the effective dielectric constant of a composite material using equivalent circuit of its unit cell in this article. The equivalent capacitors model of a unit cell is used for the approximation of any number of inclusions of any shape using this method. The method's calculation process involves basic matrix operations to implement with different commercial or free software and programming languages. The comparison with other approaches as well as experimental results is presented, too.

This article presents a wide-angle-scanning leaky-wave antenna (LWA) based on a composite right/left-handed (CRLH) transmission line. In contrast to traditional semiconductor elements, thin-film ferroelectric capacitors were implemented in the CRLH unit cells to enable electric beam scanning. The proposed CRLH LWA has a single-layer design without metalized vias and is compatible with PCB and thin-film technologies. To fabricate the CRLH LWA prototype, dielectric material substrates and thin-film ferroelectric capacitors were manufactured, and their characteristics were investigated. Double-sided metalized fluoroplast-4 reinforced with fiberglass with a permittivity of 2.5 was used as a substrate for CRLH LWA prototyping. A solid solution of barium strontium titanate (BaxSr1−xTiO3) with a composition of x=0.3 was used as a ferroelectric material in electrically tunable capacitors. The characteristics of the manufactured ferroelectric thin-film capacitors were measured at a frequency of 1 GHz using the resonance method. The capacitors have a tunability of about two and a quality factor of about 50. The antenna prototype consists of ten units with a total length of 1.25 wavelengths at the operating frequency of close to 2.4 GHz. The experimental results demonstrate that the main beam can be shifted within the range of −40 to 16 degrees and has a gain of up to 3.2 dB. The simple design, low cost, and excellent wide-angle scanning make the proposed CRLH LWA viable in wireless communication systems.

Experimental results of vanadium dioxide film deposition on silicon carbide substrate are presented in this article. The study of the crystal structure and surface characteristics showed the high quality of the vanadium dioxide film.The obtained samples demonstrate a phase transition of more than 4 orders of magnitude and IR radiation modulation by 22.3%.

The split-cylinder resonator method was adapted to measure the microwave properties (dielectric permittivity and loss tangent) of thin ferroelectric films on a dielectric substrate. The mathematical model for calculating the resonance frequency of the split-cylinder resonator was adjusted for the “ferroelectric film—substrate” structure. An approach for correcting the gap effect based on calibrating with a single-layer dielectric was introduced and used to study two-layer dielectrics. The prototype of a split-cylinder resonator designed to measure single-layer dielectric plates at a frequency of 10 GHz was presented. The resonator calibration was performed using dielectric PTFE samples and fused silica, and an example of the correction function was suggested. The measurement error was estimated, and recommendations on the acceptable parameter range for the material under investigation were provided. The method was demonstrated to measure the microwave properties of a ferroelectric film on a fused silica substrate.

We developed a novel design of an electrically tunable wideband Fabry-Perot resonator antenna (FPRA). The antenna’s operating frequency band is 4.9–5.5 GHz, thereby it can be used in Wi-Fi terminals. To achieve a high gain value in the work frequency band, the tunable slot antenna loaded on thin film ferroelectric varactors was used as a feeding source. In the proposed antenna, varactors and control circuits were located on the bottom surface of the PCB plate in contrast to the existing designs. This minimized source antenna pattern distortion and increased total FPRA gain. Ferroelectric varactors were manufactured based on thin films of barium-strontium titanate in the paraelectric phase (with composition x=0.3). This material is attractive for use in microwave devices due to its high nonlinearity and low insertion losses. Ferroelectric varactors were produced, and their characteristics were measured. Obtained experimental data were used during the simulation of FPRA characteristics. Two-layer partially reflected surface was used to achieve a high gain value of the FPRA in the work frequency range. The simulation results showed that the proposed FPRA showed at least a 4 dB gain improvement in the frequency band of 4.9 to 5.5 GHz with a peak gain of 10.6 dB.

Introduction. The technology of printed circuit boards (PCBs) is widely used in modern electronic instrumentation. PCBs for the microwave frequency range are made based on foil composite materials, in particular, polytetrafluoroethylene (PTFE). At the moment, there is no domestic production of such a class of materials. Information concerning foreign manufacturing technologies in this field and the influence of the filler on the characteristics of the composite material remains confidential. Therefore, research into the properties of composite materials for microwave applications with properties similar to foreign analogues seems relevant.Aim. Experimental determination of the dependence of the electrical and mechanical properties of a composite material based on polytetrafluoroethylene depending on the concentration and size of the titanium dioxide fraction.Materials and methods. Experimental determination of the dependence of the electrical and mechanical properties of a composite material based on PTFE depending on the concentration and size of the titanium dioxide fraction.Results. The results of an experimental study of the mechanical properties and microwave parameters of experimental samples of composite material based on PTFE are presented, namely: composite material with 10 % content of ceramic titanium dioxide powders (fraction size 10, 49 and 126 µm); composite material with 5, 10 and 15 % content of ceramic titanium dioxide powder (fraction size 49 µm for polytetrafluoroethylene and 126 µm for titanium dioxide).Conclusion. The results obtained demonstrate prospects for using compositions based on PTFE and titanium dioxide powder as a basis for microwave materials. A correlation was established between the percentage of the introduced ceramic filler and the microwave parameters of the material. The studies demonstrated a slight difference in the microwave properties of the manufactured composite material samples with a different ratio between the particle sizes of titanium dioxide and PTFE. However, a significant decrease in their mechanical properties was observed.

In the present study, we investigated the use of a split-cylinder resonator and a slot line-based planar sensor for precise measurement. The dielectric wafer parameters had a thickness of millimeters and dielectric constants of ones to tens at a frequency of about 10 GHz. The resonant frequency, sensitivity, and inclusion coefficient were calculated for a split-cylinder resonator with a half-length L=16 mm and a radius a=20 mm for various thicknesses of dielectric wafers. The express monitoring method was based on a microstrip line coupled to a split-ring slot-line resonator formed in the ground. To avoid the measurement error caused by an uncontrolled air gap between the sensor and the sample, this air gap was introduced into the calculation model. The model was developed using conformal mapping and the partial capacitance method. The resonant frequency of the slotline resonator was estimated from the capacitances of the slotline-sample structure with and without a dielectric. The resonant frequency and sensitivity of the sensor were calculated depending on the dielectric constant of the sample and the gap widths of the slot.

The design of the CRLH unit cell with via-free topology was presented in this work. Such a topology allows simple integration of tunable elements. During simulation, results of measurements of ferroelectric tunable capacitors were used. For a substrate, the experimental material based on fluoroplast-4D (F4Dr) reinforced with fiberglass was considered. Full-wave simulation shows that 10 units cells leaky-wave antenna demonstrate gain ~5 dB with electrical beam scanning in range ~50 degrees in frequency range 2.35- 2.45 GHz.

A method is proposed for ion-plasma deposition of thin multicomponent films with the ability to control the component composition in thickness (graded film) with a change in the pressure of the working gas according to a given law. Using the Ba x Sr 1-x TiO 3 (BSTO)perovskite-type structure as an example, the calculated (Monte Carlo simulation) and experimental dependences of the component composition of films and their deposition rate on the pressure of the working gas were obtained. As an example, the possibility of deposition of BSTO films with a linear distribution of composition by their thickness. Keywords: ion-plasma deposition, thin multicomponent films, composition control.

Experimental results of the planar resistive element based on thin-film vanadium dioxide are presented in this article. Samples of thin films of vanadium dioxide with thickness 100 nm were obtained by magnetron sputtering. Triangular copper electrodes were formed on the film to provide a gap between vertexes of about $80\mu\mathrm{m}$. This gap is the place of the formation of the current-conducting channel during the phase transition. The change of the element resistance more than 3 orders was observed. Switching of the element occurred at 4 V across the gap at temperature stabilization at 322 K with the scale of the transient time of less than 1 ms.

Introduction. One of the directions in Fabry–Perot antenna design consists in increasing its operation frequency range. In the present work, we set out to develop a Fabry–Perot antenna with a smooth gain pattern across a wide frequency range. To that end, a tunable slot antenna based on a thin-film ferroelectric varactor was used. The major development criterion was a high uniformity of the gain pattern, not exceeding 1 dB in the given frequency band. Aim. To develop a Fabry–Perot antenna for the 4.9–5.5 GHz frequency range with a high gain uniformity within the operating frequency band. Materials and methods. The antenna under development was based on thin-film ferroelectric capacitors as tunable elements. Fluoroplastic plates metallized on both sides were used as a dielectric material for manufacturing a frequency selected surface and a slot antenna. The parameters of ferroelectric elements were measured using a resonance technique, while the parameters of the dielectric material were determined using the Nicholson–Ross–Weir method. Results. The developed antenna has an operating frequency band of 4.9–5.5 GHz. Samples of ferroelectric capacitors and foiled dielectric material were manufactured and experimentally investigated. A tunable slot antenna was fabricated, and its characteristics were measured. The simulation results show that the gain value of the developed Fabry–Perot antenna is not less than 10 dB in the operation frequency range. Variations in the gain value within the operating frequency band do not exceed 0.7 dB. Conclusion. A Fabry–Perot antenna based on an electrically tunable slot antenna and a two-layer frequency-selective surface was developed. The operating frequency band of the developed device ranges within 4.9–5.5 GHz, which corresponds to the frequency band of Wi-Fi networks. Optimization of the antenna design parameters made it possible to achieve higher gain values under their minor variations in the operation frequency band.

Introduction. In view of the ever-tightening bandwidth requirements for wireless communication systems, the use of tunable or switching devices based on microwave keys is becoming increasingly popular. Currently, the development of microwave keys based on nonlinear materials, such as vanadium dioxide, is a relevant research direction. The keys based on this material are distinguished by a planar and simple design, thus being suitable for creating microwave devices using hybrid technology.Aim. To study the properties of thin vanadium dioxide films and to develop a microwave switch with electrical switching on their basis.Materials and methods. Experimental samples of thin vanadium dioxide films were obtained by magnetron sputtering. The phase transition parameters of the samples obtained experimentally were used in computer simulation of a planar two-electrode structure of a microwave key by the finite element method.Results. Experimental samples of vanadium dioxide films were manufactured, and the dependences of their resistivity on temperature were studied. The resistance of the obtained vanadium dioxide films was found to change threefold. A microwave key design based on vanadium dioxide films was developed. The formation of a currentconducting channel in vanadium dioxide films was simulated when a control voltage was applied. The threshold voltage of the element was estimated depending on its design parameters.Conclusion. The use of experimental data as a basis for computer simulation made it possible to determine the threshold values of currents depending on the topology and design of the proposed microwave key. The results of simulating the key structure showed the formed conductive channel to have clearly defined boundaries in terms of distribution of both current density and temperature across the film surface.

The properties of spin-wave quanta, referred to as magnons, make them a promising signal carrier for the transmission and processing of information in magnetic materials. In this field, called magnonics, dynamic magnonic crystals attract special attention for applications such as complex real-time spectral transformations, due to on-demand controllability of transmission gaps. Here, we report on the experimental realization of the dynamic control of spin-wave band structures in artificial crystals using the metal-insulator transition in the vanadium dioxide (VO2) grating. The obtained results are confirmed by a theoretical approach predicting a dramatic variation of the reflection coefficient from the VO2 stripes upon the phase transition. The proposed structure combines the excellent versatility, fast switching speed, low power consumption, and external control it affords.