SPECTRAL PROBLEMS IN THE THEORY OF DIFFRACTION OF WAVES ON LAYERED MEDIA
A. V. Brovenko, P. N. Melezhik, A. E. Poedinchuk
Investigation of diffraction characteristics of layered media is due to their widespread use. However, so far in the scientific literature there is a small amount of special dependences of the layer material parameters on the spatial coordinates, when it is possible to obtain analytical solutions describing wave processes occurring in them. Most of these solutions are built with the help of asymptotic and direct numerical methods. In this paper the so-called Riccati method was applied to construct the solutions of the spectral problem for the inhomogeneous magnetodielectric layer. As a result a computationally stable algorithm for solving eigenvalue problems was obtained. The algorithm allowed to investigate resonance effects accompanying the interaction of waves with layered media, and to describe by the natural frequencies and natural vibrations the well-known concepts as the band gap in the theory of wave propagation in periodic structures and resonance in the gap in violation of the periodicity of the tangible medium parameters. The results of the research allow to study wave propagation in inhomogeneous magnetodielectric, heterogeneous Plasma and other layers of this type without significant restrictions on their physical parameters and can be used in solving inverse problems of electrodynamics, as well as in holography, tomography, radar, etc.
EIGENOSCILLATIONS AND RESONANCE PROPERTIES OF ONE-DIMENSIONAL METAL BAR GRATINGS. PART II. COMPOUND GRATING
А. О. Perov, А. А. Kirilenko, S. L. Senkevich
At the present time, perforated metal gratings are experiencing a new wave of interest to their resonant properties, caused by the study, interpretation, and possible practical use of the «enhanced transmission phenomena». This work goal is the analysis of the one-dimensional periodic grating properties based on the V. P. Shestopalov school works, i.e. the study the oscillation spectra, the spectra formation principles, defined, in particular, by the structure of the grating period, and then the analysis of the spectra impact on the resonance characteristics. H-wave scattering peculiarities on 1-D metal compound grating are considered. Resonant behavior treatment is based on open periodical resonator spectral theory. The lower eigenoscillations of such multi-element structures are investigated, which are responsible for the resonant behavior when various defects for the multiperiodical cell are realized. The relation between scattering characteristics and compound grating spectra is shown. On this basis, one estimates the resonance amount depending on the cell topology and geometry, and also one gives a new interpretation of "phase" resonances. Resonance behavior of grating is described from a unified standpoint of spectral theory, which allows not only to determine the relationship between different resonant phenomena, but also to determine the root cause of such behavior caused by the excitation of certain oscillations.
RESONANT MATCHING OF DUBBED PERIODICAL STRUCTURE IN DIFFRACTION RADIATION OSCILLATOR
V. S. Miroshnichenko, M. Yu. Demchenko, Ye. B. Senkevich
Diffraction radiation oscillators, in which open resonant systems are used, are the perspective middle-power sources for short millimeter waves and terahertz frequencies. When working wavelength is shortened, it is necessary to find a new type of resonant systems with enhanced efficiency of energy change between electron beam and resonant field for such oscillators. The second problem is the highness of spectrum density in open resonant system by shortening of wavelength. One way to overcome such difficulties is the use of resonant matching of dubbed periodical structure instead of phase matching in open resonant system of oscillator which is followed by the more sufficient changing of resonant field. The results of electromagnetic modeling of open resonant system for diffraction radiation oscillator with resonant matching dubbed periodical structure by the use of resonant step heterogeneity in the form of a rectangle groove on the mirror are presented. It is shown that the use of resonant matching of dubbed periodical structure and resonant field in open resonator allow us to rarefy the spectrum of excited modes and to increase the coefficient of resonant field using by the electron beam. The properties of two open resonant systems with traditional phase matching and resonant matching of dubbed periodical structure for 5-mm waveband are presented. The investigations allow us to increase the efficiency of diffraction radiation oscillators for short millimeter waves and to overcome difficulties by using such oscillators in terahertz frequencies.
THE FEATURES OF RADIATION FORMATION BY THE SMALL APERTURE SHF ANTENNAS
I. V. Ivanchenko, N. А. Popenko, V. I. Pishchikov, М. М. Khruslov, R. E. Chernobrovkin
Currently, one of the major problems is to create the broadband individual small aperture radiators and antenna arrays for wireless local area networks, nondestructive problems, the environment monitoring, biology, medicine, etc. Under conditions when the radiator size is comparable to the operating wavelength, the increasing mutual influence of the individual antenna elements and the increasing role of edge effects in the formation of antenna radiation become principal and require separate and detailed studying. In the paper the approach involving the analysis of near-field distributions of the concrete individual radiator is realized to explain the features of the radiation formation in the antenna array and planar spiral antenna. The near-field distributions are measured and their analysis is carried out along with the electromagnetic field distributions measured in the far field region. The special waveguide probes are used. It is shown that relative to the antenna array the electromagnetic waves scattered at the edges of array elements and at the ground plane cause the field intensity oscillations in the main lobe of the radiation pattern and the increase of the cross-component level. As regards the spiral antenna, the differences in the near-field distributions for the orthogonal components lead to a difference in the suitable radiation patterns and to the irregular changes of the axial ratio in the operational frequency band. The proposed approach to the analysis of antenna performance, as well as the presented and tested antennas can be used in designing different wireless communication systems.
RESONANCE PROPERTIES OF PLANAR METAMATERIAL FORMED BY ARRAY OF ROSETTES ON UNMAGNETIZED FERRODIELECTRIC SUBSTRATE
S. Yu. Polevoy, S. L. Prosvirnin, S. I. Tarapov
Chiral structures are of a great interest both for fundamental physics, where they can be successfully used to model the propagation of electromagnetic waves and elementary excitations in condensed media (from crystalline to amorphous), as well as from the application point of view. Such structures can be very promising for the design of compact magnetically controlled microwave devices. However, in the millimeter wavelength range, which is today one of the most important in the application point of view, the amount of experimental research of plane chiral structures is insufficient. In this paper the electromagnetic resonance properties of the planar metamaterial, formed by array of metallic plane chiral rosettes located on unmagnetized ferrite substrate are investigated. The experimental and calculated frequency dependences of the transmission coefficient for several values of the structure period are obtained. The dependence of the resonant peak frequency of the transmission coefficient on the structure period is analyzed. The joint analysis of the experimental and theoretical data is carried out. The research results can be applied in telecommunications, high-frequency technology (the design of filters, polarizers, directional couplers) and antenna design.
ULF MAGNETIC FIELD DEPRESSION AS A POSSIBLE PRECURSOR TO THE 2011/3.11 JAPAN EARTHQUAKE
A. Schekotov, E. Fedorov, Y. Hobara, M. Hayakawa
The depression (reduction in amplitude) of ULF magnetic field variations of magnetospheric origin is studied at various distances from the epicenter of the strongest earthquake (EQ), which occurred in Japan on March 11, 2011. For this purpose, we have used the ULF data in Japan recorded by fluxgate magnetometers at three places located at distances of ~300 km to ~1300 km from the epicenter of the main shock. The period of data analysis is from December 1, 2010 to May 31, 2011. We have found a sharp depression of the horizontal ULF magnetic field component at the frequency of 0.03…0.05 Hz (30…50 mHz) at all of three Japanese observatories (Kakioka, Memambetsu and Kanoya) three days before the first strong foreshock (Mw = 7.5) and five days before the main shock (Mw = 9). This maximum depression is found to be several times greater than all previous deviations, but the depression seems to be most enhanced at Kakioka, the station nearest to the EQ epicenter. So that it is likely that this phenomenon could be a possible precursor to the huge 3.11 EQ.
THE CHOICE OF ROOT-MUSIC PARAMETERS FOR RADAR MEASUREMENTS OF TARGET ELEVATION ANGLES NEAR SEA SURFACE
Yu. A. Pedenko
The method of spectral resolution root-MUSIC has been considered recently as one of the means to solve the problem of increasing the accuracy of measuring the elevation of low-altitude targets above rough sea. However, the traditional approach to the selection of a priori parameters of the method developed with spectral analysis does not reveal its advantage in accuracy compared to the best special methods proposed to solve this problem. This was the reason for the development of various modifications of the method. In this paper, computer simulations are used to study the method in its classical form, but with use of a priori parameters, including significantly different from those used in other studies. In particular this applies to the signals subspace. It was found that the increase the signal subspace dimension from two, due to the use of a specular reflection model, up to five-seven, improves the measurement accuracy of the elevation of low-altitude targets several times. It was found that increases in accuracy occur in any case of strong diffuse or strong specular reflection of radio waves from the sea.
ATMOSPHERE MONITORING OVER THE KHARKOV REGION BY MEANS OF GNSS
A. L. Kovorotniy, Yu. V. Goncharenko, V. N. Gorobets, F. V. Kivva, A. I. Gorb, A. Yu. Balan
The state of the atmosphere rating, weather and climate forecasting were actual for other areas of science and engineering. This paper deals with the development of methods for determining the tropospheric zenith delay (ZTD) from remote sensing data using GPS systems and algorithm of the experimental validation. The raw data were obtained by means of a regional system of high-precision satellite geodetic measurements in the Kharkiv region (NGCNET). Later they were used to calculate the zenith delay and weather parameters in each of the receiving points. The article describes a method’s for determining the hydrostatic and “wet” (ZWD) component of the tropospheric delay on the data obtained by the two-frequency receivers GPS. A comparison between the data calculated from the known models, and received from NGCNET. It is shown that the correlation coefficients between the values of the “wet” ingredients tropospheric delay is 0,5–0,6 for summer season and 0,7–0,8 for winter and spring seasons measurements. The correlation radius of ZWD values for different seasons were evaluated in this work.
ANOMALOUS TRANSPARENCY OF PERIODICALLY MODULATED SLABS OF LAYERED SUPERCONDUCTORS FOR TERAHERTZ RADIATION
D. V. Kadygrob, N. M. Makarov, F. Perez-Rodriguez, T. M. Slipchenko, O. I. Lubimov, V. A. Yampol'skii
We predict the enhanced transmissivity of modulated slabs of layered superconductors for terahertz radiation due to the diffraction of the incident wave and the resonance excitation of the eigenmodes. The electromagnetic field is transferred from the irradiated side of a slab of layered superconductor to the other one by excited waveguide modes which do not decay deep into the slab, contrary to metals, where the enhanced light transmission is caused by the excitation of the evanescent surface waves. We show that a series of resonance peaks can be observed in the dependence of the transmittance on the varying incidence angle, when the dispersion curve of the diffracted wave crosses successive dispersion curves for the WGMs. We also consider the opposite effect when the transparency of a modulated thin slab (with a thickness much less than the skin depth) is significantly reduced due to the resonant excitation of the eigenmodes.
EXPERIMENTAL RESEARCH OF THE DUAL-FREQUENCY MODES IN DIFFRACTION RADIATION OSCILLATOR
V. G. Kurin
Currently, multi-frequency signals are applied in multi-channel communication systems and multi-frequency RLS. The use of multi-frequency radar systems increase the efficiency of detection, recognition and distinction of objects, which significantly improves the accuracy of determining the coordinates of group goals and plays a significant role in the development of intelligent radar systems for automatic object identification. For the radar image formation the range and the frequency spacing of the shaper (oscillator) of the probing signals are of equal importance. Frequency spacing supports to the radar images shape that are similar in visual perception and accustomed to humans. In the tested oscillator frequency spacing can be adjusted by changing the anode voltage, which is undoubtedly one of the conditions causing the high-performance of dual-frequency millimeter-wave radar. The task of the oscillator excitation in the two frequencies is solved by changing the conditions for the simultaneous excitation of the oscillator in two modes, namely, the diffraction radiation mode, and the so-called leddertron mode. In both of these modes energy from the open resonator can be displayed on the fast (“volume”) waves through the aperture coupling, made in one of the mirrors (“top”) of the open resonator. It turned out that the specified modes in the oscillator at different frequencies are excited when in open resonator the resonant mode is excited, which forms two opposite-field spot in the space interaction (in the direction of the electron beam). In this case, the electron beam is converted from a single thread in the two-line, which results in stable operation of the oscillator at the two frequencies. The experimental results show the stability and efficiency of the oscillator at the same time in these modes. Moreover, the spacing generated frequencies can be changed by varying the anode voltage. Research results extend the functionality of the oscillators in the various fields of science and technology. In particular, it is interesting to investigate the possibility (or impossibility) of matching the frequency of these modes.
A. A. Gurko, K. I. Suchkov
At present there are no techniques of forecasting the cathode durability and its working capacity at the lowered ambient temperature, and the conclusion about meeting technical specifications requirements on these parameters is estimated only by results of control party natural tests. In the scientific literature there is no uniform point of view on the ways to define the emissive ability of cathode material for devices with the crossed fields. There are great difficulties in substantiation of the cathode parameters choice for each concrete device. Research of various parties of Pd-Ba material applied in cathodes of serial magnetron is executed. The condition of autoemission transition to explosive by a magnetron working capacity estimation is checked at the pulse duty factor essentially below the technical specifications requirements. By means of the research results the conclusion about correlation between magnetron durability and its working capacity at the lowered temperature is drawn. As a criterion the experimentally defined pulse duty factor is offered, at which the operating conditions establishment in normal climatic conditions is realized at the first magnetron inclusion. The received technique allows to carry out 100 % forecasting of performance of the technical specifications requirements on durability. It is similarl to a check technique on frost resistance, but under normal climatic conditions.
A. A. Omirov
Among all the competing oscillation modes in coaxial magnetron (CM) the slot oscillation mode causes the greatest difficulties. Application of its effective reactive suppression allows to raise magnetron efficiency at the expense of easing active suppression. Available in scientific literature, the methods for a slot oscillation mode parameters calculation contain errors and are incorrect in case of applying a peripheral wall of anode slowing down system (ASS) more than 0.1l. Also there are no researches on application of a slot oscillation mode reactive suppression in a mm wavelengths range CM. The existing method of parameters calculation of a slot oscillation mode has been corrected. The calculation update and also a new method have been suggested for the use of ASS with peripheral wall thickness more than 0.1l. The way of slot oscillation mode reactive suppression in a mm wavelengths range CM by manufacturing of two group of a rectangular profile slots with various axial extent has been suggested. “Destruction” of a spatial harmonics spectrum and the HF-field structure of a slot oscillation mode is considered at reactive suppression application. The research has shown that at grouping of a rectangular profile slot with various axial extent in a mm wavelengths range CM the achievement of reactive “destruction” of slot oscillation mode is possible at least not worse than in a cm wavelengths range at various profile slot application. Researches results expand knowledge about reactive suppression of a slot oscillation mode in CM and can be applied by working out and improvement of parameters CM including mm wavelengths range.
E. D. Prohorov, O. V. Botsula, O. A. Reutyna
Currently, the devices that can operate in the millimeter and submillimeter ranges are actively investigated. For the development of this range solid-state generators are used, operating at frequencies of 100…150 GHz, with further multiplication by frequency multipliers of these relatively low frequencies up to the required level (in fact, so far to 1…2 THz). Semiconductor devices that can be used as oscillators and amplifiers have been proposed previously. It is a diode with a negative differential conductivity, which is due to the lateral tunnel or resonant-tunneling boundaries. In this study electronic processes in diodes with a resonant tunneling boundary based on GaAs are considered, provided that the resonant tunneling is limited by the length of the boundary. Dependences of the active and reactive components of the impedance of a planar diode with resonant tunneling boundaries for the real diode parameters are determined. It is shown that the frequency possibilities of the diode with resonant tunneling boundaries depend strongly on the location of the boundary. It is shown that the efficiency of generation and the frequency range are reduced by moving the resonant-tunneling boundary to the anode.
I. N. Bondarenko, A. V. Galich, S. I. Troitski
For non-contact microwave diagnostics of materials and media at scanning microwave microscopy cavity transmitters with coaxial microprobe are widely used. Measurement sensitivity is then determined by quality factor of the cavity of the meter and the efficiency of its coupling with the probe. The aim of our investigation is to analyze the conditions of excitation and maintenance of high-Q oscillations in irregular hybrid structures as coaxial cone, a truncated cone, connected to a coaxial cone, cylinder volume, coupled with a truncated cone and coaxial cone. Numerical model simulation and experimental device examination define the conditions of excitation and types of high-Q oscillations in such irregular hybrid structures and the conditions for communication of high-Q oscillations with an aperture of a coaxial probe parts are also identified. Irregular hybrid structures in configurations discussed in the paper can be effectively used to create high-Q resonator transducers for contactless microwave diagnostics of different objects.