Vol 63, No 8 (2018)
- Year: 2018
- Articles: 16
- URL: https://journals.rcsi.science/1064-2269/issue/view/12473
Electrodynamics and Wave Propagation
Periodic Arrays of Magnetoelectrically Excited Double and Single Split-Ring Resonators as Artificial Magnetic Conductors
Abstract
The amplitude and phase of the reflection coefficient of periodic arrays of electrically conducting elements in the form of double and single split rings are determined for two orientations of these rings, corresponding to magnetic (H) and magnetoelectric (HE) excitation. It is shown that, in the case of the HE-excitation of the rings, the arrays possess the properties of an artificial magnetic conductor or a high-impedance surface. The electric and magnetic fields near the arrays are calculated, and the dependence of the impedance on the distance between the array and the plane in which the impedance is determined is obtained. It is shown that the maximum of the impedance is in close vicinity of the array and can amount to tens of thousands of ohms. The feasibility of implementing a modified Salisbury radio absorber of small thickness by means of such arrays is shown theoretically and experimentally. It is also shown that, under illumination of an array of limited dimensions by a closely placed dipole, the screening effect reaches –30 dB with good matching of the dipole to the feed line (the reflection coefficient in the line is less than –20 dB).
The Influence of a Finite Size of Spheroids Forming a Chain on the Properties of Surface Plasmons
Abstract
A plasmon transmission line comprising a chain of metal nanospheroids is considered. It is shown that taking into account a finite size of spheroids leads to a significant change in the transmission characteristics of the chain of spheroids; in particular, the plasmon propagation length decreases dramatically.
Radio Emission of the High-Latitude Ionosphere as a Result of the Cutoff Mode of the Auroral Ionospheric Duct
Abstract
Issues of radio emission of the auroral ionosphere are considered with the use of the classical electrodynamics approach, according to which a natural waveguide is formed in the Earth’s ionosphere owing to formation of a trough in the high-latitude ionosphere. Parameters and characteristics of the auroral ionospheric dielectric duct have been estimated on the basis of the obtained experimental data on the properties of the ionospheric trough. The hypothesis that the LF and VLF electromagnetic auroral radio emission in the high-latitude ionosphere is due to the approach of the auroral waveguide to the cutoff mode has been considered. It has been found that the radio emission bands correspond to the eigenmodes of the ionospheric duct under consideration. It has been shown that, within the proposed approach, not only the radio emission frequency band of the high-latitude ionosphere but also the polarization of the radio emission observed in the experiments can be explained.
Electrodynamic Characteristics of Dipole Antennas Made of Graphene-Containing Carbon Fiber Composite Materials
Abstract
The electrodynamic characteristics of dipole antennas made of carbon fiber composites with a graphene-containing binder have been investigated at 200 and 600 MHz. It is shown that main characteristics of antennas, including the standing wave ratio, radiation pattern, and gain factor, coincide with characteristics of their metal analogs. The effect of conductive properties of the metal–carbon fiber composite contact in the dipole radiating elements on the parameters of the antennas is estimated.
Antenna and Feeder Systems
Emission of High-Power Ultrawideband Elliptically Polarized Pulsed Radiation by a Cylindrical Helical Antenna
Abstract
Ultrawideband elliptically polarized radiation is numerically and experimentally studied. The analysis is performed for the axial radiation of a cylindrical helical antenna that is excited by a bipolar voltage pulse with a duration of 2 ns. The results are used for construction of a source of high-power ultrawideband pulses with elliptical polarization. The radiation pulses with an effective potential of 300 kV are generated at an amplitude of the bipolar voltage pulse of 200 kV and a repetition rate of 100 Hz.
Theory and Methods of Signal Processing
Navigational cosGBOC Signals in Promising Satellite Radio-Navigation Systems
Abstract
The formation and structure of the modulation function (MF) of cosine generalized binary offset carrier (cosGBOC) signals applied in promising satellite radio-navigation systems, such as Galileo (European Union), global positioning system (GPS) (USA), and BeiDou/Compass (China), are discussed. Analytical expressions for the spectral density and energy spectrum characterizing the single components of cosGBOC-signal MFs are derived at the different values of pulse multiplicity coefficients NR (NR=2, 4, 6, …) and duty cycles ρ (ρ ∈ [0, 1]). The obtained general formulas for cosGBOC signals are employed to analyze spectra in the important particular cases of cosGBOC and BPSK signals. With the help of the Mathcad software package, the graphs of the energy spectra of the single components entering into the cosGBOC-signal MF are constructed for the following types of modulation: cosGBOC(1, 1, ρ), cosGBOC(2, 2, ρ), and cosGBOC(10, 5, ρ). The properties of the given energy spectra are investigated.
Pulsed Phase-Shift Keyed Signals with Zero Autocorrelation Zone
Abstract
A coherent additional signal whose zero side-lobe region (its relative width lies in the interval [1 3,1)) is located near the central peak of an aperiodic autocorrelation function is synthesized. It is demonstrated that the given signal is the batch composed of two phase-shift keyed pulses encoded by paired or adjacent sequences of the D-code with the length N = 2k signal synthesis is proposed to generate from a set of the N/4 ensembles of D-code with length N. The correlation characteristics of the synthesized signal are analyzed.
Linear Minimax Filtering of a Stationary Random Process under the Condition of the Interval Fuzziness in the State Matrix of the System with a Restricted Variance
Abstract
The equations for the transition functions of optimal minimax filters are derived under the condition of the interval fuzziness of the linear dynamic system with the parametric uncertain assignment of only the state matrix in the context of Hurwitz stability. The method by which the required filter is synthesized as the suboptimal minimax filter of the stable and unstable first-order systems with the given degree of stability is discussed.
Radio Phenomena in Solids and Plasma
Electrostrictive Mechanism of Liquid Breakdown in Strongly Nonhomogeneous Field under the Action of Nanosecond Voltage Pulse
Abstract
Electrostriction mechanism of breakdown in polar liquid caused by high-voltage nanosecond pulse is studied. Nonstationary motion of liquid in the pin-to-plane system exposed to a pulse with peak voltage of 30 kV and 6-ns duration is numerically analyzed. Cavities in which the breakdown can be initiated are formed in the vicinity of the tip electrode. Dimensions of such cavities are estimated, and the conditions for formation are formulated. Profiles of voltage and current pulses are measured for breakdown in water and air. The velocity of breakdown development in air is determined using the time delay of the pulse measured by the shunt of discharge current at several interelectrode distances. The proposed method has limitations in the measurement of breakdown in water due to the effect of displacement current that exceeds the discharge current.
Cutoff Angles of the Backward Spin Wave in a Tangentially Magnetized Ferrite Plate
Abstract
The cutoff angles for the wave vector and the group velocity vector of a backward spin wave propagating in a tangentially magnetized ferrite plate are calculated. It is established that the expressions for these angles do not depend on the mode number and coincide with the analogous expressions for the corresponding cutoff angles of a spin wave in an unbounded ferromagnet. It is found that the regions corresponding to all possible orientations of the wave vector for the backward and surface spin waves in a ferrite slab and for a spin wave in an unbounded ferromagnet are adjacent and nonintersecting. It is shown that, if the isofrequency dependence of the wave has inflection points, then the range of all possible orientations of the group velocity vector of the wave can be wider than the angular interval enclosed between the cutoff angles for the group velocity vector.
On the Theory of Beam-Plasma Instability in the Nonstationary Plasma
Abstract
The beam instability in the plasma with density slowly varying with time has been investigated using the potential approximation. It has been shown that a frequency shift occurs in the amplified signal propagating in such an electrodynamic system; analytical relations for determining the value of this shift have been obtained. It is demonstrated that the frequency is shifted most strongly as the plasma density decreases, when the Langmuir frequency of plasma electrons approaches the signal frequency and the instability increment increases with time.
Increasing the Efficiency of Terahertz Generation during the Current Flow through Magnetic Junctions Formed by Inhomogeneous Ultrathin Films of a Ferromagnetic Metal
Abstract
Operating modes of terahertz (THz) generators with “rod–film” magnetic junctions formed by a Fe rod with one pointed end with a diameter of 10–50 nm and various nanometer-thick (single-layer and multilayer) Со films are studied. It is demonstrated that the efficiency of the THz radiation increases (due to an increase in the current density) if the thickness of a single-layer film decreases to the point when it becomes discontinuous (ultrathin) while retains its conductivity. If a multilayer structure with several such films separated by nonmagnetic conductive layers is used, the radiation power can also be increased.
Microwave Electronics
Two Methods for Miniaturization of Stub Quadrature Couplers
Abstract
Two circuit-topological methods for reducing the overall dimensions of stub quadrature coupler (SQCs) are considered. The essence of the presented methods lies in replacing quarter-wave stubs with low-pass filters and artificial transmission lines (ATLs). It is shown that, using these methods, it is possible to reduce dimensions of two-stub and five-stub coupler by 71.9%. The design and experimental characteristics are presented; it is found out that the band of operating frequencies of compact SQCs is 1.4 times less than the bandwidth of conventional coupler and the imbalance of the power division coefficient increases.
Nanoelectronics
Structure and Spectral Dependences of the Raman Scattering of Photosensitive CuIn0.95Ga0.05Se2 Films on Glass, Aluminum, and Nanoporous Al/Al2O3 Substrates
Abstract
Photosensitive polycrystalline CuIn0.95Ga0.05Se2 thin films have been formed on glass, aluminum, and nanoporous Al/Al2O3 substrates by means of two-step selenization in a gas (nitrogen) flow carrying a reaction component (selenium). The structural properties and the Raman scattering spectral dependences have been investigated. The dependence of the main lattice parameters and intensities of the Raman scattering lines on the substrate material is demonstrated.
Electron and Ion Optics
Novel Radio Systems and Elements
Formation of Weighting Coefficients in an Artificial Neural Network Based on the Memristive Effect in Metal–Oxide–Metal Nanostructures
Abstract
An approach to formation and training of an artificial neural network (ANN) based on thin-film memristive metal–oxide–metal nanostructures, which exhibit the effect of bipolar resistive switching, has been proposed. An experimental electric circuit of a small-sized ANN (a two-layer perceptron with 32 memristive elements) has been constructed. An algorithm for formation of weighting coefficients (ANN training), which takes into account probable spread of technological parameters of memristive structures has been developed.