Search

This paper is dedicated to the 90-th anniversary of Vadym Borysovych Razskazovsky, an outstanding scientist in the fields of radio engineering and radio science, holder of the titles and positions like DSc (Engineering), Professor, and Head of the Statistical radio physics department at the O.Ya. Usikov Institute for Radio Physics and Electronics within the Academy of Sciences of Ukraine.

Subject and Purpose. The development of radar methods for measuring liquid-drop precipitation characteristics is of great importance for studying physical processes in the atmosphere and for lots of applied problems to be solved. At the same time, an expe­rimental research of these methods in situ is essential to determine their frames and scope and estimate retrieval errors of the rain parameters. The purpose of the work is to evaluate effectiveness of the previously proposed method that is based on the parametrization of the distribution function of drops by size, uses averaged touch-probing data of the three-parameter gamma distribution of the parameters versus the rain intensity, and employs the double-frequency method of precipitation remote sensing. For its validation, the rain intensity results obtained by the radar sensing are compared with the data taken from the ground raingauge. Methods and Methodology. The measurement results gained by the proposed method are compared with the measurement results obtained by the standard technique. Results. An experimental study using the previously developed algorithm and with a refined double-frequency weather radar MRL-1 has been given to the double-frequency sensing of liquid-drop precipitation. The obtained results show that the proposed data processing algorithm for double-frequency sensing of liquid-drop precipitation is good at the rain intensity retrieval and makes it possible to estimate liquid precipitation amounts over long periods of time. Conclusion. The rain intensity measured with the use of meteo radar almost completely coincides, both qualitatively and quantitatively, with the data from the ground raingauge. The algorithm proposed by the authors for processing double-frequency radar sensing data on liquid-drop precipitation retrieves the rain intensity and, also, evaluates liquid-drop precipitation amounts.

Subject and Purpose. The article is devoted to the radio recognition of moving waterborne objects (sea-going ships). The problem lies in the lack of radar signatures, which is especially true for coherent radar in continuous mode, implying that more signatures for the waterborne object recognition is highly needed. An additional signature can be gained just by means of a simple mathematical processing of target reflection signals. This is particularly important for radio recognition systems in current use because this will hardly complicate the system structure. Hence, it will not affect its cost either. Methods and Methodology. The method developed for the retrieval of an additional radar signature characteristic of waterborne objects moving across a rough sea surface is based on a simple mathematical processing of a signal reflected from the moving waterborne object and taken from the phase output of coherent radar. The method approbation is by the mathematical modeling of signals at the phase detector output in the event of three waterborne objects such that have identical scattering cross sections but different periods of the side and keel vibrations. Results. Based on the mathematical modeling results, it has been shown that each of the local scattering centers keeps the ratio of the linear speeds of side and keel vibrations approximately the same for the same object. But the employed ratio takes different values for different objects. Conclusion. Having a single standard coherent radar in continuous mode and guided by the developed methodology, one can gain an additional signature for the target recognition, which is a ratio of the linear speeds of side and keel vibrations of the target. The suggested methodology can be used for the radio recognition of waterborne objects moving across a rough sea surface.

Subject and Purpose. Smoke, fog, avalanches, debris of collapsed structures and other optically opaque obstacles in both natural and man-made disasters make optical sensors useless for detecting victims. Electromagnetic waves of the decimeter range penetrate well almost all obstacles, reflect from the trapped people and return to the radar receiver. Due to the breathing and heartbeat, the human-reflected sounding signals get the Doppler phase modulation, which is an information signal. These information signals and their properties provide the subject matter for the present research with the aim to create optimal methods and algorithms of random event processing for the prompt location of survivors by rescuers. Method and Methodology. The method of stochastic analysis of the fluctuation Doppler spectra of reflected sounding signals shows that the information signals have properties of conditional Markov processes. Results. The problem of optimal nonlinear filtering of conditional Markov processes entering the radar signal processing unit has been examined closely. An optimal adaptive filter has been proposed to reduce the masking effect of interferences caused by non-stationary noises and sounding signal reflections from stationary objects. The optimality criterion is the minimum mean square error function whose current value is evaluated in real time during the filtering process as the statistics is accumulated. The filter coefficients are calculated by the recurrent, steepest descent algorithm. The real-time work is carried out through the use of fast Fourier transform algorithms. Conclusion. The structure of the optimal adaptive filter to be built into the radar signal processing unit has been developed. Real radar signals have shown that the optimal filtering during the signal processing in systems designed for detecting live people by their breathing and heartbeat facilitates the interpretation of the observed signals. Some spectra of real signals generated by human breathing and heartbeat are presented.

Subject and Purpose. The paper is devoted to the microwave propagation over the sea in the nearshore region. Emphasis is on microwave attenuation measurements in the semi-shade and deep-shade areas with a view to study conditions of the microwave propagation on a beyond-the-horizon path in the nearshore area using a radar method. Methods and Methodology. A radar technique, developed and tested, provides measuring a microwave attenuation coefficient along a 60 km long beyond-the-horizon path in the tropospheric surface layer. High-grade radar and Doppler radar beacons (racons) are employed. Of interest are experimentally obtained temporal dependences of signals from racons situated at different heights and, also, spatial field distribution curves from a steadily moving racon running a height 1 to 27 m for 25 minutes. Results. A prototype of high-grade X-band coherent continuous-wave (Doppler) radar has been designed and fabricated. A radar technique has been developed and tested for the analysis of microwave beyond-the-horizon propagation conditions in the shadow region, which involves continuous-wave (Doppler) radar and Doppler racons with a radar cross section (RCS) of about 60 m2. Conclusions. The technique proposed enables reliable tracking of racon responses up to a double radiohorizon range on over-sea paths. This technique can be used for radar calibrations when dealing with various location problems in the nearshore area, including detection and tracking small-size and low-flying targets and their radar identification.

Subject and Purpose. Answering the need for powerful high-frequency signal generation and desired radar range provision, pulsed magnetrons hold the current lead as part of radar transmitters. Yet there are some disadvantages, such as significant noise level and technological difficulties concerning the frequency tuning implementation. In this connection, a direct control of the pulsed magnetron frequency with the use of the Automatic Frequency Control (AFC) causes problems. And in the receiver, the AFC of the heterodyne rather than of the magnetron is more frequently used. The heterodyne frequency is maintained at such a level that the receiver is always tuned to the frequency of signal to receive. For various signal generation arrangements, the existing methods of frequency tuning with a frequency discriminator will be analyzed towards the following development of a principal electrical schematic diagram with gaining the operating characteristics of the frequency discriminator prototype on that diagram basis. Methods and methodology. The electrical schematic diagram is developed in terms of intuitive approach and analyzed by the mathematical modeling method. Results. The functional scheme of a frequency discriminator combining advantages of both single-cycle circuit (design simplicity and ease of tuning) and two-cycle circuit (null output voltage at a given frequency of the input signal and compensation possibilities as to the input voltage amplitude varying and interference) has been developed. The principal electrical schematic diagram of this new frequency discriminator has been reported together with the measured amplitude and frequency characteristics, dynamical figures, etc. Conclusions. The novelty of the proposed concept of a heterodyne AFC system built around a frequency discriminator has been confirmed. Its advantages over the known solutions have been shown.

Subject and purpose. The main factor which affects the development of modern marine radars and increase of their efficiency is the correct justification of the concept of construction and selection of technical requirements for the development of new devices. The purpose of this work is to analyze the existing methods of marine radar construction, generalize the results of long-term radio physical researches in different regions of the World Ocean and in the Black Sea water area as well, and on their basis to develop the concept for applied complex radar for surface situation control and navigation. Methods and methodology. During the development of construction concept and analysis of the offered radar features the method of mathematical modeling was used. Results. The concept for the complex radar system construction for surface situation control and navigation consisting of 3-cm radar and 8-mm radar with radiometer device is proposed. When choosing 3-cm wave range, the results of long-term radio physical researches conducted by Usikov IRE NASU in different regions of the World Ocean and the Black Sea water area were considered. The usage of 8-mm wave range allows one to carry out radar observation in the near-field zone where signals of 3-cm radar interfere and create strong reflections from the sea surface. The necessity to use 8-mm wave range radiometer is caused by the fact that reduction of the effective scattering cross section due to applied radio absorbing materials leads to increasing of object’s own radio brightness radiation. Therefore to detect barely visible (produced under Stealth technology) and low-sized targets the radiometer which allows to increase target contrast can be used. Conclusion. Conclusions on practical importance of the offered concept for construction of complex radar for surface situation control and navigation are made.

Subject and Purpose. The subject of the study is a measuring system consisting of several spatially separated receiving points and a transmitter emitting video pulse signals. The aim of the work is to create an effective algorithm for processing signals from a multi-position observation system under conditions of correlated jamming to solve the problem of the operational detection of mobile objects hidden behind optically opaque obstacles. Methods and methodology of work are based on the difference-distance-measuring principle of calculation of the target coordinates. The informative signal from the target is not identified by direct methods because of the multiple reflections of the sounding signal from the walls of the room and objects located inside it. The procedure for suppressing the interference reflections of the probing signal is developed. The accumulation of a signal and the removal of interference is carried out in real time by subtracting the alternating samples of the observed process from the signals of each receiving point assuming that the object is slow moving or practically unmoving during the time of sounding signal propagation from transmitter to target and back. The delay of the probing signal during its propagation from the transmitter to the target and from the target to each of the receivers has been estimated using the proposed peak factor criterion. The same criterion is used to reject the struck lines on the radar image of the target's trajectory. Results. A high-speed algorithm is developed which, at the condition of a relatively high signal-to-noise ratio, makes it possible to use the signal peak factor as a criterion for jammers suppression at the radar's image. The simplicity of signal processing allowed to continuously display the data in a user-friendly form. The continuity of measurements of the delays of the reflected signals from the target to the receiving points is ensured by polynomial approximation of the object trajectories relative to each of the receivers. Conclusions. The high energy characteristics of the observation system, the stability of the parameters during the measurements, and the high accuracy of the reflected waveform reproduction allowed us to use digital signal processing methods in real time. The simulation results are confirmed by data that were accumulated and averaged over a series of similar experiments.

Subject and purpose. At present, pulsed magnetrons are leaders in the use in the transmitters of radar stations which is caused by the need to generate powerful high-frequency oscillations and to provide a given range of radar. The disadvantages of magnetrons include a significant level of noise and difficulties in implementing frequency control. For this reason, when using automatic frequency control (AFC), problems arise in controlling the frequency of the pulsed magnetron. That is why AFC of heterodyne of the receiver rather than the one of the magnetron is most often used. The heterodyne frequency is maintained such that the receiver is always tuned to the frequency of the received signal. The purpose of this paper is to analyze the existing methods for tuning the heterodyne frequency of pulsed radars with a magnetron transmitter, to develop a concept for constructing a functional scheme and its practical implementation. Results. The functional scheme of the automatic frequency tuning system of heterodyne in radar receiver with a magnetron transmitter is developed. A frequency discriminator is used in AFC. The frequency discriminator combines the advantages of a single-cycle circuit (simplicity of design and tuning) and a two-cycle circuit (an output voltage equal to zero for a given magnetron frequency, as well as compensation of variations in the amplitude of the input voltage and interference). The practical implementation of the developed system is shown by the example of millimeter-wave band radar (40 GHz), where a generator based on a Gunn diode with varactor frequency tuning is used as the receiver heterodyne. In this paper, the electric scheme of a new frequency discriminator and its amplitude-frequency characteristic are shown. Methods and methodology. An intuitive method was used to develop an electrical schematic diagram. The analysis of the developed scheme was carried out using the method of mathematical modeling. Conclusions are made about the novelty of the proposed concept of constructing the AFC of heterodyne radar receivers with a magnetron transmitter and its advantages in comparison with known solutions

Measurement of precipitation amount is of great inte-rest for solution of many practical problems of national economy and agriculture. In this case, the inverse problem of recovering the rain intensity using radar methods is an incorrect problem of mathe-matical physics and is described by a nonlinear integral equation. An approach for solving the integral equation of the electromagnetic waves scattering by a polydisperse medium of water drops is considered by means of double frequency remote sensing in the microwave range. Numerical simulation for retrieval of rain intensity in the range of 1…30 mm/h is performed for operating wavelengths 0.82 and 3.2 cm. It is shown that the proposed approach permits to retrieve the rain intensity with an error less than 20 % for intensities > 5 mm/h and with an error up to 60 % for light rains (less than 5 mm/h).

The adequate models of information signals and noise have been developed to solve the actual problem of the synthesis of hardware and software for operative detection of affected peop-le in man-made or natural disasters. It is shown that at low frequencies, where are placed the spectral components of the information signal generated by breathing and heartbeat, an adequate model of the fluctuation noise is a flicker noise model built on the basis of recurrent equations of Perron-Frobenius operator. The spectral characteristics of the information signal and noise are investigated. The information signal model is built on the theory of periodically correlated random processes and verified on experimental data. A signal processing algorithm has been proposed. The algorithm is based on a process of cross-sampling summing. A criterion to assess the duration of the period of the signal is proposed. The criterion is a function of the signal dispersion from the lattice function period. The ergodic property of the process on an equidistant grid is theoretically proved and experimentally confirmed. The optimal estimate of period duration is an argument of the global maximum of the polymodal criterion function. The simulation results are confirmed by the experimental data.