Introduction. An important task faced by the developers of modern telecommunication systems consists in increasing the noise immunity of signal reception in channels with variable parameters. Thus, the communication lines of DVB-T2, DVB-S, and DVB-S2/S2 standards widely apply signal structures (SS) of multi-position quadrature amplitude modulation (M-QAM). However, an analysis of scientific publications shows that the random nature of the phase change of the transformed signal constellation leads to a loss of noise immunity of the M-QAM signals. Engineering solutions for the effective reception of such signals are lacking. The proposed block diagram of a device for receiving quadrature amplitude signals and the developed operation algorithm for an amplitude-phase detector allow random phase changes to be considered and reduced.

Aim. Development of scientific and engineering proposals to improve the efficiency of receiving M-QAM signals in radio channels with random phase changes.

Materials and methods. The study was conducted using the methods of noise immunity research, as well as communication theory and signal theory.

Results. A block diagram of a device for receiving quadrature amplitude signals and an operation algorithm for an amplitude-phase detector were proposed, which allow random phase changes to be considered and compensated for. Scientific and engineering proposals were formulated to improve the noise immunity of M-QAM reception in channels with variable parameters.

Conclusion. The developed scientific and engineering proposals for increasing the noise immunity of multi-position quadrature signals in channels with variable parameters substantiate both the feasibility of using a transformed SS M-QAM with improved energy characteristics, as well as the application of the developed receiving device for processing quadrature amplitude signals and the operation algorithm of an amplitude-phase detector. The results obtained make it possible to perform demodulation with simultaneous compensation of phase distortions to increase the noise immunity of M-QAM signal reception.

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. Spatial filtering of signals is performed for the selection the signals of interest when the signals spectra overlap. The quality of spatial filtering depends on the accuracy of antenna array (AA) calibration, which allows estimation of the amplitude-phase distribution (APD) at all possible directions of arrival, thus ensuring the identity of reception paths. A mismatch between the actual and measured APD values leads to quality degradation in all spatial filtering methods.

Aim. To develop a method for improving the quality of signal spatial filtering based on the estimates of the desired and interfering signal arrival directions formed by the MUSIC and ESPRIT algorithms under a priori uncertainty and imprecise AA calibration.

Materials and methods. The quality of spatial filtering is improved by rejecting the interfering signals unsuppressed due to imprecisely measured APD of an AA. Statistical simulation modeling was carried out in the MATLAB environment; the data obtained experimentally were analyzed.

Results. A method for spatial filtering based on MUSIC and ESPRIT completed with an additional rejection of unsuppressed interfering signals due to imprecise AA calibration is developed. An algorithm for basis construction for rejection under of a priori uncertainty of the signal-interference environment is substantiated. The results of statistical simulation modeling and experimental data processing have shown the feasibility of additional rejection applied to the selected signals by spatial filtering.

Conclusion. The developed method for spatial filtering under the conditions of a priori uncertainty of the signal-interference situation and imprecise calibration of AA and reception paths ensures high quality characteristics across a wide dynamic range of desired and interfering signals. Whereas the Capon's method, which requires a priori knowledge of the arrival direction of the desired signal or its estimation, is capable of selecting only weak signals and suppressing strong ones under the conditions of imprecise APD.

Introduction. The distinction of targets located in the same spatial resolution cell of a radar system includes the determination of the number of targets and their recognition. Recognition and distinction are directly related to the analysis of radar profiles (spectral, range, azimuth, etc.). Radar images of rotating drone elements obtained with the method of inverse synthetic aperture radar (ISAR) present particular interest. Such profiles are highly informative in terms of defining the drone design characteristics. When developing algorithms for constructing radar profiles of drone propellers based on ISAR, it is necessary to have a clear understanding of the movements of various points on the propeller blade surfaces. This understanding can be achieved by constructing a mathematical model for a signal reflected from drone propellers.

Aim. To develop a mathematical model for a signal reflected from drone propellers in application to the method of ISAR in bistatic radar.

Materials and methods. In the model under consideration, the propeller blade is represented by a set of point reflectors located along two lines passing through the front and rear edges of the blade. When developing the reflected signal model, variation in the phase structure of the reflected signal arising due to the translational motion of the drone and the rotation of its propeller blades, as well as their offset in space.

Results. A mathematical model for a signal reflected from drone propellers in application to the method of ISAR in bistatic radar was developed. Signals reflected from one propeller blade, from one propeller, and from a set of drone propellers were simulated. The temporal and spectral structures of the reflected signals for two variants of blade representation were analyzed.

Conclusion. The developed mathematical model can be used when developing an algorithm for constructing images of drone propellers by the method of inverse synthetic aperture radar in a bistatic radar system.

Introduction. Recent years have seen a growing interest in studying the nonlinear properties of spin waves. Nonlinear phenomena, such as envelope solitons, nonlinear frequency shifts of intense spin waves, and etc., have attracted particular attention. However, a number of important issues remain to be underexplored, including the problem of induced nonlinear phase shift of spin waves. The relevance of this problem is related to the need to develop spin-wave logic gates that could be controlled by changing the spin wave phase.

Aim. To study a nonlinear XNOR logic gate whose operation is based on the induced nonlinear phase shift of a spin wave.

Materials and methods. An original theory is used to simulate the frequency response of a nonlinear XNOR logic gate. The operating principle of the nonlinear XNOR logic gate is substantiated. The possibility of implementing the nonlinear XNOR logic gate in a circuit similar to a spin-wave Mach-Zehnder interferometer is experimentally demonstrated.

Results. An experimental study of the induced nonlinear phase shift of operating signals incident on identical nonlinear spin-wave phase shifters located in the arms of the logic gate was carried out. It is shown that an increase in the pump signal power up to 60 mW, supplied to nonlinear phase shifters, changes the induced nonlinear phase shift of the operating signal by more than 180°. Hence, nonlinear phase shifters can be used for constructing spin-wave logic gates. In addition, the operating principle of a spin-wave logic gate was experimentally studied. It is shown that the XNOR logical function is implemented in the low-frequency part of the device’s frequency response characteristic.

Conclusion. Numerical simulation of the characteristics of a nonlinear XNOR logic gate based on the Mach-Zehnder interferometer circuit was carried out. It is shown that its logical functions are implemented due to the effect of an induced nonlinear phase shift of spin waves in nonlinear phase shifters located in different arms of the logic gate.

Introduction. Determination of the electrophysical parameters of linear and nonlinear dielectric materials for use in microwave technology represents an important direction. Linear dielectrics are used as a basis for the substrates of microwave circuits, as well as volumetric elements for the construction of frequency selective or resonant structures that operate across a wide temperature range. Therefore, the issue of stabilizing the electrical parameters of such structures from temperature influences appears relevant. A possible solution lies in the use of a multilayer combination of dielectrics, both with linear and nonlinear properties. Due to their nonlinear properties, ferroelectrics find application in functional units with an electrical rearrangement of frequency and phase characteristics. Therefore, it is important to determine not only the relative permittivity of the material, but also the control coefficient in the RF– microwave wavelength ranges.

Aim. Construction of computational mathematical models for layered bulk and film structures to determine the relative permittivity of linear and nonlinear dielectrics in the ultrahigh frequency range.

Materials and methods. The construction of computational mathematical models for the analysis of complex layered structures was carried out on the basis of Maxwell’s equations and the Galerkin method using boundary conditions for electromagnetic field components.

Results. An electrodynamic analysis of a two-layer volumetric disk resonator was performed, and numerical results of calculating the resonant frequency were obtained. A numerical analysis of a multielectrode half-wave resonator with a ferroelectric film (FEF) was carried out.

Conclusion. The mathematical models created and the experiment performed made it possible to numerically evaluate the properties of linear and nonlinear dielectric bulk and film materials in the microwave range.

Introduction. Non-Foster elements (NFEs) mimic behavior of hypothetical negative inductors or capacitors in a certain frequency band. NFEs are used to compensate reactance of conventional inductors and capacitors that allows designing broadband microwave devices. To realize NFEs, active circuits referred to as negative impedance converters (NICs) are employed to convert the load impedance into the negative input impedance. The conversion error, caused by non-optimal choice of NIC parameters and non-idealities of NIC components, limits the accuracy and operating bandwidth of NFEs. The necessity to account for many factors, which indirectly and oppositely impact the final result, and unavailability of a universal design methodology complicate the design of NFEs significantly. As a result, broadband NFE characteristics differ from the target ones remarkably that limits practical applications.

Aim. Elaboration of a design methodology to compensate the Linvill’s NIC conversion error and realize high-accuracy broadband negative inductors.

Materials and methods. Influence of NIC constituent parameters on the negative inductor frequency characteristics is considered. The performed analysis and the identified relationships allowed us to propose a step-by-step methodology to design negative inductors having tight tolerance over a broad frequency band. The use of a transmission line section instead of a lumped inductor in the NIC load when realizing negative inductors of high absolute values is shown to be advantageous as this allows providing better tolerance and wider bandwidth.

Results. In order to demonstrate possibilities enabled by the proposed methodology, simulation results are presented for the GHz-range negative inductors with a set of inductance and tolerance values.

Conclusion. The results obtained show that the proposed methodology makes it possible to compensate the conversion error without any numerical optimization and therefore to reduce the deviation of the negative inductance from the target value in the given frequency range or to broaden the bandwidth for a given tolerable deviation of the negative inductance.

Introduction. The development of new structural materials and improvement of existing technologies for the production of new products on their basis lead to the emergence of new types of medium discontinuities. Therefore, the development of new models of discontinuities that take the previously ignored parameters into account seems to be relevant for the purposes of nondestructive testing and structural measurements. This concerns, e.g., the roughness of adjacent surfaces of microcrack ordered sets.

Aim. Theoretical substantiation for the processes of elastic waves propagation through an elastic medium containing an ordered lattice of microcracks with boundary conditions in the linear slip approximation, modified by taking into account the parameters of micro-convexities of microcrack rough boundaries. Database formation for experimental studies aimed at determining the physical and mechanical characteristics of structural materials.

Materials and methods. The acoustic characteristics of materials were determined based on the derivation and solutions of dispersion equations describing the formation and propagation of effective longitudinal, transverse, and Rayleigh surface elastic waves in elastic media with ordered cracking. Their values were also used to determine the effective speed of Rayleigh surface waves.

Results. The conducted simulation of elastic wave formation processes showed that an increase in the concentration of microcracks leads to a decrease in the phase velocities of effective longitudinal, transverse, and surface waves, as well as to an increase in the attenuation coefficients at given ultrasound frequencies and material parameters.

Conclusion. The radius of the microsphere that replaces the surface micro-convexity and the roughness parameter R_z have a significant impact on the formation of physical and mechanical characteristics of materials, which are determined by the results of ultrasonic measurements. The developed model can be recommended as a basis for interpreting the results of ultrasonic measurements.

Introduction. Analysis of the quality of wheat grain using instrumental methods is an important task due to the permanent growth in annual wheat production and export. Digital radiography is a promising method for studying the internal structure of wheat grain. Along with other methods, digital radiography allows non-destructive testing and comprehensive description of grain parameters.

Aim. To determine the capabilities of digital radiography for studying the structure of wheat grain.

Materials and methods. Digital X-ray images were obtained using a multifunctional mobile x-ray diagnostic unit produced by JSC "ELTECH-Med" was used with the installation tube voltage of 9 kV. Durum wheat grain samples of different varieties were used. Operations for processing grain images were automated using the scripts developed in Python using the numpy and opencv libraries.

Results. The attenuation of X-ray radiation by grain material was studied. Wheat bran was found to exhibit a greater attenuation coefficient than the endosperm, assumably due to the higher concentration of potassium and phosphorus in the wheat outer layer. The calculated ratio of the attenuation coefficients of the bran to the endosperm was 1.27, compared to the experimentally obtained value of 1.36. The influence of the geometric shape of wheat grain on the formation of its X-ray image was determined. A method for describing the geometric shape of wheat grain using second-order curves was presented. A mathematical model for the transmission of X-ray radiation in wheat grain was constructed, taking into account its complex shape and the heterogeneous distribution of macroelements therein. This model allows estimation of the attenuation coefficients of the grain endosperm and outer layer using a non-destructive method.

Conclusion. Digital radiography is an effective method for studying wheat when carrying out research and breeding tasks. The proposed model for the transmission of X-ray radiation in wheat grain can be used to numerically determine some indicators of grain quality.