Introduction. Band-pass filters circuit elements can be calculated by converting low-pass filter (LPF) parameters, which is the prototype of the designed band-pass filter. The conversion causes problems in case calculated values of circuit elements (resistors and capacitors) are out of standard values determined by the GOST standard. Obviously, frequency characteristics of band-pass filters are distorted when replacing the calculated values of circuit elements by the standard ones. The number of circuit elements with values different from standard can be reduced to zero by solving an additional system of equations that connects parameters of designed and reintroduced non-equiripple frequency responses.
Objective. The objective of this work is to develop a calculation method of band-pass ladder filters with values of circuit elements corresponding to standard ones.
Materials and methods. The filter design process includes two stages. The first stage is a parameters calculation of a polynomial LPF prototype. The calculated parameters are determined as a system of equations solution set. The equations are formed by equating coefficients of variables raised to the same powers in transfer function (TF) expressions of designed and realized filters. Initial characteristics are the filter order and frequency response unevenness. The transition to the standard values of circuit elements can be done when solving another system of equations that connects LPF converted parameters with unknown parameters of reintroduced non-equiripple frequency response.
Results. TF of LPF prototypes up to the fifth order and frequency responses of band-pass filters (BPF) and bandrejection filters up to the tenth order are presented. Analytical expressions of non-equiripple and equiripple frequency responses are used to estimate distortions of the latter when a band-pass filter center frequency is tuned by using variable inductors or capacitors. The integral quadratic function of a variable is taken as a measure of real frequency response distortions. The tenth order BPF calculation example is given.
Conclusion. The presented calculation methods of band-pass filters and given example demonstrate possibilities of the filter design method based on the systems of non-linear equations solution. In contrast to approximation methods of ideal filter frequency response by using special functions and tabular filters design, the presented method allows high-order filter calculation for any initial requirements without using reference data.

Introduction. In order to automate data processing in remote observation systems using television and infrared cameras, synthetic aperture panoramic radars, as well as laser and acoustic systems, it is essential to be able to reliably detect, isolate, select and localise objects of various shapes in images.

Objective. The development of a methodology based on multi-threshold analysis.

Materials and methods. The developed image segmentation and object selection approach having optimal selection threshold assessment is based on the results of multi-threshold image analysis.

Results. Based on the analysis of a series of standard objects with known shapes hindered by synthetic noise, as well as representative examples of remotely sensed images of the Earth’s surface, improvements in the characteristics of both entire image segmentation and selection of particular objects according to several objective criteria were achieved.

Conclusion. The main advantage of the proposed approach consists in the minimisation of the post-processing shape modification of the selected objects. Although this is achieved at the cost of the resource-consuming multi-threshold analysis procedure for each processed image, this can be also partially compensated by the simplicity of the algorithm and its possible parallel implementation.

Introduction. Currently, one of the most promising approaches to the development of 5th generation mobile wireless systems is the deployment of heterogeneous networks based on existing LTE cellular systems having both large and small cells. Small, low-cost relay stations equipped with highly directional steerable antenna systems to connect small cells with LTE base station serving macrocell can comprise the main elements of such networks.

Objective. Since existing solutions are either too expensive or do not allow the flexible rearrangement of current information transmission lines, the objective of this work is to develop antenna equipment for low-cost relay stations based on simple, steerable antenna systems of millimetre wavelength (57-64 GHz), which allow beamsteering on both azimuth and elevation planes.

Methods and materials. The developed steerable, bifocal lens antenna system comprises a specially-shaped lens made of high-molecular-weight polyethylene and integrated with a phased array antenna. A key feature of its design is a wide-angle beamsteering in the azimuth plane and ability to adjust the beam in the elevation plane. The calculation of the lens profiles was carried out by means of an approximation of geometrical optics in Matlab, while the main technical characteristics of the lens antenna system were obtained by direct electromagnetic modelling in CST Microwave Studio.

Results. A prototype steerable, bifocal lens-array antenna system has been developed and its characteristics studied. The following technical characteristics are achieved in the 57–64 GHz range: beamsteering in the elevation plane – ±3º; beam-steering in the azimuth plane – ±40º; antenna gain – from 20 to 27.5 dBi for all angles.

Conclusion. It is shown that the developed antenna system can be successfully used as a component of the receiving and transmission equipment of small relay stations that transmit information in the frequency range of 57-64 GHz over a distance of 100-300 m.

Introduction. Millimeter-wave frequency range can provide utilization of wide transmission frequency bands and therefore a significant increase of the capacity in modern communication systems. One of the main concerns in the design of the 27.5…29.5 GHz-wave communication system is a high gain antenna of the range of 30 dBi to compensate the significant level of radio signal attenuation in the communication channel compared to the traditional frequency bands below 6 GHz.
Objective. Development of the integrated lens antenna with the ability to operate on two orthogonal linear polarizations to separate the transmitted and received signals by polarization and, therefore, to create more efficient use of the spectrum. At the same time, an important task is to provide a high aperture efficiency of the antenna and a low level of insertion loss in the distribution system, which should have an interface based on printed transmission lines for connection to the radio frequency circuit elements realized on the printed circuit board.
Materials and methods. The main method of the analysis of the lens antenna characteristics is full-wave electromagnetic simulation in the computer-aided design system CST Microwave Studio. The results are confirmed with experimental samples measurement.
Results. The designed antenna is an integrated lens antenna consisting of a homogeneous semi-elliptical dielectric lens with a diameter of D = 120 mm with a cylindrical extension and a primary radiator based on a microstrip antenna with a waveguide adapter. Waveguide adapter radiating opening dimensions were optimized using an analytical method based on a combination of geometrical and physical optics. Two orthogonal polarizations are excited on the primary microstrip patch antenna with the corresponding closely spaced “H-type” slots in one internal metallization layer. According to experimental results, the designed antenna provides the gain level of 29.5…30.2 dBi with a halfpower beamwidth of 4.8…5.1 degrees and cross-polarization level exceeding 37 dB for both polarizations in the whole frequency band of 27.5…29.5 GHz.
Conclusion. The simplicity of the design, high aperture efficiency and the ability to operate on two orthogonal linear polarizations show that the developed lens antenna can be successfully used in radio communication systems of the 27.5…29.5 GHz frequency range.

Introduction. Doppler spectra of signals which are scattered from sea surface and received by radar is used in oceanology and ecological monitoring applications. Existing models of Doppler spectra have the limitation of application because they are based on empirical data in changing conditions. Variability of the observation conditions critically influence on microwaves scattering by sea surface at low grazing angles which is typical for marine radiolocations.
Objective. The goal of investigation proposed in this article is to develop the mathematical model of Doppler spectra at low grazing angles for microwave frequency range.
Materials and methods. The two-dimensional problem of the scattering of an electromagnetic field on a cylindrical deterministic surface is considered. For generating of sea surface realizations is used linear model with spatial sea spectrum Elfohaily. The solution of the scattering problem is obtained for the case of vertical polarization of the incident electromagnetic field by the method of an integral equation with the control of the error of the solution. The mathematical modeling of the Doppler Spectrum of signal scattered by sea surface is produced by method of statistical trial. The case where the direction of the observation of the sea surface by radar is perpendicular to the direction of the wind is considered. The electromagnetic filed scattered in the direction of the radar receiver as a function of time is calculated for each generated sea surface realizations. Further, the set of variables of the implementation of scattered field is calculated for implementation of the Doppler spectrum.
Results. The set of implementations of the Doppler spectrum provided its mathematical model with consist of deterministic and random component. The approximation of each aforesaid component is suggested and mathematical expressions for value component calculation are presented. The analyze of modeling result is produced.
Conclusion. The developed mathematical model is offered to use for the design of algorithm sea surface condition estimation and pollutant detection using the signal which received by radar.

Introduction. The basis for solving the problem of aircraft recognition is the formation of radar portraits, reflecting the constructive features of aerial vehicles. Portraits, which are radar images of the propellers of aerial vehicles, have high informativeness. These images allow us to distinguish the number and relative position of the propeller blades, as well as the direction of its rotation. The basis for obtaining such images are mathematical models of reflected signals.
Objective. The aim of this paper is to develop mathematical models of the radar signal reflected from the helicopter main rotor applied to inverse synthetic aperture radar (ISAR).
Methods and materials. ISAR processing is used to produce a radar image of a propeller in a radar with a monochromatic probing signal. The propeller blades in the models are approximated by different geometric shapes. The models used to describe the reflection from the propellers of helicopters and fixed-wing aircraft have significant differences. In the process of moving each blade of the helicopter main rotor makes characteristic movements (flapping, dragging, feathering), as well as bends in a vertical plane. Such movements and bendings of the blades are influence the phase of the signal reflected from the main rotor. It is necessary to take the phase change of the reflected signal into account as accurately as possible when developing an ISAR algorithm for imaging the main rotor.
Results. We found that in the centimeter wavelength range the mathematical model of the signal reflected from the helicopter main rotor as a system of blades is most accurately described by representing each blade with a set of isotropic reflectors located on the main rotor’s blade leading and trailing edges. Taking into account the flapping movements and curved shapes of the blades in the model allows you to get as close as possible to the features of the real signal.
Conclusion. The developed model which takes into account the flapping movements and bends of the helicopter main rotor blades can be used to improve the ISAR algorithms providing the radar imaging of aerial vehicles.

Introduction. An incomplete list of graphene properties includes high electric conductivity, thermal conductivity, strength, large surface area, high light transmittance. Graphene is a very promising material from the point of view of its application in micro- and nanoelectronics. In addition, graphene advantage is a possibility of its obtaining by various ways. It allows creating materials with desired physicochemical properties by using appropriate technological methods.
Objective. The investigation of a thermal reduction temperature influence on physicochemical properties of graphene oxide (GO) films.
Materials and methods. In the present work, GO films are obtained on a slide surface by its immersing and removing from a graphene oxide water dispersion (dip coating). Obtained samples are studied by methods of scanning electron microscopy, Raman spectroscopy, and elemental CHN analysis. A sheet resistance is measured by a four-point probes method.
Results. A content difference of elements (C, H, N) in studied samples, and both graphene structure defectiveness and sheet resistance decrease, are found to be proportional to a reduction temperature increase. A GO films thickness decrease during a heat treatment is also observed, which is presumably associated with a functional GO groups loss while thermal reduction.
Conclusion. Research results demonstrate a possibility of a carbon films with desired physicochemical properties obtaining from a reduced graphene oxide (RGO), which can be used in thin-film technologies. Presented materials can also be useful in issues related to GO and RGO obtaining and applying.

Introduction. For a homodyne acousto-optic spectrum analyzer functioning a reference optical channel must be organized. The signal in this channel should provide uniform reference illumination throughout the spatial frequency range. In the general case, the spectrum analyzer functioning can be considered with a continuous photosensor and photosensor with charge accumulation. With the last one, the signal in the reference channel is proposed to be a wideband pulses periodic sequence.
Objective. Analyze the spectrum analyzer functioning with a periodic reference signal.
Materials and methods. We derive the mathematical expression to describe the influence of the reference signal structure on the analyzer’s output signal for the cases of continuous photosensor and photosensor with charge accumulation.
Results. It is shown that in the case of continuous photosensor, the reference signal periodicity does not lead to characteristics degradation. However, in the case of many frequency resolution points it is impractical, since each photodetector signal is parallel, processing is required: filtering, amplification and digitization. In the case of using of the charge accumulation sensor, the discrete frequency grid appears, which means signals omissions in frequency. This can be avoided by choosing the accumulation time equal to the minimum among the values of the acousto-optic modulator time aperture and the reference signal period, which is hard to implement, or still leads to the signal omissions in frequency or time.
Conclusion. To perform a real-time mode in the homodyne acousto-optic spectrum analyzer, the reference signal must be either non-periodic, which raises the question of its synthesis, or a continuous photodiode array should be used.

Introduction. X-ray methods are currently widely used in manufacturing of various products and components of the electronics industry, including micro- and nano-electronics. One of the most informative and illustrative methods is projection X-ray microscopy. Specialized X-ray systems for process control are developed and used in industry. The key element in the design of an X-ray inspection system is an X-ray tube. In the overwhelming majority of cases, X-ray inspection systems are based on collapsible microfocus x-ray tubes with constant pumping. This greatly complicates the design of the installation, increases its dimensions, weight and cost.
Objective. Analysis of possible technical and technological solutions that improve the availability of the X-ray system for monitoring of electronic components while maintaining the information content of the control.
Materials and methods. The article presents the results of analytical studies of assessment of the degree of influence of the main parameters of the X-ray tube – the size of the focal spot and the focal length – on the resolution of the resulting X-ray images. The advantages and disadvantages of two variants of the construction of the X-ray inspection systems are described: based on collapsible and based on sealed X-ray tubes. The dependence of the size of the focal spot on the voltage on the X-ray tube and on the power supplied by the electron beam to the target of the X-ray tube is analyzed. It is shown that sealed (from a vacuum pumping system) micro focus X-ray tubes can be successfully used as a radiation source in installations for X-ray inspection. It is concluded that in most cases, sealed tubes are more practical.
Results. In solving of most problems of non-destructive testing of electronic components in the composition of the Xray system, X-ray sources based on sealed X-ray tubes can be successfully used. Due to this, dimensions, weight, and the cost of an X-ray system for monitoring of electronic components are substantially reduced.
Conclusion. Sealed X-ray tubes are an effective alternative in the development of an X-ray system for monitoring of electronic components, which enables to fundamentally increase the availability of such a system.

Introduction. An assessing of the sportsman's physiological reserve (PR) and its dynamics is important when planning and carrying out a training, forecasting sportsman's results. An importance of this problem increases in highperformance sports, and energy consumption sports. A complexity of solving of this problem is caused by the requirement of taking into account of the complex of the biomedical parameters and formation of an integral parameter. This parameter reflects functioning of various body systems which provide significant income to the sportsman’s result achievement.
Objective. Development of the method and the system of PR assessing allowing complex investigation of the PR during the training process.
Method and materials. For achievement of the aim the tasks were formulated and solved using methods of biomedical research and engineering, mathematical processing and analysis of the diagnostically valuable parameters.
Results. The complex of the biomedical parameters reflecting sportsman’s body metabolism in condition of physical exercises is formed. They are the heart rate, the heart rate variability, the pulse frequency, the systolic and diastolic pressure, the respiratory rate, the blood saturation, and the stress index by Baevsky. It is important for PR assessing to assess parameters characterizing sportsman’s physiological reserves at the current moment and its dynamics. The circle diagram is proposed for taking into account of all mentioned parameters and its variation dynamics. The value of the integral PR parameter is an area of a polygon, which is obtained on the circle diagram using normalized values of the diagnostically significant parameters. The method of biomedical investigation of the sportsman and the method of PR assessing based on the complex of the body system parameters are developed. The scheme of assessing of sportsman's body physiological reserves before and after the training is proposed. The scheme allows to assess not only sportsman's body energy consumption during the training but also its recovery after the training. General structures of the biotechnical system and a structures of systems of picking up, registration, processing, and analysis of biomedical signals for assessing of sportsman's physiological reserves are developed. Special attention is given to the development of a wearable device for synchronous registration of the complex of biomedical parameters and algorithms of assessing of the diagnostically significant parameters of sportsman's body physiological reserves.
Conclusion. The proposed method of sportsman's physiologic reserves investigation and the structure of the system with spatially distributed architecture allow sport medicine doctor and coach to assess an efficiency of sportsman's training process with respect to his potential capabilities, and efficiently control the training process.

Introduction. Monitoring of the depth of anesthesia during surgery is a complex task. Since electroencephalogram (EEG) signals contain valuable information about processes in the brain, EEG analysis is considered to be one of the most useful methods for study and assessment of the depth of anesthesia in clinical applications. Anesthetics affect the frequency composition of the EEG. EEG of awake persons, as a rule, contains mixed alpha and beta rhythms. Changes in the EEG, caused by the transition from the waking state to the state of deep anesthesia, manifest as a shift of the spectral components of the signal to the lower part of the frequency range. Anesthetics cause a whole range of neurophysiological changes, which cannot be correctly assessed with just one indicator.
Objective. In order to describe complex processes during the transition from the waking state to the state of deep anesthesia adequately, it is required to propose a method for assessing the depth of anesthesia, using a comprehensive set of parameters reflecting changes in the EEG signal. The article presents the results of study the possibility of building a regression model based on artificial neural networks (ANN) to determine levels of anesthesia using a set of parameters calculated by EEG.
Materials and methods. The authors of the article propose the method for assessing the level of anesthesia, based on the use of neural networks, which input parameters are time and frequency EEG parameters, namely: spectral entropy (SE); burst-suppression ratio (BSR); spectral edge frequency (SEF95) and log power ratio of the spectrum (RBR) for three pairs of frequency ranges.
Results. The optimal parameters of ANN were determined, at which the highest level of regression is achieved between the calculated and the verified values of the anesthesia depth indices.
Conclusion. In order to create a practical version of the algorithm, it is necessary to investigate further the noise stability of the proposed method and develop a set of algorithmic solutions, which ensure a reliable operation of the algorithm in the presence of noise.