Introduction. The mitigation of interferences that degrade the performance of navigation systems constitutes one of the most significant problems of contemporary satellite navigation. This problem is conventionally solved using digital adaptive space filters. Depending on a particular radio technical system, the mathematical description of digital signal processing methods may involve specific calculation structures implemented using specific calculation algorithms. For example, the use of centrosymmetric linear and circular antenna arrays in a radio navigation system allows the description of such systems in terms of Toeplitz and circulant sample covariance matrices, respectively, and the inversion of such matrices by means of special numerical methods in order to design a digital filter.

Aim. A comparative analysis of the performance of space signal processing algorithms is carried out along with an estimation of Toeplitz and circulant sample covariance matrices and numerical methods of their inversion. The previously obtained results in this field are clarified.

Materials and methods. An analysis of algorithm performance was carried out in the MATLAB environment using experimental recordings of satellite navigation signals and jammers obtained by an actual radio technical system.

Results. A new expression was derived for estimating circulant sample covariance matrices. Formulae that describe a modification of the Bareiss numerical Toeplitz matrix inversion algorithm for the case of complex Hermitian matrix were introduced. An analysis of the results of computer simulation allowed the algorithms with the highest performance to be indicated. The amount of time taken by the algorithms based on Toeplitz and circulant matrices did not exceed 2.5 10⋅ ⁻³ s and 0.04 s, respectively. The carrier-to-noise ratio in the processed signal was at least 46 dB. 

Conclusion. The formulae obtained and the algorithms analyzed can be used when implementing adaptive digital filtering of satellite navigation signals.

Introduction. Phased antenna arrays (PAA) of large geometric dimensions find wide application in various spacecraft systems. The PAA design assumes the deployment of its sections in outer space to form a plane of the radiating aperture. However, when implementing such a design, locally flat violations of the radiating aperture may occur. In turn, this may lead to distortion of the original amplitude and phase distribution (APD) under the correct antenna deployment. As a result, the shape of the radiation pattern (RP) changes, in particular, its main maximum shifts and the level of side lobes increases. Under these conditions, in order to ensure the formation of a pattern with the given parameters, it is necessary to correct the APD in a PAA.

Aim. To develop a method for correcting the APD in a PAA under the known parameters of violations in the radiating aperture geometry.

Materials and methods. The method is based on the condition of minimizing the root-mean-square deviation of the RP formed after correction from the original RP in the absence of aperture violations. The basis of the method is the formation of a redefined system of linear algebraic equations (SLAE) connecting the parameters of geometry violations with RP distortions. Each of the SLAE equations corresponds to a certain angular direction in space, in which the condition of coincidence of the original and corrected RP is imposed.

Results. A method for correcting the APD in the presence of locally flat violations of the PAA radiating aperture is proposed. Numerical simulation of the relationship between the parameters of violations and the directional characteristics was carried out. The main relations and results of numerical simulation are presented, in particular, the amplitude distributions, as well as the cross sections of the formed RP and the difference of the normalized RP in the presence of errors in the deployment of the PAA web both without and with APD correction.

Conclusion. The results obtained show that, in the absence of APD correction in the PAA aperture, the formation of RP with the given parameters cannot be ensured. In particular, there is a shift of the main maximum of the RP and a change in the nature of the envelope of the side lobes. At the same time, APD correction makes it possible to maintain the RP practically unchanged.

Introduction. Approaches to the introduction of negative feedback in pulse control systems regulating the parameters of electricity flow with pulse-width modulation (PWM) continue to attract research attention in the field of switch power amplifiers (SPA) and switch voltage converters (SVC). Evaluation of the potential of compensation methods is of importance when selecting power electronics devices for various purposes.

Aim. To review compensation methods for parameter regulation and to investigate conditions for the operational stability of SVC with feedback on output voltage and current.

Materials and methods. The research methodology included the theory of pulsed automatic control systems, the method of harmonic linearization with stability assessment according to Nyquist criteria, and the generating filter method based on multiple frequencies.

Results. An analysis of operational stability conditions was carried out.  Analytical dependences and graphical representation of the limit feedback values from the modulation parameters and the switch transformation scheme were proposed.

Conclusion. The conducted study of the feedback depth in SVC, limited by the penetration of high-frequency components into the path of a width-modulated signal and its delay, due to the peculiarities of the terminal stage of the SPA, demonstrates that the limit value of the voltage feedback depth at typical circuit parameters does not exceed 12 dB, while the depth of the current feedback of the filter choke of the low frequencies can be fundamentally (more than 20 dB) higher. At the same time, the implementation of voltage stabilization and output current limitation modes for maintaining reliable operation in start-up and overload modes is possible only with the use of combined feedback.

Introduction. The quality of input information for trajectory processing (TP) systems can be improved by increasing the measurement accuracy of radar sensors (RS). However, in such a case, radar targets acquire the characteristics of complex targets having several marks at the output of the detector. This makes it difficult to accurately assess the kinetic parameters of targets in a TP system. In this respect, the development of a generalized algorithm for processing and generating data from the reflected signals of complex targets seems a relevant research task.

Aim. To investigate reasons for the formation of complex targets and, using the theory of radar image processing, to synthesize an algorithm for processing and generating data on reflected signals from a complex target.

Materials and methods. The following methodological approaches were used: the theory of digital signal processing; applied theory of radar image processing; MATLAB Simulink Toolboxes for simulating radar image processing; some prerequisites for fuzzy clustering methods.

Results. Following an analysis of some characteristics of complex targets and the theory of radar image processing, an generalized algorithm was synthesized for processing and generating data of reflected signals from this class of targets. The results can be used to improve the measurement accuracy of their representative point when solving the TP problem.

Conclusion. Reasons for the formation of complex targets in radar technology were analyzed. Their specific features consist in the need to accurately assess a true mark. A generalized algorithm for processing and generating these signals reflected from complex targets was proposed. The results can serve as a basis for solving the TP problem.

Introduction. Designers of modern on-board systems for communication, radar, and radio monitoring face the problem of improving their qualitative characteristics, including the operating frequency, instantaneous bandwidth, receiver sensitivity, and electromagnetic compatibility. In addition, the dimensions, weight, and power of such systems, as well their cost, should be minimized. However, the current semiconductor microwave electronics has reached its limits in terms of frequency and dynamic characteristics. A possible solution consists in the implementation of microwave photonic transmission lines in the design of on-board systems for communication, radar, and radio monitoring on the basis of modulation of laser radiation by means of electro-absorption.

Aim. To study the transfer characteristics and noise figure of a microwave photonic transmission line realized based on the modulation of laser radiation by means of electro-absorption. To compare the results of theoretical calculations and experimental investigations.

Materials and methods. The research methodology involved external modulation using an electro-absorption modulator (EAM), mathematical representation of the transmission coefficient, as well as comparison of the theoretical and practical results.

Results. Theoretical values of the transmission coefficient and noise figure for a microwave photonic transmission line based on the external modulation method using an EAM were obtained. Experimental values of the transmission coefficient and noise figure for a microwave photonic line in the frequency range from 100 MHz to 16 GHz were presented. The obtained data were compared with those of the nearest mass-produced products of foreign production and those presented in domestic publications on microwave photonic signal transmission lines.

Conclusion. The use of an EAM, whose main advantage consists in the possibility of integration with a laser emitter, allowed the authors to design and manufacture a small-sized industrial prototype of a radio-photonic transceiver, capable of transmitting a radio signal over tens of kilometers in the frequency range from 100 MHz to 12 GHz with a transmission coefficient of at least −3 dB and a noise figure no more than 36 dB at the upper operating frequency. At the same time, the closest analogue manufactured by Emcore with similar dimensions has a transmission coefficient of −30 dB and uses direct modulation of laser radiation as a transmission method, which significantly reduces the transmission range of the microwave signal.

Introduction. Recently, the development of tunable microwave photonic filters has attracted great scientific and practical interest. Such microwave photonic filters are a good alternative to traditional electrical solutions, due to low losses, wide operating frequency range and such filters can be easily integrated into various telecommunication systems. By using an acetylene reference cell and a laser with tunable wavelength can make it possible to create tunable microwave photonic filter with wide operating frequency range.

Aim. Investigation of the characteristic of a tunable microwave photonic filter based on an acetylene reference cell, as well as research possible solution to reduce losses in filter bandwidth; numerical simulation of microwave photonic filter characteristics.

Materials and methods. Experimental study was carried out on an experimental prototype of a tunable microwave photonic filter. The filter consisted of a laser with a tunable wavelength, a phase modulator, an acetylene reference cell, an optical fiber connecting the gas cell with a photodetector, and a photodetector. Theoretical study was carried out by modeling of the transmission characteristics of the microwave photonic filter.

Results. Experimental transmission characteristics of a tunable microwave photonic filter were obtained. The tuning of the filter bandwidth by tuning laser wavelength was studied. Modeling of transmission characteristics of microwave photonic filter was performed. Possible solution to reduce losses in filter bandwidth was proposed.

Conclusion. A tunable microwave photonic filter based on an acetylene reference cell is proposed. Losses in the filter bandwidth was about −30 dB. Using high-power laser and a photodetector with a high photocurrent can reduce losses in the filter bandwidth.

Introduction. Acoustic profiling is a conventional method for studying the geological structure of the seabed. To this end, a low-frequency acoustic profiler with an operating frequency range of 1…14 kHz can be used. However, under lower operating frequencies, the difficulty of achieving the required resolution arises. The problem of improving the angular resolution of a hydroacoustic device, particularly in the direction of the carrier movement, remains to be a priority task in the search and detection of objects on the seabed, as well as the study of the bottom soil structure. Angular resolution can be improved through several approaches, including an algorithm for synthesizing the antenna aperture based on the law of the phase change of the reflected signal. This approach is relevant in the design of highresolution hydroacoustic tools.

Aim. To demonstrate the possibility of constructing a bottom soil profiling device, as well as the possibility of increasing its angular resolution based on an algorithm for synthesizing the antenna aperture of an acoustic profiler.

Materials and methods. The study employed the groundwork data obtained for side-scan sonars with a synthetic aperture in terms of constructing an antenna device and the methods of radio-wave excitation developed for radar systems.

Results. The possibility of synthesizing the antenna aperture for an acoustic profiler of the bottom soil was studied. An algorithm for synthesizing the antenna aperture was investigated along with phase distortions of the trajectory signal and their influence on the sonar image. The fundamental principles of processing the trajectory signal were considered.

Conclusion. An approach to increasing the resolution of an acoustic profiler when performing search and survey tasks is proposed. The proposed design of the acoustic part of a profiling device can be used in the development of search and survey hydroacoustic devices with a high angular resolution.

Introduction. Reducing the duration of the probing pulse at the output of a multilayer radiator is an urgent task of acoustic non-destructive testing. This not only improves the resolution of the system and the accuracy of determining the coordinates of defects, but also reduces the length of the dead zone. The most versatile method for achieving short signal duration is mechanical damping. The use of RL circuits connected to the electrical side of a piezoelectric transducer (PET) for this purpose has been studied to a lesser extent. Of interest is a comparative study of the potential possibilities of the two indicated methods for obtaining a short signal.

Aim. To carry out a comparative study of two options for reducing the duration of the probing signal in order to establish their preferential use in the practice of ultrasonic testing.

Materials and methods. To determine the boundaries of the preferred application of one of the methods in comparison with the other, a mathematical apparatus is used based on the use of integral calculus, as well as numerical calculation methods. When constructing a mathematical model of piezoelectric transducers operating in a pulsed mode, the method of analog circuits is used in combination with the spectral method based on Fourier transforms. Numerical calculations were performed in the MathCad environment.

Results. It was established that the use of an electrical corrective circuit with optimal parameters makes it possible, across a wide range of changes in the values of the specific acoustic resistance of the protector, to achieve a shorter duration of probing signals at the output of the probe than in the case of using a damped probe with values of the specific acoustic resistance of the damper z_д latitude 10⋅10⁶ Pa⋅s/m. At z_д >10⋅10⁶ Pa⋅s/m, preference should be given to mechanical damping of the piezoelectric element. It was found that the amplitude of the signals at the output of the PET with a corrective circuit connected thereto exceeds the amplitude of the signal when the piezoelectric element is damped.

Conclusion. The results obtained allow an a-priori evaluation and comparison of PET capabilities using two methods for creating a short probing signal, as well as a justified selection of materials for creating a protector across a wide range of specific acoustic resistances. The correctly selected parameters of the structural elements of the probe makes it possible to improve the resolution of radiation-reception systems, reduce the length of the dead zone, and increase the accuracy of determining the coordinates of defects. This ultimately improves the quality of acoustic testing of materials and products.

Introduction. Measurements of the amplitude-time characteristics of pulsed magnetic fields are required in various research and technology areas. Such measurements are carried out during pulsed magnetic field immunity testing, with the magnetic field pulse rise time being hundreds of ns, and the pulse duration to its half initial value (halfdroop) being hundreds of µs.

Aim. To develop a meter of magnetic field strength with a linear conversion characteristic for measuring the pulse rise time, the pulse duration to its half-droop, and the peak value of the pulsed magnetic field strength.

Materials and methods. Among several available methods for measuring pulsed magnetic field parameters, the induction method was selected. To obtain a signal proportional to the pulsed magnetic field strength, a signal from the induction transducer is integrated using a self-integrating induction transducer (RL integration) or by using an external RC integrator. The former method shows good results when measuring signals with a duration of hundreds of ns; however, this method is inefficient when measuring the parameters of longer-duration pulses. The latter method is used to determine the parameters of signals with a duration of hundreds of µs and ms; however, this method gives a large error when measuring the parameters of signals with a duration of hundreds of ns and less. The consecutive use of the two integration methods leads to an additional error in the measurement of the pulse duration to its half-drop.

Results. A setup for determining the required magnetic field pulse parameters using a pulse magnetic field meter based on an RL integrator was developed. The relative measurement errors comprised 10, 10, and 9 %, respectively. The developed setup eliminates the error caused by losses in the active resistance of an induction transducer, thus enabling the pulse duration to its half-droop to be measured without additional errors under the pulse rise time of hundreds of ns and the pulse droop time of hundreds of µs.

Conclusion. The development of a functional converter made it possible to extend the frequency response of a pulsed magnetic field meter based on an RL integrator to the low-frequency region.