RESONANT INCREASE OF MAGNETICAL-TYPE EIGENMODE QUALITY OF AN OPEN RESONATOR WITH A SPHERICAL DIELECTRIC INSERT
Yu. V. Svishchov
A spherical-mirror open resonator (OR) carrying different-kind discontinuities finds many applications in SHF technology. But in the case of a spherical dielectric insert, any mathematically rigorous results on OR spectral characteristics in the resonance wavelength region are not available in the literature on the subject yet. For one thing, the present paper suggests a rigorous mathematical model of axially symmetric, magnetic-type eigenoscillations of a spherical-mirror open resonator with a spherical dielectric insert. For another, upon this model, eigenfrequencies and eigenoscillastion qualities of the mentioned electromagnetic structure are studied versus its geometrical and constitutive parameters. The main result is recognition of the effect of eigenoscillation quality resonant fall (rise) under changes of geometrical and constitutive parameters of the spherical insert. Also, the nature of the resonant change of eigenoscillation quality has been understood. The obtained results should be taken into account when different type discontinuities are required to accommodate in the OR volume and, also, when the field amplitude distribution is reconstructed using the probing perturbation method.
GIANT “OPTICAL ACTIVITY” OF COMPOSITE PLANE-CHIRAL IRISES IN MICROWAVE
V. N. Derkach, A. A. Kirilenko, A. O. Perov, S. A. Prikolotin, A. M Salogub
Recently, much attention is paid to the study of metamaterials – composite artificial media with different physical properties and characteristics, which is not always possible to obtain using existing natural materials. In particular, the possibilities of using plane-chiral structures in the rotation devices of polarization plane of EM radiation are explored actively. Theoretical analysis and experimental research of the properties of two-layer composite plane-chiral irises (СPChI) in a square waveguide are presented in this paper. Experimental research have been carried out at 3cm band of electromagnetic waves. It is shown that the composite СPChI exhibits giant “optical activity”, and in accordance with the calculation results it rotates the plane of polarization by 90°. The calculated and measured maxima of the cross-polarization component of the transmission coefficient coincide in frequency with high precision and losses do not exceed 0.2 dB. The possibility of tuning bandwidth by varying the distance between the irises (layers) is demonstrated.
BEAMFORMING BY THE METALIZED DIELECTRIC DISK WITH OFF-AXIS EXCITATION
S. Rаdionov, I. Ivanchenko, N. Popenko, M. Khruslov
With reference to the small-size radiators used in different communication systems the problem of forming a narrow radiation pattern (RP) remains relevant today. A number of papers published both in domestic and foreign scientific journals are devoted to the problem like that. In this paper we implemented an approach involving the use of analysis of the electromagnetic near-field distributions to explain the features of beamforming by the small-aperture radiator with off-axis excitation. The results of simulations obtained in studying such characteristics of the proposed original dielectric disk radiator as the near-filed distribution, RP and return loss coefficient when changing the geometric parameters of radiator components allowed us to determine the optimal dimensions of those for beamforming given in advance. The prototype of the dielectric disk radiator with optimal geometric parameters was manufactured and tested. The main characteristics of the prototype are as follows: –10 dB impedance bandwidth is 20 %; beamwidth in the E-plane and H-plane is equal to 28° and 40°, respectively; the elevation angle of peak directivity is oriented towards zenith. The given approach to the analysis of the radiator performance can be used in designing new radiators with the specified characteristics. The proposed radiator seems to be very attractive with a viewpoint of its application in the wireless communication systems.
ELECTRON DENSITY AND LOWER IONOSPHERE HEIGHT ESTIMATIONS BY RESULTS OF ANALYSIS OF MULTIMODAL TWEEK-ATMOSPHERICS
Y. V. Gorishnya
Tweek-atmospherics (tweeks) are used for low ionosphere investigation together with VHF-radio station’s signals. Within the framework of existing tweek propagation models there is a projection of both decrease and increase of effective reflection height with mode index increasing. Therefore, the analysis of experimental data arouses interest and is based on improved method, which allow us to obtain the more detailed estimations of the ionosphere reflection height. For ensemble of experimental records of tweek-atmospherics (tweeks) the source ranges and effective reflection heights were determined, corresponding to Earth-ionosphere waveguide first-order modes and higher-order modes. The observable harmonic number in tweeks according to source range, local nighttime and effective ionosphere reflection height was investigated. The obtained results show the increase of effective reflection height in low ionosphere during the night. These data also demonstrate the increasing of percentage of tweeks with higher-order harmonics in case of effective ionosphere height 87…89 km. The maximum of average tweek harmonic quantity is observed in period of 20…24 hours of local time. The difference between effective reflecting height for the first and second tweek harmonics was observed, which is 1.4 km on the average. Within the framework of anisotropic ionosphere the electron density values were obtained by such measurements at altitudes of tweek reflection. The investigation results allow to select the adequate tweek propagation model and to estimate lower ionosphere parameters.
ENERGY LOSS OF CHARGED PARTICLE MOVING ALONG A SPIRAL PATH
A.V. Dormidontov, Yu. V. Prokopenko, S. I. Khankina, V. M. Yakovenko
One of the topical problems of modern radiophysics and electronics is the study of the generation mechanisms of electromagnetic waves emitted in motion of charged particles in various electromagnetic systems. It is fundamentally important that the particle energy losses per unit time in the excitation of system eigenoscillations are included to the number descriptions of possible generation process. Knowledge of the energy losses allows us to find the increments and to determine the threshold conditions of oscillation instability when charged particles move in the system. In this paper, using Maxwell's equations and based on an integrated approach (analytical and numerical) the energy losses of a charged particle moving along a spiral path over the surface of the cylinder, which is a dielectric or metal, were determined. The conditions under which there is a gyrosynchrotron radiation of electromagnetic waves in the system were stated. The research results extend and systematize knowledge (our conceptions) about generation mechanisms of electromagnetic waves in electrodynamical systems that form the basis of microwave oscillators.
VISION THROUGH TURBULENT ATMOSPHERE
Yu. V. Kornienko
The paper is dedicated to the 110-aniversary of A. Ya. Usikov. The history of scientific researches in the digital image processing at the Usikov Institute for Radiophysics and Electronics of the National Academy of Sciences of Ukraine (IRE of NASU) is briefly written. The main point of the paper is the reaching of the diffraction resolution in observations through the turbulent atmosphere and the new results obtained in the IRE.
SUBMILLIMETER DIODE ON GALLIUM ARSENIDE NANOSTRUCTURE
N. M. Goncharuk, N. F. Karushkin, V. A. Orehovskiy, V. V. Malyshko
Operating frequency of submillimeter wave range diode on AlGaN/GaN one-barrier nanostructure with nonresonant tunnelling of electrons is determined by an inertia of electron tunneling under potential barrier of the structure. With the aim to increase the operating frequency in the present work the same diode on AlGaAs/GaAs nanostructure is investigated, where effective mass and, hence, tunneling inertia of electron is less. Dependences of negative conductance and a reactance of the diode on its diameter, transit angle, frequency and tunneling time have been obtained. Optimal values of diode diameter and transit angle, which correspond to maximal negative conductance of the diode with different tunneling time, have been determined. It has been shown that operating frequency of gallium arsenide diode is one and a half more than the same of gallium nitride diode with equal parameters of a barrier layer. Maximal negative conductance of gallium arsenide diode is less than its value for gallium nitride diode with the same tunnelling time. The expediency of the investigations is confirmed by the obtained results.
S. A. Berdin, N. P. Gadetski , V. G. Korenev, A. N. Lebedenko, M. I. Marchenko, I. I. Magda, O. G. Melezhik, V. A. Soshenko, K. V. Chizhov, S. N. Terekhin, A. S. Tishchenko
In this work the authors continue their investigation of a millimeter wave weakly relativistic pulse magnetron [1, 2], aimed at the optimization of electric parameters of the device and pointing out the disturbing factors in its efficient performance. The research is illustrated by experimental results featuring the excitation conditions of an 8-mm relativistic magnetron consisting of 48 resonators (RM8). The experiment sought to define oscillations’ frequency and modes and to obtain numerical values of the relations between the generation intensity and the magnitudes of the external static Е- and Н-fields. It was revealed that, over a wide value range of the external fields, the p-mode is the principal oscillation mode of the frequency range under study (37...41 GHz). The paper also reports the results of optimizing the operation modes of generation (pulse high-voltage U0 and external magnetic field induction B0) and their dependence on the geometric parameters of magnetron’s interaction space, namely on cathode’s dimension and the distance between the cathode and anode dса.
A. I. Belyaeva, A. A. Galuza, V. K. Kiseliov, I. V. Kolenov, A. A. Savchenko, E.M. Kuleshov, S. Y. Serebriansky
Ellipsometry is a highly sensitive, non-contact, non-destructive method for studying surfaces and interphase boundaries, based on the study of changes in the polarization state of the probe electromagnetic wave as a result of its interaction with the boundary between the media. A special problem in the analysis of the ellipsometric data are surface defects, which include roughness, island films, regular relief, some localized defects. To date, there are no adequate models describing the effect of localized surface defects on results of ellipsometrical experiments. Previously, it has been suggested that localized defects under certain conditions may not affect the ellipsometric data. The purpose of this work is to test this hypothesis by conducting systematic studies of the influence of defects in the form of parallelepipeds of various sizes on the ellipsometric data. Scale modeling of influence of defects typical for surface subjected to radiation sputtering on ellipsometric experiment results in the optical range has been performed using developed terahertz ellipsometer that operates at wavelength l = 2.2 mm (0.14 THz). Such a large operating wavelength allowed to form on the surface defects of a given shape and size and to investigate their impact on the ellipsometric parameters. A description of the ellipsometer, and the results of systematic studies of the influence of various defects on the surface of the material with strong absorption data ellipsometry are presented. It is first experimentally proved that localized defects of comparable size to the wavelength can be "invisible" for ellipsometry.
O. V. Gurin, A. V. Degtyarev, V. A. Maslov, V. A. Svich, V. S. Senyuta, A. N. Topkov, V. V. Khardikov
Cylindrical vector beams have many applications including electron acceleration, handling materials, a high-resolution metrology, microellipsometry and spectroscopy. Methods and approaches for obtaining beams with complex polarization structure are practically absent in the terahertz range.The method of calculation is proposed and coefficients of reflection and transmission of azimuthally symmetric modes for diffraction mirror in the form of an concentric diaphragm located inside a metal circular waveguide are obtained numerically. With the help of programme solver HFSS the optimal structure of diffraction mirror is found, which allows to reduce significantly the reflection coefficients for modes with nonazimuthal types of polarization. The obtained results can be used to develop new intracavity methods for formation of radiation with spatially inhomogeneous polarization in terahertz lasers.
L. E. Kopilovich
The paper is devoted to building multi-element non-redundant configurations (NRCs) on square and hexagonal grids considered as mathematical models of interferometers. By the regular method based on using planar difference sets, NRCs on grids of large sizes having a maximized number of elements, and also those ensuring complete coverage of the central domains in the spatial-frequency plane (u,v-plane) are built. The estimates of the maximum number of the NRC elements on grids of given sizes are also obtained.
K. A. Vytovtov
It is well known that the communication system with frequency modulation has better noise immunity in comparison with widespread systems with the amplitude modulation. But despite their widespread use in radio frequency domain, in the optical domain such systems do not exist. One of reasons is the lack of detectors of this frequency range. In this paper, for the first time the near infrared frequency detectors (850 nm) are shown, they are based on a layered isotropic structure. The operation principle is described and the basic technical parameters of the devices are calculated. These devices detection is carried out in two stages: at the first stage the frequency change is converted to a amplitude change; at the second stage, detection of amplitude-modulated oscillation is carried out by usual amplitude detectors. Three possible types of detectors are considered: in-phase, inverse, balance. Advantages and disadvantages of the devices have been shown and their application prospects in communication systems have been described. The results can be used in optical communication systems with frequency modulation.