Introduction. Numerous modern infocommunication systems are based on the spread spectrum technology, i. e., on the use of signals with a large bandwidth-duration product. Many such systems implement discrete signals, which are sequences of standard pulses manipulated in phase and amplitude. The design of code sequences for such signals is a fairly knowledge-intensive task requiring a serious mathematical apparatus. This review presents the results of Saint Petersburg Electrotechnical University school in the field of synthesis of code sequences with ideal or nearly ideal autocorrelation, as well as code ensembles for CDMA networks.

   Aim. To acquaint the reader with the results of long-term research carried out by Saint Petersburg Electrotechnical University school in the field of discrete signal design.

   Materials and methods. The materials under review included the publications of specialists from the Radio System Department of Saint Petersburg Electrotechnical University and those published by domestic and foreign researchers on the corresponding topics. The major focus was to review the most theoretically significant texts published in leading domestic and foreign journals over the past four decades, leaving applied studies, copyright certificates and patents outside the scope of the review. At the same time, the review included those foreign publications of applied nature that are significant for the development of information and communication projects.

   Results. The reviewed publications significantly expand the range of discrete signals that are promising for wireless infocommunication applications.

   Conclusion. Solutions of a number of the studied topical problems to design sequences with the necessary metric properties are of an original nature and great practical importance.

   Introduction. In the past few years, the rapid development and widespread use of unmanned aerial vehicles (UAVs) for solving a variety of tasks has created new threats. The problem of ensuring the safety of protected objects, especially in the area of critically important objects or in places with difficult ornithological conditions (airports, wind power facilities), is of particular importance. In this regard, the issue of detecting small air targets and recognizing their type and degree of danger is acquiring greater importance. This paper presents an algorithm for recognizing air targets based on
artificial intelligence technology. The results of a comparative analysis of decision-making methods for recognizing small UAVs and birds based on their trajectory features are presented. The results obtained can be used in the development of systems for recognizing classes of small airborne targets in existing and future radar stations.

   Aim. Development of an algorithm for recognizing small air targets by trajectory features based on machine learning. Implementation and evaluation of the quality of decision-making methods in a given recognition problem.

   Materials and methods. Experimental data on the trajectories of UAVs and birds obtained in a passive bistatic radar system are used. The trajectory parameters of the targets and their statistical characteristics are calculated; a set of features for recognition is formed. Using the MATLAB software package, a program for implementing the recognition algorithm and analyzing the quality of decision-making methods was developed.

   Results. An algorithm for recognizing air targets based on artificial intelligence technology is presented. A comparative analysis of the six most common recognition methods based on machine learning (Naïve Bayes, decision trees, k-nearest neighbors, neural network recognition algorithm, support vector machine, random forests) was carried out, which showed that, under the conditions of this problem, the most effective are k-nearest neighbor method and support vector machine.

   Conclusion. The presented methods can be used to directly determine the class of targets from a set of marks of their trajectories. Further research will be aimed at developing and implementing a real-time recognition algorithm.

   Introduction. Protection of radio electronic equipment (REA) against various electromagnetic interferences is an important aspect of electromagnetic capability. Among interferences for REA, ultra-short pulses of picosecond and nanosecond ranges represent the highest danger due to their high voltage, short duration, and wide spectrum. One effective protection measure consists in the use of bandpass devices based on modal decomposition, such as modal filters (MF). This requires an analysis of distortion of the temporal response of bandpass devices, which is usually carried out numerically. However, even for simple configurations, this approach is associated with high computational costs. Yet simple analytical time-response models are acceptable in some cases. In the initial design stages, such models are extremely useful in providing a preliminary solution and a rapid assessment of response distortions. Therefore, comparison of time responses obtained by numerical methods and analytical models appears an important research task.

   Aim. To compare the time responses obtained by quasi-static analysis and analytical models.

   Materials and methods. Analytical models for computing time responses based on a modal analysis technique were considered. A quasi-static modeling of a microstrip line (MSL) with two additional symmetrical conductors on top in the TALGAT system was carried out.

   Results. Analytical models are proposed for an MSL with two additional symmetrical conductors on top taking different boundary conditions at their ends into account. The accuracy and reliability of the proposed models are verified by comparing the time responses obtained by quasi-static analysis and the proposed models. The results obtained showed good agreement.

   Conclusion. It is shown that an MSL with two additional symmetrical conductors on top can be used as an MF under different boundary conditions at the ends of these conductors. The proposed models allow the shape and amplitude of the response to be estimated with acceptable accuracy, reducing time and computational costs.

   Introduction. Patch antennas have found wide application in UAVs due to their numerous useful properties. However, since such an antenna system is essentially a resonator, the problem of its matching remains unresolved. The existing publications mostly deal with specific cases and report the typical values of the matching band of 5–7 %, which cannot be considered sufficient when there is a need to use the signal spectrum of up to hundreds of MHz. Therefore, research aimed at using more efficient methods of broadband matching could be of interest for engineers.

   Aim. To develop a broadband matching technique based on the generalized Darlington synthesis method using flexible approximating functions (AF) for load models with resonant properties.

   Materials and methods. The capabilities of the generalized Darlington synthesis method are extended AFs with increased variation properties. Flexible control of AF weight coefficients makes it possible to realize both smooth and wave frequency characteristics. The method is analytical and does not use iterative procedures. The mathematical apparatus of the method is based on an analysis of deductions in the zeros of the load resistance transfer function.

   Results. Flexible approximating functions were established to be effective for synthesis of matching circuits with resonant properties. Solutions for matching the loads with multiple transfer zeros both at the origin and in infinity were obtained. The opportunity of creating patch antennas with a matching layer up to 40 % and more was demonstrated.

   Conclusion. The results obtained for the SWR of patch antennas show that the potential estimates of matching limits are available only for analytical methods.

   Introduction. The signal recognition task for the purposes of RF spectrum management can be solved using a signal recognition algorithm with detection at two intermediate frequencies. This algorithm is based on time–frequency analysis using fast Fourier transform (FFT) and signal envelope processing. Due to the relative simplicity of transformations, this algorithm is implemented on commercially available field programmable gate arrays and allows processing received signals in near real-time. However, the justification of the algorithm parameters providing effective signal recognition by the criterion of minimizing the signal-to-noise ratio (SNR) has not performed so far.

   Aim. Justification of parameters of the developed signal recognition algorithm, providing the minimum required SNR at the algorithm input.

   Materials and methods. The efficiency of the developed algorithm was estimated by computer simulation in the MATLAB environment.

   Results. The influence of the parameters of functional blocks and received signals on the efficiency of the developed algorithm was investigated. For chirp, simple pulse, binary, and quadrature phase shift keying signals, the following parameters are recommended: a pulse duration of 5…20 μs; a chirp rate of 0.8…24 MHz/μs; a code duration of 0.5…1 μs. For these signal parameters, the parameters of the algorithm ensuring its efficiency according to the given criterion are as follows: the number of FFT points equals 1024; the Hamming weight window; bandwidths of band-pass filters are 4 MHz; signal envelope amplitude averaging coefficient equals 0.15…0.25.

   Conclusion. The algorithm with the scientifically valid parameters can be used for recognition of signals at the input minimum SNR for the given types and parameters of signals.

   Introduction. The active development of satellite communication networks determines the need for new antenna systems for ground terminals. The Sphere Federal program implies the commissioning of new satellite constellations for communication and remote sensing of the Earth. The Skif (providing broadband Internet access) and Express-RV (providing the Internet and communications for Arctic) satellite constellations are not geostationary, thus requiring constant satellite tracking even for stationary terminals. Deflecting structures operating on the principle of quasi-optical beam control make it possible to develop scanning antenna systems for organizing continuous satellite communications.

   Aim. Investigation of various types of dielectric structures for radiation pattern deflection and scanning antenna systems on their basis, as well as identification of a configuration with improved characteristics compared to the ideal structure in the shape of a dielectric wedge.

   Materials and methods. Mathematical modeling, electrodynamic modeling using CAD by the finite element method and the finite integration method, as well as an experimental study of an antenna system prototype in an anechoic
chamber by measuring methods in the far-field and near-field of the antenna.

   Results. Electrodynamic simulation was carried out for three types of dielectric structures, analogues of a dielectric wedge, including a structure assembled from various dielectrics of fixed sizes with different dielectric constants; a structure of triangular dielectric plates; and a perforated dielectric structure. In addition, scanning antenna systems based on the presented configurations were analyzed. Radiation patterns were obtained for all structural types for various rotation angles of the deflecting systems. The structure assembled from various dielectrics of fixed sizes with different dielectric constants was found to possess the most optimal characteristics. This structure was used to develop a model for experimental confirmation of the conducted electrodynamic simulation. The maximum tilt angle of the radiation pattern was about 60°, the decrease in the directivity relative to the maximum value was 6 dB; for tilt angles up to 55°, the directivity degradation did not exceed 4 dB, the level of the side lobes did not exceed –12 dB (calculated) and –14 dB (measured).

   Conclusion. The results of studies into various types of structures for quasi-optical beam control of the radiation pattern show the possibility of using these configurations when creating low-profile antenna systems with wide-angle mechanoelectric scanning for organizing satellite communications for both mobile and stationary consumers using medium earth orbit spacecrafts.

   Introduction. Modern computing and electronic devices are constructed on the basis of radio-electronic components, such as processors, graphics processing units, etc. During operation, these components emit tens of watts of thermal energy. Therefore, effective excess heat removal from both semiconductor electronic devices and electronic systems as a whole through the use of passive or active cooling systems represents an important research problem.

   Aim. To study the influence of the configuration and shape of external ribs of sealed enclosures of electronic devices, which use solely passive cooling systems inside, on the efficiency of heat removal from the processor for each
enclosure design under consideration based on their comparative analysis.

   Materials and methods. Simulation experiments were carried out using 3D parametric models of various device types, which were developed in the SolidWorks Flow Simulation software environment. These models differed in terms of configuration of thermal channels formed by the external enclosure ribs.

   Results. The conducted simulation experiments allowed the authors to study the cooling process of processors installed in modern electronic devices. The influence of the configuration and shape of the enclosure ribs on excess heat removal from the processor was studied in a passive cooling mode and when blowing the devices with air moving from above (perpendicular to the cover) or laterally (parallel to the cover) with a gradual increase in a processor power from 10 to 25 W. A ribbed enclosure with passive cooling was shown to ensure a more effective heat removal from a 10 W processor compared to a non-ribbed enclosure (the temperature drop is 4.1 °C). For a 25 W processor, this value comprises 11.01 °C. When blowing the device, the direction (perpendicular or parallel) of air movement significantly affects the cooling efficiency of the heated surface (with a processor power of 45 W, the difference is more than 10 °C).

   Conclusion. The developed 3D models effectively simulate the cooling system of heat-loaded high-power radio-electronic components located in sealed enclosures, due to the implementation of their external ribbing.

   Introduction. The requirements for the performance of measuring devices, including their operating frequency, are constantly becoming stricter. This encourages the creation of wide-band microcircuits for application in microwave blocks of devices, such as vector network analyzers (VNA) and spectrum analyzers (SA). One of such microcircuits, used in the receiver system, is a frequency mixer. The operating range of the mixer determines the operating range of the measuring instrument.

   Aim. Research and development of an ultra-wideband integrated circuit for a 13…67 GHz frequency mixer based on the GaAs QSBD technology by Micran JSC.

   Materials and methods. An analysis of existing classic and modified circuit transformers used in mixers was conducted. A modification of the transformer circuit, which allowed a frequency range of 10…70 GHz to be achieved,
was proposed. Based on the obtained transformer and GaAs diode technology of Micran JSC, a complete mixer topology was developed and produced. An electrodynamic analysis of the integrated circuit was carried out; measurements were performed using a VNA up to 67 GHz.

   Results. A wideband mixer with a frequency range of 10…67 GHz is developed. A circuit design is proposed based on a balanced circuit with modified transformers and an intermediate frequency output circuit. The calculated dependences and measurement results of the integrated circuit of the mixer are presented. The mixer exhibits a conversion loss of less than 10 dB in the range of 10…67 GHz.

   Conclusion. A new broadband transformer with a range of operating frequencies from 10 to 70 GHz was developed. On its basis, a mixer microcircuit was simulated and manufactured. This microcircuit can be used in the receiving and transmitting units of modern measuring instruments. In terms of its characteristics, the proposed microcircuit is an analog of the Marki Mikrowave MM1-1467L mixer.

   Introduction. Generalized extreme value (GEV) distributions represent a universal description of the limiting distribution of the normalized local maxima statistics for independent and identically distributed data series. Extreme value distributions are commonly classified into three different types representing different functional forms and thus varying in shape, also known as types I, II, and III. Thus, attribution of some observational data series to a particular type of its local maxima distribution, as well as fitting of the distribution parameters, provides certain information about the laws governing the underlying natural or technogenic process. Radar-based remote sensing techniques represent a ubiquitous tool for analyzing large patterns of the sea surface and determining the parameters of the waves. In turn, understanding the laws governing the extreme values in the rough sea surface obtained from their radar images followed by evaluation of their distribution parameters, depending on the wind speed and direction, as well as the presence of surface currents and swells, can be useful for predicting wave height.

   Aim. Analysis of the functional forms governing the local extreme value distributions in a rough sea surface for the given wind and swell parameters based on computer simulations.

   Materials and methods. For the rough sea surface simulated by an additive harmonic synthesis procedure, the local extreme value distribution was fitted using the least-mean-squares technique. The fitted parameters were then used for their classification according to the three predetermined types.

   Results. Computer simulations of a rough sea surface with combined wind and swell waves were performed. It is shown that the distribution of local maxima in the absence of swell waves could be well approximated by the
Weibull (type III GEV) distribution, with the parameters explicitly depending on the wind speed. At the same time, no significant dependence on the sea depth was observed. On the contrary, in the presence of additional swell waves, the distribution of local extrema could be rather attributed to the Fréchet (type II GEV) distribution, with the parameters additionally depending on the angle between the wind and swell waves.

   Conclusion. The laws governing the distributions of local wave extrema in rough seas are in a good agreement with the theoretical GEV approximations, with the distribution parameters being deductible from the key features of the waves. This indicates the predictability of wave height extrema from sea surface measurements, which can be performed based on remote radar observations.