Introduction. Enhancing the resolution of radar stations beyond the Rayleigh limit is particularly important for modern radio electronic systems operating under conditions of low signal-to-noise ratios and intense external interference. This task becomes crucial for ensuring accurate detection and identification of objects at significant distances, which extend possibilities for applying this technology. Inverse filtering (IF) is an effective processing method; however, in standard cases, its efficiency depends significantly on the noise environment, limiting its application in real-world scenarios.

Aim. Development and investigation of an approach aimed at enhancing IF efficiency by introducing a basis correction method, which improves signal processing quality and increases system robustness to interference.

Materials and methods. The research was carried out using the methods of mathematical simulation of filtering processes and analysis of the influence of various parameters on the IF efficiency. Simulation studies were conducted in a specially developed software environment. The methods of signal processing theory, including matrix theory and probability theory, were used.

Results. A method of basis correction is proposed, which increases the efficiency of IF by increasing the signal-tonoise ratio at the filter output. Dependencies of the signal-to-noise ratio on correction parameters are obtained. The concept of the mean square of the filter's impulse response norm is introduced, providing an additional analytical tool for evaluating and optimizing the method. A practical approach for implementing the method to enhance the resolution of radar systems is proposed.

Conclusion. The basis correction method improves the efficiency of IF and extends its application capabilities in the conditions of a low input signal-to-noise ratio. The research significance consists in the development of a novel methodology for improving signal processing quality in radar systems, which extends their applicability under adverse signal reception conditions.

Introduction. Shifts in the habitat ranges of tree species are among the continental-scale consequences of climate change. Mapping these shifts and their quantitative estimation are essential for evaluating the carbon balance. In this work, a method for mapping long-term changes in forest cover, thus permitting evaluation of treeline shifts, is demonstrated on the example of the mountain ecosystem of the Subpolar Urals. The stages of preliminary selection and processing of Landsat multispectral remote sensing data from the Google Earth Engine platform are described. The results of mapping long-term changes in forest cover and quantitative estimation of the total area of treeline transition are presented.

Aim. Mapping of long-term changes in forest cover and their quantitative estimation using Landsat multispectral remote sensing data and expert assessments of ecological zone boundaries in the mountains of the Subpolar Urals (on the example of the Sablya Ridge).

Materials and methods. Cloud-free multispectral images from Landsat satellites 4–9 of top-of-atmosphere reflectance, which underwent relative radiometric correction, as well as surface reflectance data, were used. Expert assessments of ecological zone boundaries were obtained, and regression analysis was used.

Results. Based on the statistical time series analysis for the period from 1987 to 2024, the total area of treeline transition from 1960 to 2024 was established to be 4.82 km². An acceleration of treeline transition from 1970 to 1995 was recorded.

Conclusion. The described method allows long-term spatial dynamics of treeline shifts to be mapped and quantitatively estimated. The obtained estimates agree well with those obtained by expert assessment. The recorded period of accelerated treeline transition coincides with that of global temperature changes.

Introduction. The angular method of locating overlapping spectrum radio sources (RS) is supplemented by spatial filtering (SPF) of their multipath signals. The cross-correlation function (CCF) between the estimates of signals at the reception point (RP) allows extraction of RS signals with a minimum delay corresponding to the true position of RS under a certain configuration of the multi-position receiving system. The CCF between the estimates of signals in different points allows matching the position lines defined by the estimates of azimuth and elevation angle corresponding to the same RS thus avoiding the formation of false points and areas of location.

Aim. Development and investigation of a method for matching position lines based on RS signal estimates obtained by spatial filtering in different receiving points.

Materials and methods. The MUSIC method was used to estimate the direction of arrival of overlapping spectrum signals in different RPs. Based on these estimates, the coefficients of the spatial filter for RS signal selection were calculated using the least squares criterion. Calculating the CCF estimates of signals at a fixed RP eliminates the reflected signals from further analysis. The quality of SPF is improved with an inaccurately specified amplitude–phase distribution (APD) of the antenna array (AA) by rejecting non-suppressed interfering signals. The study was carried out by statistical simulation in the MATLAB environment.

Results. Under an accurate APD definition of the AA the probability of locating RS with signals of any intensity reaches 100 %. The worst results are achieved when one strong RS signal dominates in all reception points under inaccurate definition of the APD of AA. In such a case, the application of additional rejection increases the probability of correct location of weak RS from 40 to 90 %.

Conclusion. Depending on different propagation conditions and signal levels, the accuracy of _АА calibration and the probability of location of weak signal sources exceeds 90 %.

Introduction. The most common helicopters are those based on a single rotor design, each with a main rotor and a tail rotor. Radar images of helicopter rotors, combined with their rotational speeds, contain information that allows the helicopter type to be determined. The amplitude modulation law for signals reflected from the main rotor blades is of a pulse nature. These modulation pulses significantly exceed the amplitude of the signal reflected from the airframe. Therefore, constructing an image of the main rotor presents no fundamental difficulties. However, the amplitudes of signals reflected from the tail rotor blades are significantly smaller than those of the main rotor. Therefore, the problem of measuring the rotational speed of the tail rotor blades against the background signal of the tail rotor is not solved. Consequently, the problem of constructing an image of the tail rotor is not solved. This problem is additionally complicated by the overlapping spectra of the signals reflected from the main and tail rotors.

Aim. Development of a method for compensating the helicopter rotor signal in the time domain.

Materials and methods. Compensation for signals reflected from main rotor blades can be accomplished through various approaches. This paper discusses a method based on the use of complex amplitude moduli of reference signals in the main rotor imaging channel. These moduli are used to generate a time-domain weighting function for signals reflected from the main rotor blades. This function, by weighting the received signal, ensures compensation for reflections from the main rotor blades.

Results. A method for compensating for the helicopter main rotor signal in the time domain has been developed for constructing a radar image of the helicopter tail rotor. The method does not require extensive computational resources. Its effectiveness is illustrated using a signal reflected from an Mi-8 helicopter as an example.

Conclusion. The developed method enables compensation for signals reflected from the blades of the helicopter main rotor and creates conditions for measuring the rotation frequency and constructing an image of the helicopter tail rotor. 

Introduction. The current advancement of 4H-SiC-based power electronics is driven by rapid progress in bulk and epitaxial growth technology of silicon carbide (SiC) crystals. This determines the demand for improved designs and manufacturing technologies of MOS transistors (MOSFET) and Schottky diodes. Research in this field is highly relevant for a widespread implementation of SiC devices in various areas of power electronics and conversion technology for achieving the required levels of energy efficiency.

Aim. Research and comparative analysis of electrical characteristics of 4H-SiC power MOSFET laboratory samples with linear and hexagonal base cell designs.

Materials and methods. The initial objects of the study were laboratory samples of 4H-SiC-MOSFET with two types of cells and a small-size active area, designed for voltages up to 1200 V. At a later stage, 4H-SiC-MOSFET laboratory samples with optimized parameters of a linear-type cell and a larger active area were manufactured and investigated. The transistors were manufactured via a laboratory technological route without applying a self-aligned channel technology. The samples were characterized using optical and scanning electron microscopy (SEM). Electrical parameters were measured by a Keysight B1505A curve tracer.

Results. The comparative analysis of the output characteristics of the samples showed that transistors with a hexagonal cell topology outperform those with a linear topology in terms of higher values of switching currents. However, the maximum current density J_DS = 125 A/cm² is not critical for silicon carbide. Improved transistors with a linear topology with reduced channel dimensions and an increased active area are characterized by a higher current density and a lower channel resistance in the open state (Ron).

Conclusion. Transistor samples with a hexagonal cell topology in comparison with those with a linear topology, under equal R_on, demonstrate higher values of switched currents but lower reproducibility of parameters. Laboratory samples with an improved linear cell topology are characterized by ~ 4 times lower R_on compared to those with a small active area. Nevertheless, the achieved transistor yield in terms of threshold voltage U_th was less than 10 %, which indicates the necessity of implementation of self-aligned channel technologies and high-resolution lithography in their manufacturing route when scaling up their production.

Introduction. Passive spectral remote sensing techniques have come a long way to become the main source of information on the Earth’s surface and atmosphere. Multispectral and hyperspectral cameras are now produced on a mass scale; however, their wider use is still impeded by high cost. Commercially available affordable complementary metal–oxide semiconductor (CMOS) image sensors provide a suitable basis for the development of low-cost multispectral cameras.

Aim. To design and test a portable multispectral camera intended for environmental monitoring in the field.

Materials and methods. The camera design is based on a single CMOS image sensor. Spectral bands are selected by interchangeable interference filters installed in two gear wheels. The optical system of the camera forms a parallel beam of light before its passing through a filter followed by focusing in the sensor plane. Filter switching is performed by a stepping motor. Its rotation, as well as image acquisition and storage, is controlled by a Raspberry Pi single-board computer. Multispectral images were processed using scripts in the Python language.

Results. The optical design of the newly created camera was tested to assess the size and spectral uniformity of its field of view. In addition, the camera was used to obtain several images of vegetation cover. Further, spatial distributions of two vegetation indices – the normalized difference vegetation index (NDVI) and the green–red vegetation index (GRVI) – were calculated. These distributions allowed areas occupied by vegetation to be successfully detected and coniferous trees to be separated from deciduous ones.

Conclusion. The results obtained have confirmed the feasibility of the proposed optical and mechanical design for remote assessment of the ecological status of vegetation cover.

Introduction. Ka-band power amplifier MMICs are essential components of many electronic systems. Their application area covers radar, 5G communication, and test equipment. The design of a reliable power amplifier with high-performance characteristics is a challenging task.

Aim. Design of two types millimeter-wave wideband power amplifier (PA) MMICs by using 0.13 µm GaAs pseudomorphic high-electron mobility transistor (pHEMT) technology process.

Materials and methods. A cell unit measuring 8 × _{50 μ}m was used in the design of both amplifiers. The first PA MMIC included three stages, with the overall gate periphery of the third stage being 0.8 mm. The second PA MMIC was realized as a parallel combining of the first PA structure, using Wilkinson combiners. The two types of MMICs were fabricated through 0.13 _μm GaAs pHEMT technology, realized at the Istok NPP. RF testing was carried out both on wafer and in assembly to measure S parameters and power characteristics under CW test conditions and different ambient temperature.

Results. The first PA MMIC demonstrates a saturated output power of more than 25.5 dBm with an associated PAE above 19 % in the 26…38 GHz frequency band. The saturated output power of the second PA MMIC exceeds 28.4 dBm with more than 19 % PAE over the 26…38 GHz band. The circuits show a gain of 17.5 and 17 dB for the first and second PA MMICs, respectively.

Conclusion. Two types of millimeter-wave wideband PA MMICs were fabricated using 0.13 _μm GaAs pHEMT technology. The designed PA MMICs represent devices with a wideband small-signal and power performance, which makes them suitable for wideband wireless communication, radar, and test equipment applications.

Introduction. In modern industrial production, the role of information and measurement systems for monitoring and diagnostics at all stages of the technological process cannot be underestimated. The increasing complexity of objects leads to a growing volume of measurement information, which reduces the promptness and reliability of monitoring and diagnostics. The conventional approach consists in increasing the computational power, which only postpones the problem. As an alternative, this article proposes changes in the existing algorithmic support by introducing an adaptability mechanism. Adaptive commutation in multichannel technical diagnostic systems with time-division channeling enhances the reliability of monitoring and diagnosing the object under study.

Aim. To develop an algorithmic support for multichannel technical diagnostic systems and, on this basis, to propose a possible version of the structural diagram.

Materials and methods. The study of the adaptation mechanism for multichannel technical diagnostic systems was conducted using the methods of statistical modeling borrowed from queuing theory, with the diagnostic system itself represented as a queuing system.

Results. An algorithmic support and a structural diagram for a multichannel adaptive technical diagnostics system are developed. Mathematical calculations were performed to estimate the multichannel-induced error for this type of systems. The research results can be applied when developing various types of information and measurement systems.

Conclusion. The application of adaptive priority polling in multichannel technical diagnostic systems enhances the reliability and speed of locating faults in complex engineering objects. The studied mathematical framework for assessing the methodological error associated with multichannel operation allows its permissible error margins to be accurately determined.

Introduction. When the optical system of a spacecraft rotates, the motion of its internal components initiates the emergence of a reactive torque. This torque causes unintended angular displacement of the spacecraft body, leading to a deviation of the line of sight and the formation of images with geometric distortions, commonly referred to as spatial blur. Such distortions limit the quality of remote sensing and astrophotography data. Despite the extensive study of stabilization problems, the influence of internal reactive torque arising from the motion of internal optical elements on the spatial accuracy of line-of-sight stabilization remains insufficiently investigated.

Aim. To evaluate the effect of the reactive torque of an opt_оmechanical system on the spatial blur of the resultant image and to determine whether the blur level complies with the acceptable requirements for data quality.

Materials and methods. An analysis of angular oscillations of an actual spacecraft during the operation of its optomechanical system was conducted based on the data of gyroscopic measurements. To estimate the amount of image blur, time series of angular velocities were processed at intervals corresponding to the camera exposure time. On this basis, the shift of the line-of-sight axis and the linear shift of the image in the focal plane were calculated. Additionally, a mathematical model based on the methods of theoretical mechanics was used to describe the relationship between the reactive torque of the rotating optical system and the dynamic response of the spacecraft body. This model made it possible to compare the actual data obtained with the calculated effect of the reactive torque.

Results. The analysis established the presence of low-frequency angular oscillations, creating a spatial blur of several micrometers. In this case, the modulation transfer function remains above 0.99, indicating minimal impact on image quality. The developed model confirmed the dependence of the angular deflection amplitude on the magnitude of the reactive torque.

Conclusion. The reactive torque of an optomechanical system with a value of less than 0.05 N·m cause image blur; however, its magnitude is insignificant. Thus, the MTF of 0.99 corresponds to maintaining the required clarity.