ANALYTICAL SOLUTION OF THE PROBLEM OF CAVITIES DIPOLE MODES COUPLING THROUGH SMALL HOLE
M. I. Ayzatskiy, K. Yu. Kramarenko
The problem of the cavity dipole modes coupling is of great practical significance, since it is the basis for the description of non-axial oscillations in disk-loaded waveguides. These oscillations are responsible for the transverse displacement of the accelerated beam and, consequently, for transverse instability in linear resonance accelerators. Until recently, there was no method based on the rigorous electrodynamic approach for calculation of coupling coefficients of the cavity dipole modes under various assumptions about the geometry of the aperture and cavities. Therefore, these coefficients were calculated by approximate methods based on the solutions of electrostatic and magnetostatic problems. Electromagnetic fields in different regions were considered as a complete set of eigenfunction consisting of solenoidal and potential subsystems. Infinite sets of algebraic equations for the expansion coefficients of the field at the aperture obtained by using boundary conditions were transformed into systems of dual integral equations. Analytical solutions of these integral equations are obtained. It is shown that there is no zero approximation in the expansion of the tangential component of the electric field at the aperture in the small (~a) parameter. The tangential component of the electric field is proportional both to the tangential components of the magnetic field of TM110 and TE111 modes (~a/l, where l is the wave length) and to the normal (to the plane of the aperture) component of the electric field of the TM110 mode (~a/b, where b is radius of the cavity). The coupling coefficients of TM110 and TE111 modes are obtained. It is shown that the coupling coefficients, defined up to a3, depend only on the solenoidal component of electric field at the aperture. In contrast to the widely used heuristic approach based on the selection of the parameters of coupled circuits chain, the proposed approach makes it possible to describe the characteristics of an axially asymmetric oscillations in slow-wave structures and the process of their excitation by high-current electron beam more accurately.
THE AUTOCOLLIMATION MODE OF 3D GAUSSIAN BEAM REFLECTED FROM THE 2D-PERIODIC ARRAY OF SHORTED RECTANGULAR WAVEGUIDES
A. V. Gribovsky, O. A. Yeliseyev
While making the up-to-date spectroscopic instrumentations, mainly the reflective diffraction arrays operating in the autocollimation mode are used. The use of reflective arrays of waveguide type in autocollimation mode for designing various devices can give an essential advantage, in comparison with arrays of not waveguide type. Examinations of dispersion of Gaussian wave beams on two-dimensional-periodic array in an auto-collimation mode have not been conducted before. Exploring performances of dispersion of an electromagnetic field at slope of 3D Gaussian wave beam on 2D-periodic structure it is necessary to determine the angles under which not specular beam is spread. To construct energy dependences of a beam, far-field pattern the new algorithm is required, which differs from the algorithm used during the analysis of energy properties of a specular beam. The autocollimation mode is explored at reflection of three-dimensional Gaussian wave beam on 2D-periodic array from the short-circuited wave guides of rectangular section. Effects for slope cases p- and s-polarized beam of circular section on an array with a rectangular end are presented. The dependences of power reflectivities on the length of the short-circuited wave guides for specular and not specular beams are calculated. The dependences of pattern shape of reflected beams in far zone on parameters of an array and an incident beam are explored. The 3D patterns on power of specular and not specular beams in far zone are calculated. The physical explanation of effects of redistribution of energy between a specular and not specular beam is offered. The effect of pattern split of a reflected beam is established. For the first time energy performances and 3D patterns in far zone for not specular beam are gained. The analysis of the gained effects allows to determine at what parameters of an incident beam and a reflective array approximation of an incident field of a beam by a plane wave field is possible.
RANDOM LINEAR ANTENNAS WITH MANAGED RADIATION PATTERN
A. A. Maystrenko, S. S. Melnik, G. M. Pritula, O. V. Usatenko
In the paper the linear arrays widely used both in theoretical studies and practical applications are studied. It is assumed that the intensity of the dipole radiators and the distances between them are random variables, which significantly complicates the problem. It is shown that the intensity of the interference of the radiation field can be expressed in terms of correlation functions of random variables. The method for constructing two random binary sequences with given autocorrelation and correlation functions is proposed. This method allows solving the inverse problem of synthesis of random antennas for a given pattern. The results of numerical implementation of the method of constructing such antennas that can be put in use are presented.
MODEL OF MULTIPATH PROPAGATION OF MILLIMETER RADIO WAVES ABOVE MARINE SURFACE AT STRONG SHADING
V. B. Razskazovskiy, Yu. F. Logvinov
Importance of model of distribution of radio waves above a marine surface at strong shading conditioned by practical meaningfulness of this task and necessities of fundamental science for the study of physical processes at distribution of waves. The existent methods of calculation the radio waves propagation above sea surface use a model on the average flat interfacial area air – water with disturbances that are wind waves. However such terms of distribution of radio waves rarely enough meet in practice. We are investigating of the case of very small grazing angles and marine wave of such high, when the slopes of waves and intervals between them are shaded, and the electromagnetic field have interaction only with their tops. In the point of interaction with them radio waves because of small angle of grazing and great curvature of surface for description of the reradiated field the approaching of geometrical optics can not be used. Coordinates and curvature of the unshaded elements that are the tops of the marine waves were calculated by the method of numeral modeling. It is shown that the radiated from them electromagnetic field is a sum of Fresnel diffracted and specular reflected waves from cylindrical (in our two-dimensional case) surfaces. These were appraised for the radio waves of Ka-band (8-mm wavelength): the power distribution of reradiating on length of route, the angular spectrum of waves coming to the aperture of receiving antenna were appraised. Knowledge of these is needed for the analysis of work of direction-finding radio systems. In-process got and analysed to the feature of distribution on length of route and on the corners of arrival pithily reception of powers coherent and non-coherent component by the radiated by the surface of sea the fields substantially influencing on exactness of the systems of measuring of angular coordinates of radiants, including using the modern methods of spectral evaluation.
APPLICATION OF “BUREVESTNIK ZG” RADAR FOR BEYOND-THE-HORIZON DETECTION OF THE SURFACE OBJECTS
V. P. Dzyuba, A. D. Dorichenko, V. D. Yeryomka, A. F. Zykov, L. P. Milinevskij, I. M. Mytsenko, A. N. Piven, O. I. Prokopenko, À. N. Roenko, D. V. Roskoshnyj
One of the problems in the area of radio wave propagation and radar design is creation of radar facilities for navigation in the regions of the World Ocean with intensive shipping. Ukrainian radio-electronic industry has a large experience in development of different purpose radar systems, one of that is the radar “Burevestnik”. This radar is used to control and observe marine surface situation on the naval border check-points of Ukraine. In the paper it is suggested to modernize radar “Burevestnik-1” for navigation and beyond-the-horizon detection of the surface objects. The possibilities of “Burevestnik ZG” effective application for beyond-the-horizon detection of the surface objects in the districts of the World Ocean are estimated. To illustrate the latter the centimeter radio waves attenuation factor database, created in IRE NASU on the base of experimental results, is used. Statistical distribution functions of the “Burevestnik ZG” radar coverage range in the districts of the World Ocean are determined. Comparison with experimental data for stationary navigation radars “Don”, “Nayada” and “MRL-5” is conducted. Finally a conclusion, that radar “Burevestnik ZG” can be used in the regions of the World Ocean for navigation and beyond-the-horizon detection of the surface objects, is made.
CORRECTION OF RADIOMETRIC DISTORTIONS IN IMAGES IN THE CASE OF SAR PROCESSING WITH RANGE-DOPPLER ALGORITHM
I. M. Gorovyi, O. O. Bezvesilniy, D. M. Vavriv
Synthetic aperture radar (SAR) is an effective instrument for the formation of high-resolution images of the earth surface. Trajectory instability is one of the factors that affect the quality of the obtained images. The problem is that even in the case of application of a common motion compensation procedure, which is necessary for synthetic aperture formation, instabilities of the antenna beam orientation are still left uncompensated. This leads to radiometric distortions in SAR images. This problem is especially critical in the case of SAR processing with frame-based algorithms based on FFT (for example, the range-Doppler algorithm), which assume the constant antenna beam orientation within the large data blocks. In this paper the method of radiometric correction of SAR images is considered in the case of processing of SAR data in the frequency domain. Its idea is based on the formation of extended number of looks which corresponds to the broadening of the processed Doppler bandwidth. It is shown that such broadening allows to compensate the influence of two effects: changes of the real antenna beam orientation angles in respect to the aircraft velocity vector and also the possible additional broadening of the Doppler bandwidth of the received signals due to the application of the common motion compensation procedure. The obtained extended number of looks is used for the restoration of the multi-look SAR image without radiometric errors. The introduced methods of radiometric correction are an efficient alternative to expensive antenna stabilization systems and actively used in operating SAR systems. The efficiency of the developed algorithms is illustrated by real SAR data examples.
INTERACTION OF ELECTROMAGNETIC SIGNALS WITH AN ANTENNA MADE OF A GAS-DISCHARGE PLASMA
V. V. Ovsyanikov, S. M. Moroz
The interaction of electromagnetic signals with the plasma antenna is an important task of radiophysics and electronics, as they are used in various branches of radio engineering, including the armed forces. Despite the considerable number of publications on plasma antennas, currently the problem of the influence of mercury vapor on their electromagnetic characteristics is not covered. A method for calculating the conduction of cold plasma with the addition of mercury vapor is provided. The characteristics of plasma antennas with mercury vapor and without them in the two frequency bands in the software environment FEKO are calculated. The effect of mercury vapor on the parameters of plasma antennas is analyzed. The calculations have shown that the introduction of mercury vapor into the plasma antenna leads to a significant reduction in its efficiency and the changing characteristics of VSWR, especially with increasing frequency electromagnetic signals. To improve the parameters, especially the efficiency of the studied antennas, the recommendations to reduce the amount of mercury in them have been given. The considered antennas can be used for installation on aerospace vehicles.
ANALYSIS OF SURFACE WAVES PROPERTIES IN FINITE PERIODIC STRUCTURE NEAR THE EXCITON BANDS
V. V. Baibak, A. A. Bulgakov
The study of THz electromagnetic waves is an intensively developing trend in radiophysics. However, terahertz is experimentally harder to reach and it is less studied than the bordering microwave and infrared ranges. In this paper we solve the problem of the propagation of surface electromagnetic waves in a layered-like periodic structure, that contain layers with excitons, in the terahertz wave band. We consider the dispersion properties of electromagnetic waves for infinite and for bounded periodic structures. We analyze the possibility of the existence of surface electromagnetic waves that can propagate along the surface of the bounded sample in areas where body waves do not propagate. With complex Poynting theorem it is shown that the surface waves can exist independently or simultaneously on each surface of the structure. The obtained results allow us to analyze the features of the surface, attached to a periodic pattern. This makes possible to study the quality of thin films on solid surfaces, the surfaces of biological materials, etc.
ACOUSTIC SPIN-WAVE RESONANCES IN STRAINED CRYSTAL OF IRON BORATE
V. I. Khizhnyi, T. M. Khizhnaya, V. V. Tarakanov, A. P. Koroluik
Antiferromagnet and simultaneously “weak” ferromagnet iron borate FeBO3 possesses unique characteristics. Its high Neel’s temperature and tremendous effective uniform exchange field result in a strong magnetoelastic coupling. The peculiarities of dynamic effects of strong magnetoelastic coupling in the iron borate presents substantial physical interest, as dynamic and static elastic deformations can change magnetic properties of crystal. At propagation of longitudinal hypersound wave along the axis of symmetry Ñ3 of FeBO3 crystal in the magnetic field, the oscillation structures of amplitude and phase of transmission coefficient have been found out by authors. Previously, the authors offered the physical model of phenomenon. It consists in that in the mode of standing sound wave a magnetic modulation (incommensurable) structure can emerge in a sample. In present work the frequency dependence of the resonances observed is experimentally investigated in the external magnetic field, and their numerical simulation is conducted. Researches showed the qualitative agreement between the chosen model of sound interaction with magnetic system and numeral simulation. The phenomenon revealed is of interest from the viewpoint of its applications in spintronics, acousto-optics and acousto-electronics.
CHARACTERISTICS OF ALINN GRADED-GAP GUNN DIODES
M. V. Kaydash
Semiconductor nitrides are promising materials for high-speed solid-state electronic devices, including those based on the intervalley electron transfer effect. However, due to various reasons, for instance, high power consumption and difficulties of heat removing out of the device active region, the research literature contains no information on the experimental generation of electromagnetic oscillations by means of Gunn diodes based on GaN or InN. The paper presents the following results: firstly, we have proposed the idea how to reduce power consumption and to increase the Gunn diodes efficiency; secondly, we have carried out the numerical experiments on the generation of oscillations by means of Gunn diodes based on graded-gap AlInN, and thirdly, we have optimized the parameters and got the output characteristics of diodes with different cathode contacts in a wide range of frequencies. We have analyzed both harmonic and biharmonic operating modes of the diodes. We have found out that graded-gap AlInN Gunn diodes outperform InN- and AlN-diodes of the same type by generation efficiency, output power and cutoff operating frequency which equaled 0.9 ¸ 1.3 THz at the active region length of 0.15 mm. Power consumption of graded-gap AlInN-diodes is 3 ¸ 20 % less than power consumption of InN-diodes. Results of our study extend the knowledge of the physical processes of charge transport in complex semiconductor structures and can be useful for the development of new high-speed devices based on semiconductor nitrides.
G. À. Alexeev, L.V. Stulova
The review deals with studying of features of the collective interaction between distributed electron bunches and the orthogonal field component of the traveling wave spatial harmonic under the short-time interaction between singular electrons and this harmonic. It is shown that under condition of synchronism between the velocity of the movement of the short-time interaction area and the phase velocity of the harmonic, the coherent collective interaction efficiency is maximum. Qualitatively, this mode corresponds to the relay race interaction between the distributed bunch and the traveling wave harmonic of HF-field. The problem relevance is provided by the necessity of the search of new interaction mechanisms, and of the design of new vacuum SHF-oscillators. We conclude that devices with the collective relay race interaction between the distributed bunches and the traveling wave of the electrodynamic system can be developed.
V. G. Kurin
Extending the range of continuous frequency tuning of oscillators, including the diffraction radiation oscillators, is an important scientific and practical problem. In the studied oscillators extension of continuous generation range is achieved by the combined (electronic + mechanical) frequency tuning. However, to date the physical phenomena accompanying the process of combined frequency tuning have not been studied in detail. A detailed experimental study of the behavior of the output power level of the oscillator showed that the process of combined frequency tuning was accompanied by crossing of adjacent resonance areas (resonances) of the oscillator electrodynamic system. In the crossing range the phenomenon of constructive interference is observed regularly (almost periodically), which reveals itself in the form of implementation of peak of output power level in the areas of combined adjustment. Thus, the effects of resonances crossing in the electrodynamic system of the test oscillator can not only continuously tune the oscillator in a wide frequency range, but also significantly increase the level of output power.
A. Ya. Kirichenko, G. V. Golubnichaya, I. G. Maximchuk, V. B. Yurchenko
In spite of widely studied electrodynamic properties of dielectric resonators, nowadays there is no information about Q-factors of laminar resonators, a kind of quasioptical dielectric resonators assembled as a set of coaxial disk laminae with certain inter-lamina spacings. The lack of the data prevents us from using the resonators for measuring electric characteristics of surrounding substances which, due to the resonator design, have an enhanced coupling to the resonator. Current research is aimed at filling this gap in our knowledge. Difficulties in theoretical calculation of Q-factors of laminar resonators caused by their complicated shape force us to prefer experimental methods in our research. In this work, Q-factors and excitation efficiency of laminar resonators are measured for the first time as functions of the number of laminae in use and of inter-lamina spacings. A minimum number of laminae needed for the excitation and an optimal spacing for supplying a maximum Q-factor have been found. The research has been carried out for resonators of large azimuthal index (n ~ 50 for the fused quartz disks) and of lower one (n < 20 for the alumina disks). It is shown that in both cases Q-factors of laminar resonators are about ten times lower if compared to the ordinary disk resonators of the same size and material, which remain uniform in the axial direction and do not contain inter-lamina spacings.
V. I. Bezborodov, V. K. Kiseliov, O. S. Kosiak, Ye. M. Kuleshov, P. K. Nesterov, M. S. Yanovsky
Widespread use of carbon composites in modern aircraft required the development of methods of non-destructive monitoring of the surface and determines the presence of moisture and heat damage, affecting the quality of adhesive joints. Applicable in the terahertz range of wavelengths for this purpose conventional reflection methods give very low contrast signals reflected from clean and contaminated samples. This paper presents a method of the internal reflection reflectometry for oblique irradiation of the surface carbon fiber with quasioptical (QO) beam at different angles through the prism of internal reflection, which are located near the surface of the sample. For realization of the method a QO-measuring installation executed on the basis of the hollow dielectric beam waveguide and a complex of the beam waveguide devices and components of the THz range was developed. Research of samples of composite materials was conducted, it showed a considerable increase of a contrast at detection of a pollution. After technical completion the reflectometer can be used in practice.