Introduction. Following an analysis of numerous literature sources, the article proposes a classification for GNSS interference mitigation methods and carries out an analytical review of these methods. The results of an analytical review of GNSS interference mitigation methods with signal processing in the time, frequency and time-frequency domains are presented.
Aim. To carry out a brief review of methods explaining the basic principles and approaches for suppressing GNSS interference based on signal processing in the time, frequency and time-frequency domains.
Materials and methods. The analysis of the considered methods was based on the materials of literature sources published in 2000–2024 (mostly in English). The literature search was conducted based on the following criteria: firstly, the application of mitigation methods specifically to GNSS interference, and secondly, those with the theoretical justification and experimental confirmation of the effectiveness of the proposed methods. This article discusses methods for GNSS interference mitigation based on signal processing in the time, frequency and time-frequency domains using adaptive notch filters, spectral analysis, Short-Time Fourier Transform (STFT), Wigner–Ville Distribution (WVD), and its modifications.
Results. A classification for GNSS interference mitigation methods is proposed. On this basis, a comparative analysis of anti-interference methods and algorithms using signal processing in one-dimensional and two-dimensional domains (time, frequency and time-frequency) is carried out.
Conclusion. The conducted review and comparative analysis of the most common and effective methods of GNSS interference mitigation is intended to assist researchers and developers in reducing the time required to study the diversity of approaches to solving this problem proposed in the current literature. The next article on this topic will consider methods for GNSS interference mitigation using the Wavelet Transformmethod, as well as signal processing in the spatial and space-time domains.

Introduction. The ever-increasing demands on the speed of information transmission lead to an increasing adoption of MIMO systems in telecommunication networks. There are a number of works devoted to the possibility of using MIMO antenna modules based on SIW resonators. One of the promising directions in this field is the use of 1/4 and 1/8 mode SIW resonators, which can significantly reduce the weight and size characteristics of the device. The main disadvantages of such MIMO antennas are the narrow frequency band and a relatively low isolation of the radiators. Therefore, the advancement of engineering approaches to designing MIMO modules that boost these attributes is a relevant research task.
Aim. Development of innovative engineering approaches to designing antenna modules utilizing 1/8 mode SIW resonators for application in MIMO, which enhance their radiation properties and improve the isolation between the radiators.
Materials and methods. The characteristics of the antenna module were simulated in software packages using the finite element method. The prototype antenna module was manufactured using a metallized composite polytetrafluoroethylene material. The network analyzer Ceyear 3272C was used to measure the characteristics of the antenna module prototype.
Results. The MIMO module based on two 1/8-mode SAW resonators with notable improvement in both the gain of the radiation elements and their isolation was developed. The results of a study into the relationship between substrate thickness and the features of the module are presented. The possibility of using the developed module in dual-band systems by operating not only on the main, but also on the higher resonant mode of SIW resonators is demonstrated. The design of a MIMO module consisting of eight radiation elements is proposed.
Conclusion. The MIMO module design based on two 1/8-mode SIW resonators separated by a gap can be used in dual-band systems operated in several modes. An increase in the substrate thickness was shown to lead to both an improvement in the module’s antenna gain and a reduction in their insulation effectiveness. An antenna module design based on a pair of 1/8-mode SAW resonators, which enables improved insulation between the radiators (up to –30 dB), is proposed.

Introduction. In connection with the active development of satellite systems using low-orbit, medium-orbit and highly elliptical spacecraft, an important task is to ensure continuous reception-transmission of signals by antenna systems for both mobile and stationary ground-based communication terminals. As a rule, scanning antenna systems are used in ground terminals of such systems. Nowadays, antenna systems with mechanoelectric scanning have been developed due to the fact that such systems achieve high directivity in a wide range of angles while maintaining small dimensions of the antenna and its low cost. One of the possible elements of beam control are waveguide phase shifters due to their simple realization, low losses and low cost.
Aim. Development of a mechanoelectric scanning antenna array capable of providing beam tunability within ±60°.
Materials and methods. Numerical investigations have been carried out by finite element method in time domain.
Results. A broadband microstrip radiating element operating in the frequency range of 10.7…14.5 GHz has been developed and a scanning antenna array has been constructed on its basis. The control element of the array is a proposed phase shifter on a gap-waveguide, which provides phase adjustment of more than 360°. According to the results of electrodynamic modeling, the antenna array demonstrated the possibility of scanning within ±60° with a degradation of the directivity factor less than 3 dB over the entire operating frequency range.
Conclusion. This paper considers the development of a mechanoelectric scanning antenna system with a mechanical phase shifter as a beam steering element. The developed antenna array allows to provide scanning in the sector of angles ±60°.

Introduction. The operation of a radar system of automatic range tracking (ATR), equipped with a moving target selector (MTS) for the purpose of increasing assessment accuracy, under conditions of intensive passive interference in the form of reflections from the Earth's surface is considered. The level of such passive interference can significantly exceed useful signals. Range tracking by the ATR system is carried out by a pair of tracking half-strobes, which receive weakly correlated signals from different parts of the Earth's surface during each probing of the space. This reduces the efficiency of the MTS system and increases the error of range measurement.
Aim. To study the correlation properties of passive interference in the modes of search and automatic tracking of moving targets by the ATR system depending on probing pulse duration and target velocity. To determine the efficiency of the MTS system as part of the ATR system when exposed to correlated interference. To evaluate the effect of probing pulse duration and target velocity on the passive interference suppression coefficient and range discriminator operation when the ATR system operates in the search and automatic tracking modes.
Materials and methods. The method of correlation analysis of statistical properties of signals and devices for their processing was used.
Results. We derived an expression for the correlation function of signal fluctuations reflected by a homogeneous Earth's surface, taking into account probing pulse duration and target velocity as applied to pulse Doppler radars. The results of calculating the passive interference suppression coefficient by means of the MTS as part of an interference-proof range discriminator for various values of probing pulse duration and target velocity are presented. It is shown that a decrease in probing pulse duration, as well as an increase in target velocity, leads to a significant decrease in the passive interference suppression coefficient and an increase in the dispersion of the interference signal at the output of the range discriminator of the ATR system. Thus, when the target velocity interval is τ = 0.2 s, the target velocity is νp = 500 km/h, and the probing pulse duration varies from 1 to 0.1 μs, the correlation coefficient of the inter-period fluctuations of the passive interference r_м (nT ) decreases from 0.83 to 0.67, resulting in a decrease in the suppression coefficient of the passive interference by the MTS system.

Conclusion. The results obtained can be used when designing pulse Doppler radars using interference-proof systems for measuring the parameters of moving targets.

Introduction. Complex signals are widely used in radar location. The use of phased array antennas (PAA) offers additional opportunities for covert operation of radar systems by increasing their noise immunity and electromagnetic compatibility. This article compares the energy concealment of a radar system with a multi-frequency probing signal with spatial frequency modulation and that of an analogous system without additional spatial modulation.
Aim. Analysis of the energy concealment of radar operation with spatial frequency modulation of a quasicontinuous multi-frequency probing signal in a transmitting-and-receiving PAA. Materials and methods. The signal security and mutual influence was analyzed using an energy receiver (ER) with an input filter and an amplitude detector. The characteristics of signal security were obtained using a set of ambiguity functions (AF) in the temporal, frequency, and spatial domains. Signals with continuous and quasi-continuous radiation were considered.
Results. Estimates of the gain in the signal level received at the ER input at different angles of its location relative to the target are obtained. The analysis is performed when the signal spectrum matches the ER filter band. A situation with the known angular position of the ER is considered. An algorithm for adaptive formation of the PAA pattern with zero radiation in the direction of the ER is proposed. In this case, interference side lobes of a multi-dimensional spatiotemporal AF may occur, for which an inconsistent correlation processing algorithm is considered. Estimates of the loss in terms of signal/noise due to misalignment are given. The energy concealment of a radar system with spatial modulation and a conventional radar with a similar multi-frequency probing signal in terms of energy and the number of bands and an identical equidistant N-element FAA, but without additional spatial modulation, is carried out.
Conclusion. The results obtained indicate the possibility of increasing the communication security of radar operation due to additional spatial modulation of the multi-frequency probing signal. In this case, energy losses associated with the use of multi-channel spatial-frequency correlation processing are absent.

Introduction. In order to solve a number of problems arising in the process of airspace control, it is necessary to determine the class (type) of the objects observed. In addition, differentiation between targets located in the same element of the spatial resolution of a radar system is highly relevant. Construction of radar images of aircraft blades based on the method of inverse synthetic aperture radar (ISAR) can become an efficient tool in solving this problem. The development of resolution algorithms using the ISAR method requires a sufficiently accurate model of the reflected signal that would take into account the design features of the aircraft rotor blade. The available mathematical models for the signal reflected from the rotating blades of an aircraft are, as a rule, over-simplified, thus inhibiting the implementation of an adequate ISAR-based algorithm.
Aim. Refinement of a mathematical model of the signal reflected from the quadcopter rotor blade based on experimental studies in application to the ISAR method.
Materials and methods. The rotor blade in the considered model is represented by a set of point reflectors located on the approximating segments of the front and rear edges of the blade. When developing a reflected signal model, changes in the phase structure of the reflected signal are taken into account due to the translational motion of the quadcopter and the rotation of the propeller blades, as well as the spread of the blades in space.
Results. A mathematical model of the signal reflected from the quadcopter rotor blade was obtained, which demonstrates good convergence with reality. By means of modeling, the implementations of signals reflected from one quadcopter blade are obtained. The temporal and spectral structures of the reflected signals obtained as a result of modeling and experimental studies are compared.
Conclusion. The refined mathematical model of the reflected signal, which takes into account the design features of the quadcopter blade, can serve as a basis for developing an algorithm for imaging quadcopter blades using the method of ISAR.

Introduction. Currently in gas sensing there is an urgent need to improve performance, including sensor response and speed, as well as to reduce operating temperatures. To achieve these goals, multicomponent oxide systems are being studied. Various modifications of Zn–Sn–O system are among the most promising materials.
Aim. To develop techniques for the hydrothermal preparation of zinc hydroxostannate nanoparticles using different precursors. Active layers for gas sensors were created and tested using these synthesized nanoparticles.
Materials and methods. Zinc hydroxostannate nanoparticles were synthesized using hydrothermal methods for 6 hours at a temperature of 90 °C. Two techniques using different precursors were used to obtain the samples. The samples were then analyzed using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Based on the optical spectroscopy results, the band gap of zinc hydroxostannate was determined. Gas sensing properties of the nanoparticles were investigated under different conditions, including target gases, temperatures, and exposure to UV radiation.
Results. A comprehensive study of the synthesized structures has shown that the nature of their interaction with target gases is different depending on the synthesis technique. Specifically, ZnSn(OH)6_1 samples demonstrate a response at room temperature and are highly rapid. This is attributed to the predominance of zinc ions on their surface. In contrast, ZnSn(OH)6_2 samples, with a surface rich in tin ions surrounded by OH groups, require additional activation by UV radiation to achieve a response at room temperature. At the same time, the response and recovery times are in the order of hundreds of seconds.
Conclusion. The paper explores the potential of using zinc hydroxostannate nanoparticles created through the hydrothermal process for room temperature gas sensors. The key factor in this study is the selection of the synthesis technique.

Introduction. Ferrite non-reciprocal devices are widely used in various space qualified transmit/receive modules. The layout of modern satellite communication systems is becoming more compact, which requires multifunctional devices capable of replacing several different components. Thus, the creation of hybrid ferrite devices capable of performing additional functions along with microwave signal isolation represents a relevant research task.
Aim. Creation of a multifunctional hybrid device for high RF power. Development of a telemetry sensor capable of providing a DC voltage value proportional to the level of reflected power.
Materials and methods. Calculations were performed in specialized CAD systems for electrodynamic and thermal analysis. Measurements and tests on high RF power were performed using the facilities of the Ferrite-Domen Scientific Research Institute.
Results. A multifunctional ferrite device with a built-in reflected power telemetry sensor is developed. The sensor is implemented exclusively on passive components; the hybrid device does not require an external power source. The DC voltage value at the sensor output does not exceed 4.5 V. The required dependence of the output voltage on the reflected power value is obtained. The device exhibits increased reliability, meeting the requirements of modern space application systems. Its input/output VSWR does not exceed 1.25, with the insertion and isolation losses being no more than 0.35 dB and no less than 20 dB, respectively.
Conclusion. The developed multifunctional device meets modern requirements for space electronic components. The implemented reflected power sensor has no analogues in the world. The obtained results can serve as a basis for the creation of similar devices for different frequencies and power levels

Introduction. Bandwidth broadening and the growing complexity of the signal waveform result in the inadequacy of modern behavioral models used for simulating baseband devices (before and after the demodulator). To measure devices with an overshoot at the flat top of the transient response (TR), a nonlinear dynamic model in the form of a secondorder recursive filter can be used, whose characteristics are currently determined by the variational method. This article presents an alternative approach to measuring the characteristics of baseband devices with an overshoot at the flat top of TR. In this approach, the processing of results does not involve variational algorithms; instead, it qualifies as an indirect measurement of the characteristic functions of a second-order nonlinear recursive filter.
Aim. To consider an approach to determining the characteristics of nonlinear dynamical baseband devices with an overshoot at the flat top of the TR using non-iterative calculations based on the results of direct measurements.
Materials and methods. A device with an overshoot at the flat top on the TR is simulated by an equivalent electrical circuit, consisting of an in-series connected inductor and resistor with a parallel connected capacitor. The task is to determine the characteristics of each component: the voltage-current characteristic (VCC), the charge-voltage characteristic (CVC), and the magnetic flux-current characteristic (MFCC). The measurement object was a National Instruments PXI-5114 oscilloscope.
Results. The developed measurement technique has made it possible to accurately determine VCC, CVC, and MFCC for a device with an overshoot at the flat top without the need for iterative calculations (using indirect measurements). The error in the simulated TR using these measurements in relation to the actual values did not exceed 9 %, which is an acceptable result.
Conclusion. The proposed method for calculating characteristic functions without the need for iterations allows for the independent determination of the nonlinear characteristics of devices with an overshoot at the flat top of TR by setting the strobing point at various moments in time. The method is promising for further applications.