Radio physics and electronics

3-10

Authors: V.L. Pazynin

A rigorous mathematical model of the diffraction of an electromagnetic wave in the bend of a plane-parallel waveguide is constructed. Within numerical simulation of the waveguide bend the effect of its complete locking at a frequency located nearby the critical frequency of the second mode is revealed. The resonant nature of this effect, which consists of excitation of locking oscillation in this waveguide inhomogeneity, is found. The conclusion is that the bend of a waveguide could be considered as an open-type waveguide resonator. The importance of the solved problem is caused by wide waveguide bends applications in the microwave technology.

17-22

Authors: V. G. Sugak

The article presents the results of research on opportunities of revealing a weak target movement in foliage-penetration environment with the use of Stepped Frequency Continuous Wave Radar in the frequency range of 1 200…1 800 MHz. The entropy weighed coherent integration (EWCI) algorithm is adopted to phase fluctuations of radar returns and it allows the multipath effects to be mitigated and the detectability and visibility of targets behind foliage brushes and trees to become significantly better.

28-40

Authors: Yu.P. Galyuk, A.P. Nikolaenko, M. Hayakawa

Accounting for the actual structure of the lower ionosphere in the problems of global electromagnetic (Schumann) resonance is an important and urgent task. The paper analyzes an impact of deviations in the vertical profile of the atmosphere conductivity at the night and the day sides of the planet on the spatial distribution of electromagnetic field in the Schumann resonance band. The cavity characteristics depend on the conductivity profiles and are accounted for at the day and the night sides by using the full wave solution method. The problem in non-uniform cavity is solved with the help of 2D telegraph equation. The shift of the maximum amplitude of the electric field component from the source geometric antipode is demonstrated at several frequencies for different locations of the source, and in the models of smooth and sharp day–night transition. We demonstrate that the day-night non-uniformity is able to shift the antipode maximum of the vertical electric field from the source geometric antipode of the center towards the center of the day hemisphere by a distance reaching 300 km.

50-57

Authors: P. V. Kholod, L. A. Varyanitsa-Roshchupkina, Т. N. Ogurtsova

The causes of afterpulse current oscillations in electrically large loop antennas have been found basing on the analysis of results of simulation of the space-time current distribution induced by electric and magnetic field components in the circular and rectangular loops. It has been determined that the pulse shape distortion is due to the current induced by the electric component of the incident field. For undistorted reception, it is necessary to isolate only the current induced by the magnetic component from the total current. To do this, it is sufficient to sum the currents induced in diametrically opposite sections of the circular loop. It has been found experimentally that undistorted reception can be ensured by summing the signals recorded in diametrically opposite sections of the circular loop.

66-71

Authors: N. N. Beletskii, S. A. Borysenko

The effect of reflectionless normal transit of electromagnetic waves through symmetric three-layered structures containing negative-permittivity layers excites considerable interest. It is stipulated by both an unusual nature of the effect and its unique technical applications. Moreover the electromagnetic-wave reflectionless transit effect has been investigated not enough and not all the peculiarities of the effect have been found and described yet. By now the reflectionless transit effect has been considered only for some concrete values of the permittivity and thickness of a symmetric three-layered structure. In this paper a more general approach based on entering dimentionless values of the thickness of the structure layers is used. This approach makes it possible to study the reflectionless transit effect irrelatively to some concrete wave band. It is shown that the presence of a negative-permittivity layer in a three-layered structure leads to a considerable change in the reflection spectrum of electromagnetic waves. It has been found that in the reflection spectrum of the electromagnetic waves there are wide regions of a weak reflection. The width of these regions can be controlled efficiently by matching a value of the negative permittivity of the middle layer in the three-layered structure. The influence of the energy losses in the middle layer of the three-layered structure on the reflection spectrum of the electromagnetic waves is studied. The obtained results are of great practical importance for developing new devices of electronics, photonics, and photovoltaics.

79-84

Authors: N. G. Kokodiy, A. O. Natarova, V. A. Timanyuk , I. A. Priz

The availability of radio communication, television, radiolocation, remote information processing systems led to the appearance of an intense electromagnetic background in our environment. In many cases, it is the cause of the disturbance of the correct functioning of biological objects, a hindrance to the operation of radioelectronic devices – information transmission systems and military equipment. Therefore, there is a need to protect objects from electromagnetic radiation. Particular attention is given to the development of screens and coatings, the effectiveness of which is achieved through the absorption of electromagnetic radiation, since the reflection of electromagnetic radiation often has a negative effect associated with the formation of a re-reflected wave effecting the screened object. In addition, it can help to identify an object by external sensors in cases where it is undesirable. The effect of an anomalously large absorption of microwave radiation by conducting fibers is observed when electric vector of an electromagnetic wave which falls on a fiber is parallel to the axis of the fiber. The possibility of using this effect to create protective screens is considered in this paper. The study showed that electromagnetic radiation is very strongly absorbed and dissipated by thin conducting fibers if the electric vector of the wave is parallel to the fiber axis: the values of the absorption and scattering efficiency factors can reach several hundred and even thousand, that is, the effective absorption and scattering cross sections can be in several hundred or thousand times higher than the geometric cross sections of the fiber. This is a size effect, the nature of which, perhaps, is related to the effective excitation of currents at certain ratios between the fiber diameter and the wavelength of the radiation. Also in the work, the advantages of graphite fibers in front of metal ones as a material for absorbing screens have been experimentally proved. The results of the study can be used to create protective screens in the microwave range.