Introduction. Safety issues of railway transport are inevitably connected with the condition of railway tracks and railway wheels. Various defects, such as irregularities of the railway track, may lead to emergencies and incidents. Therefore, it is important to measure and calculate short and impulse irregularities. A joint analysis of vibration acceleration signals is needed in order to study the types and size of railway track irregularities.

Aim. Development of an algorithm for irregularity search based on accelerometer readings with the vertical measurement axis.

Materials and methods. The research encompassed wavelet transformation and wavelet-based signal processing including discrete-time signal processing and continuous wavelet processing. In addition, time-frequency analysis based on Fourier transform and continuous wavelet scalogram was used. These methods provide for time-frequency localization for irregularity detection and measurement.

Results. Algorithms for vibrational signal processing using the continuous and discrete-time wavelet transform are proposed. The results show that the discrete wavelet transform is effective for multiresolution and multiband analysis, and continuous wavelet transform and wavelet scalogram allows extraction of irregularities and determination of their parameters. The relative error for irregularity depth was improved by 18 %, and the absolute error for irregularity length determinations was reduced by 7 times.

Conclusion. Application of the discrete Fourier transform and Fourier spectrogram provides for fine resolution in the frequency domain. However, separation of signal components in the time-frequency domain is impeded. The continuous-time wavelet transform ensures sufficient resolution in the low-frequency domain for component localization and visualization of irregularities.

Introduction. Bandpass filters on surface acoustic waves (SAW) are important components in frequency selection devices for receiving and transmitting electronic equipment. Among the variety of existing requirements for SAW filters, particular attention is paid to those for the quality of characteristics, including reduction of insertion losses, unevenness in the bandwidth, etc., and those for reducing the development time of the filter. Reduction in the development time along with a simultaneous reduction in expenses can be achieved through the application of preliminary computer simulation. This task can be implemented only through an integrated approach to developing a computer-aided design system capable of solving optimization problems with a large number of degrees of freedom.

Aim. Development of a prototype of a fully functional complex for simulating and calculating SAW filters. Approbation of work on the creation of actual frequency filters on the example of resonator SAW filters with low losses on leaky SAWs. Development of a methodological approach to creation of a technology of computer-aided design of SAW filters using optimization algorithms.

Materials and methods. The theoretical part of the work was carried out using statistical analysis methods, circuit theory, and coupled mode theory. In the course of the work, mathematical processing and calculation were carried out in the MATLAB environment.

Results. A concept for creating a system of automated design of SAW filters with specified frequency characteristics was developed. An original method is proposed for optimizing the topology of SAW filter elements to obtain the maximum achievable frequency responses. The proposed approach was tested when calculating a resonator filter on leaky SAWs at 64° YX-cut lithium niobate.

Conclusion. The proposed integrated approach to designing SAW filters allows a rapid and relatively accurate prediction of filter characteristics at the modeling stage, which has a significant advantage compared to conducting numerous real experimental studies or numerical studies in the presence of a large number of degrees of freedom.

Introduction. Modern radio engineering systems impose strict requirements on the stability of the frequency of microwave oscillation sources (microwave generators) included in their composition. However, microwave oscillators (on dielectric resonators or resonators on surface acoustic waves), despite the low levels of power spectral density of frequency fluctuations of the generated signals, fail to exhibit the frequency stability required for most precision applications (phase noise meters, aircraft radars, ultra-low-noise frequency synthesizers). It is possible to increase the frequency stability of such oscillators, e.g., by using of a phase-locked loop system; however, for its implementation, as a rule, an electronic frequency tuning unit should be included in the microwave oscillator. The introduction of such a unit into the microwave oscillator can lead to degradation of its other electrical characteristics, e.g., the power spectral density of frequency fluctuations of the generated signals.

Aim. Development of a method for synthesizing electronic frequency tuning blocks with the required range of introduced phase shift and minimal intrinsic power loss for narrow-band microwave oscillators with resonators based on surface acoustic waves.

Materials and methods. The synthesis of electronic frequency tuning blocks is carried out by a numerical-analytical method using the MATLAB (academic license no. 906991) environment. The obtained results are analyzed by a comparative method.

Results. The paper presents a methodology for synthesizing electronic frequency tuning blocks with the required range of changes in the introduced phase shift while maintaining minimal insertion losses, which makes it possible to consider the intrinsic parasitic parameters of the varactor. Recommendations on the correct choice of varactors are given. A comparative analysis of calculated and practical results is carried out. The electronic frequency tuning unit was implemented on the basis of "Radiocomp" in 2023.

Conclusion. The presented methodology for synthesizing electronic frequency tuning blocks is versatile and can be used not only for the synthesis of electronic frequency tuning blocks of various narrow-band microwave oscillators using twoport resonators as a frequency-setting element, but also for the synthesis of narrow-band microwave phase shifters. 

Introduction. The conventional approach to extending the operating frequency band of Vivaldi antenna arrays consists in increasing the radiating element length. However, this inevitably leads to an increase in the mass of the entire array, and, therefore, to a rapid growth in the cross-polarization level. Recent studies in this field have mainly focused on techniques for reducing the cross-polarization level. At the same time, the possibility of developing Vivaldi antenna arrays with an extended operating frequency band, primarily without changing the overall dimensions of the elements or the antenna array pitch, remains insufficiently studied.

Aim. Design and study of the Vivaldi antenna radiating element that ensures operation of the array in a wider operating frequency band without increasing its overall dimensions and weight.

Materials and methods. A numerical study of the characteristics of a unit-cell with periodic boundary conditions on the side faces was carried out in the ANSYS HFSS software. A comparative analysis of the unit-cell characteristics of the prototype antenna array and the proposed design was carried out.

Results. The design of the Vivaldi antenna radiating element is presented. The influence of some geometric parameters on the characteristics of the antenna array is studied. A comparative analysis of the unit-cell characteristics of two infinite single-polarization antenna arrays based on a regular Vivaldi element and the proposed solution is carried out. The possibility of improving the antenna array bandwidth by 18.6 % and improving cross-polarization by 15 dB on certain frequencies without increasing the overall dimensions or the antenna array pitch is shown.

Conclusion. The proposed Vivaldi antenna design makes it possible to extend its operating frequency band without increasing the overall dimensions. The results of the conducted numerical study should be used when developing antenna arrays based on the proposed solution.

Introduction. Currently, the impact of phase shifter (PS) failures on the characteristics of phased antenna arrays, slotted waveguide array antenna (SWAA) in particular, represents a significant problem. A review of publications shows that insufficient attention has been paid to PS failures.

Aim. To investigate the characteristics of a SWAA in the event of PS failures, when their phase takes a value equal to zero instead of the required value.

Materials and methods. The methods of statistical modeling methods were used to study the impact of failures on SWA characteristics. Calculations were carried using the Mathcad 15 software package.

Results. An algorithm for statistical modeling of the impact of PS failures on SWAA characteristics is proposed. A relationship that connects the radiation pattern with the volume of the statistical sample and the number of failed PSs is given. The malfunctions of emitters from 5 to 35 out of 50 elements were studied. Changes in the following characteristics were obtained: standard deviation – from 0.064 to 0.18, radiation pattern width – from 8 to 18 %, the level of side lobes – from 13 to 59 %, radiation power – from 0.9 to 0.3.

Conclusion. The results obtained can be used in radio-electronic systems with antenna arrays at the stage of their development. Future work will address PS failures with phases being established randomly and with random values, as well as the case of PS failures where power does not pass into the emitter. Another important direction concerns compensation of distortions resulting from failures of antenna elements.

Introduction. Passive radars perform target detection based on reflected signals emitted by third-party transmitters. The absence of its own transmitter determines the main advantages of passive radars compared to conventional active radars: lower cost, silent operation, no electromagnetic impact on other radio equipment and the environment. Third-party transmitters of different telecommunication systems are currently used as illuminators of opportunity in passive radars. The emergence of new telecommunication standards opens additional prospects for the development of passive radars. For instance, the deployment of the fifth generation of mobile communications standard 5G with a higher bandwidth can potentially improve the accuracy of target detection in passive radars. Investigating the possibility of using signals from 5G transmitters for radar targets illumination is a relevant research task.

Aim. To analyze the possibilities, limitations and prospects of using 5G signals as illuminators of opportunity in passive radar systems.

Materials and methods. The methods of passive radar theory, communication theory, and comparative analysis were used. Evaluation of potential characteristics of target detection was carried out using computer statistical modelling in the MATLAB environment.

Results. The peculiarities of 5G signals from the point of view of their application as illumination signals in passive radars are investigated. The potential target detection characteristics of a passive radar using 5G signals for target illumination are evaluated and compared with those of passive radars operating on signals from other transmitters. The 5G signal provides an improved range and velocity resolution than signals from other telecommunication systems.

Conclusion. The comparative analysis shows that 5G NR signal transmitters can be used as a promising source of illumination in passive radar systems over relatively small areas.

Introduction. Modern mobile control objects require the use of highly sensitive transducers of motion parameters, e.g., acceleration, with a wide measurement range. Increased sensitivity to measured parameters can be achieved by using precision optics, e.g., based on the tunneling effect. However, operating ranges of induced movements are less than a micrometer, which creates difficulties in positioning the sensing element. In order to improve manufacturability, to extend the measurement range and to reduce errors of acceleration transducers with optical tunneling, compensation circuits with a piezoelectric actuator as an active sensor can be used.

Aim. To extend the measurement range of microelectromechanical acceleration transducers through the use of an integrated approach, including the introduction of a compensation circuit for sensor movements based on the inverse piezoelectric effect and detection of these movements by optical means.

Materials and methods. An approach to compensating sensor movements is proposed. This approach consists in using a bimorph piezoelectric plate as an inertial element. The use of optical reading of sensor sub-micrometer displacements is considered.

Results. A block scheme and a functional scheme of a compensator micro-opto-electromechanical acceleration transducer with a bimorph piezoelectric sensing element are developed. Deformations in the sensing element under the influence of accelerations (up to 100 m/s²) and compensation voltages, whose amplitude does not exceed several volts, are investigated to ensure the possibility of using the optical tunneling effect in the proposed transducer.

Conclusion. A mathematical model of the transducer was developed and studied. A 2.5-fold increase in the  measurement range was achieved. It was shown that the introduction of compensation feedback does not decrease the permissible frequency range of measured accelerations.

Introduction. Directional drilling is a conventional method for trenchless installation of underground communications, exploration of solid minerals, and geological exploration. These tasks can be implemented using a directional drilling installation equipped with a high-precision unit for determining the drilling head coordinates to match the current and specified drilling routes. The problem of obtaining precise coordinates (depth, zenith, azimuth) of the drilling head is a priority task in trenchless drilling. We previously considered an acoustic method for monitoring the drilling head position in a directional drilling device. In this work, we consider a radar complex for monitoring the drilling head position from the surface of the earth with fixed transponder beacons. The radar method for obtaining such information allows the drilling process to be optimized by increasing the positioning accuracy, providing for constant automatic position monitoring, as well as reducing the time and financial costs.

Aim. To demonstrate the possibility of constructing a radar complex for obtaining information about positioning of the drilling head of a directional drilling installation based on transponder beacons distributed on the surface of the earth.

Materials and methods. The study was based on the physical principles used in mobile systems, i.e., determining the location of the probe and its parameters using radio signals emitted by the probe in the frequency range of tens of kHz, to minimize the influence of soil inhomogeneities.

Results. The possibility of using the radar method for obtaining the drilling head coordinates when monitoring its position during drilling operations was studied. The operational principle of such a radar complex was considered; the schemes of positioning transponder beacons on the surface of the earth and relative to the drilling head were developed; a technology for supporting drilling operations using this method was described.

Conclusion. We propose an approach to determining the drilling head coordinates and their automatic monitoring in real time. The proposed approach to constructing a high-precision radar information transmission complex can be used in the design and modernization of directional drilling equipment.

Introduction. At present, video data acquired in narrow spectral bands are widely used to improve the efficiency of diagnostics in various medical fields, laparoscopy in particular. Conventional laparoscopy uses images obtained in the white light. Images obtained in the visible range suitably depict the color and textural features of tissues. However, it is difficult for a physician to use visible images for distinguishing between lesion areas and normal tissues, largely due to their proximity in color and texture. The efficiency of lesion detection can be improved using fluorescence images, which clearly differentiate lesion areas from normal tissues. However, the use multispectral data implies the need to present the images obtained both in the white and fluorescence light to the physician. In this paper, we propose an image composition method based on visible and fluorescence images, which facilitates their analysis by physicians. A distinctive feature of the method is the use of CIEDE 2000 metric for image fusion, which takes the properties of human vision into account.

Aim. Development of a method for multispectral data visualization, which provides a physician with an image that combines white light data and a color-highlighted area of lesions.

Materials and methods. The proposed method consists of the following steps: preprocessing of images obtained in visible and fluorescence light; segmentation of the lesion area in the fluorescence images; generation of a pseudo-color image of the segmented lesion area; and fusion of the pseudo-color image with the image obtained in the white light.

Results. The proposed method forms an image that includes an image of the operation area obtained in the white light and a separated lesion area based on fluorescence information in the near infrared range. The image composite takes the properties of human vision into account. An experimental study of the method was carried out on actual laparoscopic images, involving endoscopists who were experts in subjective evaluation of video images. The method of paired comparisons was used to evaluated the presented images. The majority of experts preferred the fused image formed by the proposed method to those visualized simultaneously in the white and fluorescence light.

Conclusion. The developed method ensures generation of images with an increased diagnostic value.