Dmytro Vavriv

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Papers by Dmytro Vavriv

Operating characteristics of resonance amplifiers with distributed interaction and preliminary beam modulation

Three-frequency resonances in single-mode systems

2016 9th International Kharkiv Symposium on Physics and Engineering of Microwaves, Millimeter and Submillimeter Waves (MSMW), 2016

We review recent results on the interaction of low- and high-frequency oscillations that lead to ... more We review recent results on the interaction of low- and high-frequency oscillations that lead to arising of three-frequency resonances in nonlinear oscillators. The Duffing oscillator and the Van der Pol oscillator both with modulated natural frequency and a high-frequency harmonic forcing are considered as examples to illustrate and study this phenomenon. It is shown that such interaction enables an efficient control of the oscillators dynamics and their properties. The formation of bistable states and synchronous oscillations is considered in detail.

The modern radio astronomy network in Ukraine: UTR-2, URAN and GURT

Experimental Astronomy, 2016

The current status of the large decameter radio telescope UTR-2 (Ukrainian Tshaped Radio telescop... more

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The theory of resonant amplifiers with prolonged interaction. IV

Millimeter-Wave Magnetron Transmitters for High-Resolution Radars

AIP Conference Proceedings, 2006

Experience in the development and application of transmitters for coherent radar systems based on... more Experience in the development and application of transmitters for coherent radar systems based on millimeter-wave magnetrons is summarized. Design approaches to the development of highly efficient transmitters for frequencies of 36 GHz and 95 GHz with power level of 30 kW and 4 kW, respectively, are discussed. Meteorological Doppler radar systems based on such transmitters are described as examples of applications of the transmitters.

SAR processing under unstable flight conditions

2015 IEEE 1st International Forum on Research and Technologies for Society and Industry Leveraging a better tomorrow (RTSI), 2015

Synthetic aperture radar (SAR) processing techniques and approaches, which are required for the o... more Synthetic aperture radar (SAR) processing techniques and approaches, which are required for the operation under unstable flight conditions, are described in the paper, including frame-based data processing, compensation of motion errors, and autofocusing. Performance of the methods is illustrated on radar data obtained with Ku-band and X-band airborne SAR systems.

A theory of long-interaction resonant amplifiers. II

Radiofizika, 1985

New type of instability in resonance amplifiers

Radiotekhnika, May 1, 1988

Lowering the threshold for bistability

2015 European Microwave Conference (EuMC), 2015

A novel mechanism of the bistablity onset based on a low-frequency modulation of the natural freq... more A novel mechanism of the bistablity onset based on a low-frequency modulation of the natural frequency of a harmonically forced nonlinear oscillator is presented. It is shown that such modulation results in arising of an additional bistable state, which has a lower threshold for bistability with respect to the forcing amplitude as compared to the modulationless case. This lowering is caused by the high- to low-frequency interaction. A theory of this phenomenon is presented by considering dynamics of the Duffing oscillator as an example. The corresponding threshold values of the amplitude are found analytically. A comparative analysis of different types of bistable states in such oscillator is carried out as well. The results are important for such applications like storing binary data in digital electronics.

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Noise factor of resonant amplifiers with distributed interaction

Radiophysics and Quantum Electronics, 1988

NOISE FACTOR OF RESONANT AMPLIFIERS WITH DISTRIBUTED INTERACTION D. M. Vavriv and O. A. Tret'yako... more NOISE FACTOR OF RESONANT AMPLIFIERS WITH DISTRIBUTED INTERACTION D. M. Vavriv and O. A. Tret'yakov UDC 621.385.6 The problem of electron beam shot and thermal noise conversion in resonant systems with distributed interaction is solved in a self-consistent formulation. Expressions are obtained for output oscillation amplitude and phase fluctuation spectra. The noise figure is minimized. The perspectives for developing narrow-band lownoise amplifiers based on such systems are discussed. i. Formulation of the Problem. The analysis of resonant amplifiers with distributed interaction performed in [1-3] demonstrated that because of the regenerative interaction mechanism between particles and field in such devices high gain can be achieved with a small number of stages. When one considers the high selectivity of amplifiers of this type it becomes interesting to consider the possibility of using these devices for weak signal amplification in the short wavelength portion of the uhf spectrum. Orotron amplifiers using open oscillating systems are obviously the most promising for this application. However to evaluate the capabilities of an amplifier with several stages of this type it is first necessary to analyze their noise characteristics, which so far have remained unstudied.

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Recent advances in theory and performance of millimeter-wave magnetrons

25th International Conference on Infrared and Millimeter Waves (Cat. No.00EX442), 2000

Spatial-harmonic magnetrons with cold secondaryemission cathode are candidates for pulsed high-po... more Spatial-harmonic magnetrons with cold secondaryemission cathode are candidates for pulsed high-power sources in the 3-mm and 2-mm wave frequency bands and even below. We have recently developed a nonlinear beam-fiei I interaction model in order to optimise their performance and to study the frequency and power limits. Both simulated and experimental results promise excellent performance of such miniaturized tubes which have reached a mature state for radar applications in the 2-mm wave band.

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Advantages of doublet modes for high-power millimeter-wave generation

10th International Conference on Mathematical Methods in Electromagnetic Theory, 2004.

Absfracl - The application in vacuum electron oscillators of degenerated modes, which are split d... more Absfracl - The application in vacuum electron oscillators of degenerated modes, which are split due to absence of the exact symmetry of oscillatory circuits, is considered. General peculiarities of the interaction of electron flows with such modes are described. The spatial-harmonic magnetron oscillator is used as a practical example of the study. It is shown that the usage of doublet

Fractal dimensions: Computational problems

USSR Computational Mathematics and Mathematical Physics, 1989

A comparative analysis is performed of the basic methods for calculating fractal dimensions and a... more A comparative analysis is performed of the basic methods for calculating fractal dimensions and a new computational technique is proposed. A relationships is derived between the invariant distribution function and the probability distribution function of the distances between points on a strange attractor. The effect of boundaries and singularities in the invariant distribution function on fractal dimensions is investigated. Fractal dimensions are computed for particular systems with chaotic behaviour.

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Amplification regimes of the orotron: A single-resonator amplifier

Physical Review E, 1998

A self-consistent, nonlinear model of orotron amplifiers is proposed for investigating single-sta... more A self-consistent, nonlinear model of orotron amplifiers is proposed for investigating single-stage and multistage amplifiers. The single-resonator amplifier is studied in detail including linear and nonlinear modes of amplification. A comparative study of both collective and single-electron interaction regimes is performed. The fundamentals which determine the level of amplifier performance are identified, and limiting output characteristics of the amplifier are determined. The theoretical results are compared with experimental data known to date. ͓S1063-651X͑98͒02605-1͔

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Moving target detection with multi-look SAR

2014 20th International Conference on Microwaves, Radar and Wireless Communications (MIKON), 2014

The problem of detection of moving targets and estimation of their parameters by means of a multi... more The problem of detection of moving targets and estimation of their parameters by means of a multi-look single-antenna synthetic aperture radar is considered. The detection of moving targets is based on the displacement of the target images with respect to the static ground scene on the consequent looks. A system of linear algebraic equations has been derived in order to estimate the range to the moving target, the module and the radial component of the relative velocity vector of the target. It is shown that for the target moving uniformly and rectilinearly along a known path its location and own velocity can be found from a system of quadratic algebraic equations. The proposed approach is illustrated with both simulated and real data.

Identification of Saturn Lightnings Recorded by the UTR-2 Radio Telescope and Cassini Spacecraft

Radio Physics and Radio Astronomy, 2011

The Saturn Electrostatic Discharges (SED) simultaneously recorded in the initial period of storm ... more

Ground-based and space observations of planetary thunderstorm activity

2010 INTERNATIONAL KHARKOV SYMPOSIUM ON PHYSICS AND ENGINEERING OF MICROWAVES, MILLIMETER AND SUBMILLIMETER WAVES, 2010

After twenty-five years of study on Saturn electrostatic discharges (SED) with the aid of spacecr... more

Ground-based and spacecraft observations of lightning activity on Saturn

Planetary and Space Science, 2012

In late 2007, Saturn electrostatic discharges (SED) were simultaneously observed at the radio tel... more In late 2007, Saturn electrostatic discharges (SED) were simultaneously observed at the radio telescope UTR-2 and with the Cassini spacecraft. Observations at UTR-2 were performed with a multichannel receiver in the frequency range 12–33MHz, and those performed on Cassini—with a swept frequency receiver that is part of the RPWS (Radio and Plasma Wave Science) instrument in the frequency band 1.8–16MHz.

High-resolution radars at the Institute of radio astronomy of the NAS of Ukraine

A review is given of recent activities undertaken in the Institute of radio astronomy of the Nati... more A review is given of recent activities undertaken in the Institute of radio astronomy of the National academy of sciences of Ukraine for the development of high-resolution radars. The radars developed include 95 and 36 GHz cloud radars and an airborne, Ku-band SAR radar system. They are capable to perform real-time, high-resolution measurements. The set-up of these instruments, the novel technical solutions, and the signal processing technique introduced are discussed. The results obtained with such instruments during measurement campaigns are presented as well.

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