Radio physics and electronics

3-10

Authors: L.P. Mospan, А.А. Kirilenko, D.Yu. Kulik, S.О. Steshenko

Subject and Purpose. Peculiarities of the electromagnetic wave scattering at screens perforated by U-shaped slots are the subject of the paper. Numerical modeling of frequency-selective surfaces with frequency characteristics given and research into the possibilities of the performance control of the screens by complicating their elementary cell geometry are the purposes of the paper. Method and Methodology. The numerical modeling is performed upon the MWD3 software package developed in the laboratory of computational electromagnetics of the IRE NASU. Based on the scattering mode technique and the mode-matching technique taking into account the electromagnetic field behavior near the edges, this software package enables calculations of scattering characteristics of both compound waveguides and gratings with piece-wise boundaries. Results. A virtual waveguide was incorporated into the MWD3 projection schemes, extending capabilities of the MWD3 software and making it possible to treat the frequency-selective surfaces with piece-wise boundaries without adding new building blocks. Numerical modeling of perforated screens with U-shaped slots was carried out. Conclusion. Configurations of single and double metal screens and, also, a compound grating formed by two screens separated by a dielectric layer were calculated in full agreement with the given task. The perforated screens provide essential reflectivity decrease at low frequencies and, also, a low insertion loss level in the given millimeter wave region. The obtained results can be of interest for specialists in antenna-feeder engineering and for MWD3 software users.

21-27

Authors: D.M. Bychkov, V.K. Ivanov, A.Ya. Matveev, V.N. Tsymbal, S.E. Yatsevich

Subject and purpose. The purpose of this work is to study the effect of wind on the anomalous scattering of radio waves during aeolian processes of sand and dust transporting. Мethods and methodology. The article analyzes the spatial variations of the near-surface wind and their effect on the characteristics of anomalously narrowly directed radio wave backscattering according to the long-term studies of desert regions of Al-Jouf, Akshar and Trarza in Mauritania by Envisat-1 satellite SAR. Results. Analysis of SAR data indicates that intensity of radio wave scattering on the leeward slopes of sand ridges is more than 12...15 dB higher than the one from the slopes located in the "wind shadow" zone, which indicates the direct influence of the surface wind on the back scattering of radio waves during aeolian sand and dust transportation. The dependences of changes in the backscattering coefficient s 0 on the angle of local irradiation q along sections of fragments of homogeneous sections of the surface radar images are obtained. Conclusion. SAR data indicate that the spatial distribution of the maximum intensity values of anomalously narrowly directed backscattering of radio waves corresponds to the spatial distribution of the near-surface wind. The intensity of backscattering of radio waves, starting at a speed of 2 m/s and higher, steadily depends on the wind speed.

38-49

Authors: M.V. Balaban, Y.V. Goncharenko, V.M. Gorobets, O.L. Kovorotniy, F.V. Kivva, G. Farquharson

Subject and Purpose. The paper is concerned with Synthetic Aperture Radar (SAR) imaging and data processing and seeks to modify the conventional time-domain back projection algorithm (BPA) used for creating a SAR image. The modification consists in the radar squint-angle control at the stage of data processing. Methods and Methodology. Mathematical modeling methods are used. The modeling results are verified by reference to the experimental data. Results. A modification proposed for the back projection algorithm (BPA) enables fast-moving targets to be detected on a stationary image created by synthetic-aperture squint-angle side-looking radar. The back projection algorithm with the squint angle control was experimentally verified by a speedboat example to show that the SAR image has signatures of fast-moving targets which are not observed on the image formed by the classic back projection algorithm. Conclusion. The proposed modification of the back projection algorithm improves the detection probability of fast-moving targets on a SAR image and does it without any complication of the classic back projection algorithm or additional computing time.

60-69

Authors: Yu.O. Averkov, Yu.V. Prokopenko, V.M. Yakovenko

Subject and Purpose. The creation of millimeter and submillimeter electromagnetic wave generators is a promising direction in radio physics. These generators are demanded in medicine, biology, spectroscopy, broadband wireless communications and other branches of science and technology. One of the ways of millimeter and submillimeter wave generation is interaction between charged-particle beams and super-dimensional electrodynamic structures in multimode operation. In this regard, elementary physical mechanisms underlying this interaction invite further investigation. In the paper, the problem of spatial-surface eigenmode excitation is considered for a solid-state cylinder when a nonrelativistic electron moves in a vacuum over the surface of this cylinder and parallel to its axis. Because of the nonrelativistic character of the electron motion, the electron field and the radiation field in a vacuum are treated in the electrostatic approximation, while the fields inside the cylinder are calculated with the delay effect taken into account. Methods and Methodology. Maxwell’s equations in space-time field terms yield an analytical expression of the electron energy loss for the spatial-surface eigenmode excitation of a dielectric cylinder. This expression is numerically analyzed using the bisection method to find roots of the dispersion equation. Results. The analysis of the electron energy loss suggests that the E-type modes are the most efficiently excited. The electron energy loss for the E-mode excitation is approximately two orders higher than the loss for the excitation of H-modes with the same azimuthal and radial mode indices. The largest electron energy loss corresponds to the HE11 mode excitation. Conclusion. The performed study gives a deeper insight into the physical mechanism underlying the eigenmode excitation of a dielectric cylinder under the action of charged particles. The obtained results can be generalized to the case of a multijet electron beam used to generate whispering-gallery electromagnetic modes.

80-85

Authors: M.А. Miliaiev, S.V. Nedukh, S.I. Tarapov

Subject and Purpose. The paper presents the development and testing of a microwave splitter based on a planar hyperbolic metamaterial with a structural defect. The planar hyperbolic metamaterial is so constructed that a propagating electromagnetic (EM) wave is channeled in a certain direction depending on the metamaterial parameters. The wave splitting is possible where a part of the incident wave is reflected from a defect created inside the metamaterial. As the defect spatial orientation relative to the incident EM wave changes, the propagation direction of the reflected EM wave also changes. By this means the wave propagation control can be implemented in the considered splitter. Methods and Methodology. A defect in a planar hyperbolic metamaterial is created using the circuit theory that relates the material parameters to the equivalent unit-cell capacitances and inductances which, in turn, depend on the parameters of the microstrip line and capacitors. Thus, a change in any parameter of the circuit inside the unit cell changes its material parameters and makes a defect cell. In this work, a defect is created by changing the capacitance of the capacitors in a given set of elementary cells of a planar hyperbolic metamaterial, controlling thereby the size of the defect and its spatial location relative to the propagating wave. The numerical model of EM wave propagation inside a planar hyperbolic metamaterial with a defect is validated by experiment. In it, the field distribution over the metamaterial surface is obtained using the active probe method in the three cases: a defect-free metamaterial and two variants of defect orientation. To insert the electronic control, it is proposed to replace the elementary cell capacitors with varactors. Results. The obtained field distributions show that the defect partially reflects the incident EM wave channelized in the planar hyperbolic metamaterial. As the defect location angle changes, the wave reflection angle also changes. To make a defect unit cell, it will only suffice to change its capacity by 20% from the original, which is quite feasible in modern varactors. Conclusion. The performed studies have shown that the considered planar hyperbolic metamaterial with a structural defect is good for creating tunable electromagnetic wave splitters.