DOUBLE SCREEN SYSTEM WITH CIRCULAR UNDER-CUTTOF HOLES AS QUASIOPTICAL POLARIZER
А. О. Perov, А. A. Kirilenko, V. N. Derkach, A. N. Salogub
The polarization plane rotation generally occurs in structures having optical activity, Faraday effect or in liquid crystals. Recently, investigations aimed at creation of artificial environments (metamaterials) with similar properties have been actively carried out. The paper shows that the double screen system with circular holes can rotate polarization plane of incident plane wave, if its periodic cells have the special spatial symmetry. Theoretical and experimental results for fishnet metamaterial based on it are presented. Explanation of the phenomenon is carried out using the method of generalized scattering matrices and taking into account characteristics of the eigenfield spatial distributions, which are specified by the screen system symmetry. It is shown that there are several spatial types of the eigenoscillations, which are responsible for polarization plane rotation under plane wave excitation. Numerical experiments show that the polarization plane rotation can be controlled by changing the structure of the periodic cell, and the polarization plane rotation through specified angles can be achieved even at small distances between screens.
Q-FACTOR MEASUREMENTS UNDER CONDITIONS OF CLOSE-FREQUENCY MODES CONVERGENCE IN OPEN RESONATORS
V. N. Skresanov, V. V. Glamazdin
A method is proposed for measuring the Q-factor of microwave resonators, which allows the study of microwave properties of materials and environments using open resonators of different types under conditions of availability of close-frequency modes in the surroundings of the given mode, the radiation losses of coupling elements and crosstalk between them. Measurement of the loaded Q-factor is based on both the representation of the frequency dependence of the resonator complex reflection or transmission coefficients by the sum of fractional-linear complex functions, describing the responses of individual modes, and approximation of a square measured frequency response by means of the variation gradient method. The eigen Q-factor calculation method is based on calculation of the resonator impedance on the measured reflectance modulus. The developed algorithms for processing measurement data are implemented in a computer program and are illustrated by the example of the processing frequency dependences of S-parameters for the open dielectric mirror resonator excited with whispering gallery modes, when the S-parameters are calculated by finite element method. Measuring quality factors by the proposed method eliminates the systematic measurement error associated with the distortion of the resonance curves, and makes it possible to perform measurements in conditions where classical methods are unsuitable.
SCHUMANN RESONANCES FOR CONDUCTIVITY PROFILE OF ATMOSPHERE WITH SINGLE BENDING
Yu. P. Galuk, A. P. Nickolaenko, M. Hayakawa
Investigations of link between parameters of global electromagnetic (Schumann) resonance and characteristics of vertical profile of atmospheric conductivity remain an actual problem. We use a rigorous solution of the electrodynamic problem in the spherical Earth-ionosphere cavity by the full wave technique and compare the results with the knee model, as introduced in the literature. The vertical conductivity profile of the atmosphere was constructed by using parameters of this model, and this allowed us to build the rigorous electromagnetic solution, and to compute the energy spectra of the vertical and horizontal electric magnetic fields corresponding to the uniform distribution of the global thunderstorms over the planet. It is shown that the knee model, discussed in the literature, does not match the rigorous full wave solution and the subsequent computations of the power spectra of Schumann resonance.
VERTICAL PROFILE OF ATMOSPHERIC CONDUCTIVITY CORRESPONDING TO SCHUMANN RESONANCE PARAMETERS
A. P. Nickolaenko, Yu. P. Galuk, M. Hayakawa
Constructing a realistic vertical conductivity profile of atmosphere remains an update task for the direct electromagnetic modeling of global electromagnetic (Schumann) resonance. The conductivity data are obligatory when accounting for influence of various factors on the ionosphere: the space weather or the seismic activity. The knowledge of the regular profile is of particular importance, as it must provide in computations the actually observed values of Schumann resonance parameters in undisturbed conditions. Using the classical data, we suggested a new height profile of atmospheric conductivity in the range from 2 to 98 km, which allows obtaining the Schumann resonance parameters consistent with observations. Using the method of the full wave solution, we computed the extremely low frequency (ELF) propagation constant that corresponds to this profile of atmospheric conductivity. The high correspondence of the results obtained to the standard radio propagation model based on the Schumann resonance data is demonstrated. The conductivity profiles are also suggested for ambient day and ambient night conditions. Using the full wave solution, we computed the relevant propagation constants. The power spectra of Schumann resonance in the vertical component of the electric field were computed and compared for the globally uniform distribution of thunderstorms in the framework of standard model and different conductivity profiles. Reciprocity of data obtained to the measurements of ELF radio transmissions is demonstrated.
REMOTE SENSING OF SNOWFALLS. REVIEW
G. Veselovska
Snow is the most common type of solid precipitation, therefore the development of remote sensing methods for studying the characteristics of snow by solving the inverse problems based on a detailed study of properties of such phenomena is of a considerable interest. In general, the calculating problem of reflection characteristics for nonspherical particles of precipitation has a long history, but researches of inverse radar scattering of liquid precipitation are characterized by the most completeness. The review of mechanical and electrical properties of snow was performed and the characteristics of physical and numerical modeling of the radar scattering characteristics for precipitation particles are analyzed. The paper shows the feasibility of studying the radar scattering characteristics of precipitation particles and it the advantages and disadvantages of the modern calculation methods of radar scattering characteristics for dielectric objects were analyzed. Remote measurement of integral characteristics of snowfalls over large areas allows determining the reservation of water for agriculture, as well as components of the hydrological forecasts and providing avalanche safety in mountainous areas.
A. E. Kogut, R. S. Dolia, S. O. Nosatiuk, He Jaochan
The spectral and energy characteristics of the shielded halfspherical resonator at the forced oscillations mode are investigated experimentally at using of the slot-line. It is shown that the use of slot-line allows maximally rarefying the spectrum of forced oscillations of the shielded resonators with an exceptional allocation of whispering gallery modes and achieving the greatest Q-factor. The experimental investigation and computer simulation show that the slot-line is a channel waveguide having the resonance properties.
A. A. Barannik, S. A. Vitusevich, I. A. Protsenko, M. S. Kharchenko, N. T. Cherpak
While using whispering gallery modes dielectric resonators as measurement cells for finding the electrophysical parameters of materials it is necessary to choose the resonator structure, which is characterized by the acceptable radiation Q-factor values. Calculation of radiation Q-factor by analytical methods is possible for simple symmetric structures only. The numerical study of different shape resonators made of leucosapphire, which are limited with conducting end plates and without them are carried out in Ka-band. The disk resonators with one conducting end plate are studied experimentally too. The influence of tested material brought in the electromagnetic field on the resonator field distribution, frequency and radiation Q-factor is shown. The application opportunity of measurement cells based on such resonators for determination of (super)conductor microwave impedance and permittivity of dielectric liquids is analyzed. The obtained results make it possible to choose the resonator measurement cell with negligible radiation loss.
A. S. Vakula
Magnetic nanoparticles are used extensively in various areas of science and technology due to ability to vary their parameters over a wide range. Magnetic properties of the nanoparticles depend strongly on technique of synthesis. The impact of various techniques of synthesis on the magnetic properties of the nanoparticle is not studied well now. Therefore, in this paper the microwave magnetic properties of the Fe3O4 nanoparticles prepared by various techniques of chemical synthesis are under research. The magnetic properties are studied by the ferromagnetic resonance technique at T = 77…300 K. It is shown that the resonant frequency increases when the diameter of nanoparticle rises. The diameter depends in turn on the technique of synthesis. Also it is shown that when the temperature increases the resonant frequency and linewidth are decreased. The results of investigation can be used to select an optimal technique of synthesis of Fe3O4 nanoparticles with specified magnetic properties.
O. V. Botsula, К. H. Prykhodko
The sources of noise in the microwave and mm-cm bands with high noise power spectral density have a number of important applications, including communications, automotive location and radiomeasurement. However, there is not many efficient solid-state generators of noise at frequencies above 40 GHz. The proposed active element for noise generating (heterostructure-based diodes with the cathode static domain) may be one of them. In these paper the static, impedance and noise characteristics of the GaAs–AlGaAs and AlGaAs–GaAs-based structures were investigated. In this structures the static domain of the strong field is formed due to doping profile at the heterojunction. The characteristics of considered diodes are compared to those of similar GaAs-based devices. The existence of regions in diodes with negative resistance at frequencies close to 50 GHz was shown. The GaAs–AlGaAs-based heterostructure has the best performance for a noise generation in the frequency range of 25…75 GHz. The main properties of proposed structures are determined and can be used for further detailed analysis of physical processes of the structures and manufacturing.
O. V. Zemlyaniy
Application of chaotic signals in modern radar and telecommunications is an actual task that can significantly extend the functionality of these systems and improve their performance. In this paper, a method for information transmission using chaotic signal generated by nonlinear dynamical system with delayed feedback of ring type has been suggested. Modulating information sequence controls the parameter of non-linear element, so that it switches the chaotic modes and changes the spectral structure of the signal transmitted to the communication channel. A non-coherent reception was used for demodulation of the received message. The effectiveness of this method of information transmission for the covert operation of communication system in a complex interference environment has been shown.
S. S. Melnyk, O. V. Usatenko
The problem of designing various radio devices, such as filters, delay lines, random antennas with a given radiation pattern and so on, requires the development of methods for constructing random sequences of the parameters of these systems having specified correlation properties. An adequate mathematical approach for solving such problems is the Markov chains of higher orders. Statistical characteristics of these objects are completely determined by their conditional probability function that, in general, can be very complicated. The purpose of this paper is to present the decomposition procedure for the conditional probability function of random sequences with long-range correlationtions in a form convenient for their numerical generation. Here we restrict ourselves to the case of the state space of the system of such kind, when random values of its elements belong to the finite abstract set. The developed theory opens the way to build a more consistent and nuanced approach for the description of systems with long-range correlations. In the limiting case of weak (by value, but not the distance) correlations memory function is uniquely expressed in terms of higher-order correlation functions, allowing us to generate a random sequence with a given long-range correlations. As an example of the analytical results obtained, which can be used in practical applications, we present an example of the numerical realization of the method of construction of random sequence with specified correlators of the second and third orders.
I. P. Storozhenko
The use of variband semiconductors in uniformly doped devices with the effect of intervalley electron transfer can lead to the appearance of a static electric domain. The interest in the static domain is due to the possibility of creating a local electric field sufficient for impact ionization of zone area. Diodes with avalanche ionization in the static domain can be used as active elements of noise generators. The article analyzes the process of formation of a static domain and avalanche multiplication of current in it on the basis of the two-temperature model variband AlGaAs. It is shown that for the formation of a static domain at room temperature, it is necessary that the minimum value of the energy gap between the G-valley and the closest by energy side valley was smaller than the thermal energy of the electrons at the rate of change of the energy gap to coordinate more than 150 eV×cm–1. Accordingly, in devices based on Al0.36Ga0.64As–GaAs cathode static domain is formed, and on the basis of GaAs–Al0.36Ga0.64As anode static domain is formed. The variband semiconductor compounds in which it is possible to form a static domain were determined. Using variband compounds Al0.36Ga0.64As–GaAs with low levels of doping in the vicinity of the cathode increases the effective and integral current multipliers as compared to GaAs-diode. The findings expand the knowledge of the physical processes of charge transport in complex semiconductor structures. They can be used for technological development of new high-speed devices, such as transistors, Gunn diodes, diodes with a stationary domain, avalanche-transit diodes, frequency multipliers.
D. Yu. Кulik, L. P. Mospan, A. O. Perov, N. G. Kolmakova
The requirement of being compact is obvious for the designs of modern communication systems of civil and military purposes. The ultimate performances of perspective compact polarization rotators are examined in the paper. The rotators are formed by the dihedral symmetry structures. The dihedral structures are based on the multi-aperture diaphragms with the rectangular slots. Muti-parameter optimization is used to achieve the ultimate performances in different frequency ranges. The limits for the rotators’ application area are established. The designs, providing polarization plane rotation for arbitrary rotation angle at the acceptable values of the reflection coefficient over the frequency band are proposed. The designs make the elemental base of the receiving and the transmitting equipment broader and they are intended to provide given phase separations of the radio signals, to perform required phase correction or polarization compensation.