Vol 63, No 8 (2018)

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).

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.

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.

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 N_R (N_R=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.

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.

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.

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.

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.

Photosensitive polycrystalline CuIn_0.95Ga_0.05Se₂ 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.

Problems of formation and transport of relativistic electron beams with straight axis and near-rectangular cross section keeping its initial orientation in the process of evolution are considered.

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.