STUDY OF SPECTRAL AND POLARIZATION CHARACTERISTICS OF LAYERED CHIRAL MEDIA
N. N. Beletskii, S. Y. Polevoy, S. I. Tarapov
Study of layered chiral media is interesting both for fundamental and applied physics. Such media may be used for design of microwave devices such as filters and polarizers. Despite the fact that the spectral and polarization characteristics of the layered media are studied well enough now, the layered chiral media are studied insufficiently. In this paper we study the spectral and polarization characteristics of layered chiral media using the propagation matrix method. The coefficients of the propagation matrix of the periodically layered chiral medium are obtained. The transmission and reflection coefficients of linearly polarized electromagnetic waves for the structure consisting of planar chiral layers were calculated. The boundaries of the forbidden bands for a periodic medium, which unit cell consists of two different chiral layers were determined. It is shown that the boundaries of the forbidden bands do not depend on the chirality parameter of the layers of the structure. It was found that for certain values of the layers thicknesses, the forbidden bands width tends to zero. It is found that the proposed calculating method for the reflection and transmission coefficients can be used to determine the effective constitutive parameters of artificial chiral metamaterials.
INCREASING A CIRCULAR ANTENNA ARRAY DIRECTIVITY
M. V. Balaban, A. V. Somov
Recently, circular antenna arrays consisting of one or more rings of similar sources attract more attention. This is due to the possibility of using such arrays for producing powerful transmitters. This paper presents the study of radiation properties of a circular antenna array with linear polarization based on one or several rings of similar sources. As a single source we consider simple or complex Huygens elements. We present the results which show the influence of the antenna radius, number of elements and single elements directivity on the radiation pattern of the system. The possibility to increase the directivity of the system while increasing the number of circles in the array is shown. Finally, we present an example of modeling of radar system based on four-circular antenna array with high directivity and low level of sidelobes.
ANALYSIS OF THE WIDE-BAND PROPERTIES OF BICONE FORMED BY THE FINITE AND SEMI-INFINITE SHOULDERS
O. M. Sharabura
Bicone is the basic structure for study of the electro-dynamic properties of vibrators, monopoles and biconical antennas. The approximate methods are usually applied for analysis of these structures. Here, the electrodynamic characteristics of the metallic bicone formed by the finite and semi-infinite cones with arbitrary values of angular parameters and the length of the shoulder. The field distribution in the vicinity of the edge, the frequency dependence of the main mode magnitudes and the far-field patterns for a number of the bicone configurations are investigated. The results may be used for numerical analysis of the biconical antenna parameters.
RETRIEVAL OF LIQUID PRECIPITATION INTENSITY BY MULTIFREQUENCY ACTIVE-PASSIVE REMOTE SENSING
A. M. Linkova, G. I. Khlopov
Development of methods for remote sensing of liquid precipitation is quite an actual task for both practical application in different areas of agriculture and solution of theoretical tasks of atmosphere physics. The method of retrieving the intensity of liquid precipitation by active-passive sensing based on double frequency radar and radiometer is considered. The expressions for active-passive sensing of rains are obtained in the form of system of three integral equations. The algorithm for solution of inverse problem by numerical methods is proposed, which is based on the database of received powers of double frequency radar and radiometer brightness temperature calculated by solving the direct problem of active- passive sensing for different values of drop size distribution parameters. Numerical simulation of active-passive remote sensing of liquid precipitation at the range of intensity up to 30 mm/h and radar wavelengths 8.2 mm and 3.2 cm, and 3.4 cm for radiometer has been carried out. It was shown that the proposed algorithm can retrieve the rain intensity with error not more than 10 %.
RADAR CROSS SECTION OF NONSPHERICAL RAINDROPS
G. Veselovska, G. Khlopov
Considerable attention is devoted to radar methods of measuring characteristics of rains in connection with studies of physical processes in the atmosphere, as well as for solving practical problems. However, existing methods of calculating the reflection characteristics are based on the assumption of a spherical shape of rain particles, whereas, the shape of real raindrops in most cases has a nonspherical shape. Therefore, in this paper, the research results of backscattering are considered from ellipsoidal drops and Pruppacher-Pitter drops that are most widely used at description of nonspherical particles. In the process as a method of calculation we use the dipole scattering approximation and rigorous method of moments. Comparative calculations were made for horizontal and vertical polarization of the incident field at wavelengths l = 0.8, 3.2, 5.5 and 10 cm, which gave values of the calculation error of the effective radar cross section of drops using approximate methods. Also polynomial approximation of rigorous calculations results is proposed and the expansion coefficients are found, which allows to use the given data for calculation of the scattering characteristics in the case of polydisperse medium.
DETERMINATION OF TROPOSPHERE REFRACTIVE CHARACTERISTICS IN SHADOW ZONE BY DISTANT SOURCE RADIATION. PART 1. MODEL
V. B. Zamarajev, V. B. Sinitsky
The estimation of troposphere refraction using the satellites signals is the actual task because it is related to practical important problem of short-term radio waves propagation diagnostics. The paper is devoted to the development of imitating computer model for satellite’s setting in the zone of a geometrical shadow where the effects of troposphere refraction are enhanced. The model uses the numerical calculations based on the diffraction and ray optics principles. The calculations are carried out for the Earth of natural radius, because in the case with a distant source the concept of equivalent radius of the Earth is inapplicable. The results of calculations of attenuation factor in the field of the geometrical shadow, executed according to the diffraction theory for a virtual source, are transformed on the horizon of a real distant source by ray optics modeling for the layered-stratified atmosphere. The principle establishing equality of an attenuation factor on links with the common over-the-horizon site is used. Calculations of attenuation factor are executed for a set of linearly-exponential profiles of troposphere refractive index at different ground values and various gradients (from standard to almost critical refraction). The received characteristics can be used for solution of the inverse problem of refraction i.e. restoration of refractive index gradient of the troposphere surface layer. It is shown that informative parameters for estimation of refraction are the angle of radiosetting and the slope of a diffraction site of attenuation factor.
LAYERED SUPERCONDUCTORS REFLECTANCE CONTROL BY MEANS OF STATIC MAGNETIC FIELD
T. N. Rakhmanova, Z. A. Maizelis, S. S. Apostolov, V. A. Yampol’skii
High-temperature layered superconductors support propagation of electromagnetic waves of THz range, which is promising for various applications. The possibility to control wave reflectance by means of external static magnetic field has special interest, since the magnetic field is a flexible tool to customize the transparency of samples of layered superconductors. It is shown, that due to nonlinear relation between electromagnetic field and the current inside of the layered superconductor, the electromagnetic wave reflectance depends on the value of magnetic field. The presence of magnetic field can either increase or decrease the reflectance. The analytical expressions for the reflectance are obtained and its behavior when changing the parameters of the problem is analyzed. Special attention is focused on the problem of minimization of reflectance as a function of incident angle, the value of static magnetic field and wave frequency. The conditions for nearly full suppression of reflectance are found. The results can be used to construct filters, detectors and sources of the terahertz radiation.
THE INFLUENCE OF REFRACTIVE INDEX ANISOTROPY ON THE OPTICAL AND EMISSION CHARACTERISTICS OF LASER MATRICES ON THE BASIS OF THE DYE-DOPED POLYURETHANES
S. V. Nikolaev, V. V. Pozhar, M. I. Dzyubenko
Recently, an intensive growth of interest in the investigations directed at the creation of efficient solid-state dye lasers has been observed. The significant part of these studies is dedicated to synthesizing solid active media on the basis of the transparent polymers of different chemical origin. Polyurethane and its derivative substances is one of the classes of polymers that can be applied in laser technology. Compared to other kinds of polymer media the polyurethane substrates are investigated much less. In particular, this concerns their optical properties. This work is dedicated to the study of the reasons for the appearance of the anisotropy of the refractive index of polyurethane active media and its influence on the optical and emission characteristics of laser matrices. It is established that the optically anisotropic state of medium is caused both by internal stresses of polyurethane as a result of intermolecular interaction and thermal stresses induced by powerful pumping. It is shown that the optical anisotropy of media leads to the presence of local birefringence in them. The influences of the birefringence induced by transverse pumping on the polarization of the laser emission were investigated. It is established that under such conditions the polyurethane active elements generate polarized radiation even during the excitation by the nonpolarized light.
А. О. Puzanov, A. N. Kuleshov, B. P. Yefimov
The considered problem is topical because of the necessity to reduce the power consumption of the set-up intended for ignition and long-term sustaining of combustion of torch discharge (TD) in case of industrial application, and because of the complexity of TD investigations in wide frequency band. The aim is to develop the method for measuring TD resistance. In scientific literature quite complex and expensive methods of obtaining the result are described. In this paper we have obtained formulas which allow to determine TD resistance in the power range up to 1 kW according to measurements results at two frequencies of generator minimal voltages required for sustaining TD combustion. The frequency dependencies for these voltages have been obtained. Simple estimation expressions for TD parameters have been derived; their accuracy is compared in different cases. The limits of frequency band in which the obtained expressions remain true have been found. The suggested method allows to simplify the result obtaining due to the reduction of cost and complexity of the set-up. The performed work contributes to a more effective use of material and technical resources.
E. D. Prokhorov, O. V. Botsula, O. A. Reutina
The study of millimeter and submillimeter wave ranges is one of the topical tasks of radiophysics. However, there are not many active elements that can operate in the specified range. The diodes with tunnel anode (TA) and tunnel lateral boundary (TB) have been proposed. The current-voltage characteristics and generation efficiency of GaAs-based diode were investigated. The researches aim is the determination of tunnel anode and tunnel boundary parameters on a diode’s characteristics in low and higher frequencies and a frequency limit estimating. The generating ability of diodes with tunnel anode and tunnel boundary in the range from tens to hundreds of GHz and the possible existence of two voltage regions with NDC and generation have been shown. The oscillation efficiency is 10–15 % on low frequency and percent share on frequencies is more than 100 GHz. The main properties of the proposed structures are determined and can be used for further detailed analysis of the physical processes of the structures and manufacturing.
V. N. Zheltov, A. I. Tsvyk
The main problem of the modern vacuum electronics is the increase of generators power characteristics and the increase of their frequency range. The study of static sheet electron beam (EB) formation in DRO interaction space has been presented with the aid of the analytic theory. The processes of EB formation near diffraction grating has been studied while varying physical and technical parameters of DRO electron-optic system with diode gun, in particular on distance between mirrors and electron gun parameters. It is revealed that EB in DRO is different from that in classical O-type devices.
O. V. Gurin, A. V. Degtyarev, V. A. Maslov, V. A. Svich, V. S. Senyuta, A. N. Topkov
Cylindrical vector beams have many applications, including the acceleration of electrons, material processing, a high-resolution metrology, microellipsometry and spectroscopy. The results of studies of their propagation and focusing features in the terahertz range are practically absent. Theoretically on the basis of the vector theory of Rayleigh-Sommerfeld and experimentally using the radiation of the terahertz waveguide laser (l = 0.4326 mm) the study of the physical characteristics of propagation in free space of moderate and sharp focusing of radiation laser beams is conducted. These beams are excited by the modes of the dielectric resonator with circular waveguide with the different spatial polarization of the field. The obtained results are expanding the knowledge of the features of propagation in different zones of diffraction and focusing of laser beams of terahertz range.
V. Bezborodov, O. Kosiak, Ye. Kuleshov, V. Yachin
The polarization transformers, main elements of which are differential phase section (DPS) are widely used while constructing the polarization radio paths of terahertz (THz) range. Sub-millimeter waves application allows to realize researches in radio astronomy, radio spectroscopy, biology, medicine, physics of the atmosphere, etc. Due to the fact that quasi-optical transmission lines are used in the THz frequency range, the transition to optical principles of DPS construction using dielectrics exhibiting birefringence is justified. Some of crystals (sapphire, iceland spar, quartz, etc.) possess this property. In this paper, some artificial dielectric structures possessing form birefringence with a period of the structure comparable to the wavelength are considered. The classical methods of calculating such structures with a period much smaller than the wavelength are known. To solve the problem of dispersion of a plane monochromatic wave on a lattice consisting of dielectric bars without loss, we used a numerical method of integral functionals in the frequency domain for multimode dispersion problem. This method is based on three-dimensional integral equations for the equivalent electric and magnetic polarization current of periodic medium. Also the matching conditions of such structures with free space when obtaining required differential phase shift are considered. The matching is carried out by using dielectric layers. Experimental study of such DPS was carried out, the results of the study has confirmed the correctness of the choice of such structures and conditions of their matching.
S. V. Pogorelov
One of the priority directions of upgrading quantum-optics gauges is the increase of laser power and improvement of its spatial-time parameters. At the same time the problem of high-precision measurements of these parameters in the actual-use environment of laser gauges is important. The specific features of registration process appear at the measurements of high-energy laser pulse characteristics. They are caused by non-linearity behavior of interaction of powerful laser radiation with receiver material. The aim of the work is the determination of transfer function of thin-wire bolometer of laser pulse energy on wavelength 1.06 µ with regard to nonlinearity and non-uniformity of intense distribution along the receiver. The heat-balance equation has been solved with regard to derived temperature dependencies of basic physical parameters of the bolometer. The dependencies of effective temperature of bolometer heating on the effective specific energy of incident laser radiation have been determined. The inverse function has been approximated with a polynomial of the second order. This function is transfer one. Numerical values of coefficients of a cubic equation of measurements have been determined with their relative root-mean-square deviations. It allows us to carry out absolute measurements of energy parameters of laser radiation on wavelength 1.06 µ with thin-wire bolometers. Thus, the method of absolute calibration of thin-wire bolometer of laser pulse energy on wavelength 1.06 µ is substantiated.