Radio physics and electronics

9-21

Authors: V. V. Ovsyanikov, E. R. Beznosova

Subject and Purpose. The results of studies of actual methods for expanding the frequency range of vibrational curved whip and loop antennas, and antenna arrays based on them are presented. Optimal designs of broadband antennas with the concentrated reactive loads included in the shoulders are considered. Methods and methodology. Calculations of the electrical parameters of the antennas were performed by the integral equation method, which allowed us to investigate new variants of broadband pin and loop antennas and antenna arrays more deeply. Two types of antennas are investigated, which are promising for the use in the microstrip implementation in the form of single antennas and as part of antenna arrays. The first variant is a Z-shaped antenna of orthogonal linear polarization, supplemented by concentrated capacitive loads; the second one is a loop in the form of a frame also with capacitive loads. To approximate the actual application conditions, the antenna parameters were determined when they were placed at a small height above the conductive screen (plane). Results. As a result of calculations of the electrical parameters of Z-shaped antennas with capacitive loads and antenna arrays based on them in the wide frequency range of 0.9...1.2...2.7 GHz, we obtained a significant improvement (decrease) in the standing wave voltage coefficient up to values not exceeding five in comparison with similar antennas without loads, for which the values of this parameter reach thirty or more. Compared with conventional rectilinear antennas of the same length and thickness of the rod, the antenna gain factor with loads increased from 7.8 to 9.8 dB at a decrease in the standing wave voltage coefficient from 3.5 to 3.1 at the middle frequency of the investigated range. For loop antennas with capacitive loads, the values of the standing wave voltage coefficient were not more than five in the same range, and at the middle frequency of the range these values did not exceed 1.9, while in antennas without loads this parameter is much higher (up to thirty) and at the middle frequency of the band has a relatively high value up to 15. Coplanar linear in-phase antenna arrays of three Z-shaped and three loop antennas with capacitive loads have been investigated. It is shown that due to the difference in the conditions for the mutual arrangement of the antennas in the gratings, the standing wave voltage coefficient of the terminal array antennas differs from this parameter of the average antenna. Conclusions. To obtain the operating mode of a current close to the traveling wave mode in Z-shaped and loop antennas and antenna arrays based on them, and, as a consequence, to reduce the frequency dependence of the input parameters and radiation patterns of these antennas, it is sufficient to include no more than four capacitive loads in the symmetric antenna arm. This makes it possible to simplify broadband antennas and save the expenses of time and resources for their development and fabrication in comparison with the known works, where it was proposed to include several tens of capacitive loads in the antenna arm.

39-47

Authors: O. V. Sytnik, G. P. Pochanin, S. A. Masalov, V. P. Ruban, P. V. Kholod

Subject and Purpose. The subject of the study is a measuring system consisting of several spatially separated receiving points and a transmitter emitting video pulse signals. The aim of the work is to create an effective algorithm for processing signals from a multi-position observation system under conditions of correlated jamming to solve the problem of the operational detection of mobile objects hidden behind optically opaque obstacles. Methods and methodology of work are based on the difference-distance-measuring principle of calculation of the target coordinates. The informative signal from the target is not identified by direct methods because of the multiple reflections of the sounding signal from the walls of the room and objects located inside it. The procedure for suppressing the interference reflections of the probing signal is developed. The accumulation of a signal and the removal of interference is carried out in real time by subtracting the alternating samples of the observed process from the signals of each receiving point assuming that the object is slow moving or practically unmoving during the time of sounding signal propagation from transmitter to target and back. The delay of the probing signal during its propagation from the transmitter to the target and from the target to each of the receivers has been estimated using the proposed peak factor criterion. The same criterion is used to reject the struck lines on the radar image of the target's trajectory. Results. A high-speed algorithm is developed which, at the condition of a relatively high signal-to-noise ratio, makes it possible to use the signal peak factor as a criterion for jammers suppression at the radar's image. The simplicity of signal processing allowed to continuously display the data in a user-friendly form. The continuity of measurements of the delays of the reflected signals from the target to the receiving points is ensured by polynomial approximation of the object trajectories relative to each of the receivers. Conclusions. The high energy characteristics of the observation system, the stability of the parameters during the measurements, and the high accuracy of the reflected waveform reproduction allowed us to use digital signal processing methods in real time. The simulation results are confirmed by data that were accumulated and averaged over a series of similar experiments.

54-60

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

Subject and purpose. The effect of reflectionless transmission (tunneling) of electromagnetic waves through the three-layer structure containing a negative-permittivity layer is of great importance both for studying the fundamental properties of solids and for developing new types of unique technical devices. There is a need for investigation of the effect of reflectionless transmission of electromagnetic waves through the three-layer structure containing a negative-permittivity layer in a wide range of the three-layer structure parameters. Methods and methodology. A new approach based on the use of dimensionless thicknesses of a three-layer structure is presented. This approach makes it possible to study the effect of reflectionless transmission of electromagnetic waves for different wavelengths and different values of parameters of the three-layer structure with asymmetric dielectric surroundings. Results. It is shown that the presence of a negative-permittivity layer in the three-layer structure leads to a significant softening of limitations on the parameters of the positive-permittivity layers. Thus, the effect of reflectionless transmission of electromagnetic waves takes place at any preassigned positive value of the permittivity of the layers surrounding symmetrically the negative-permittivity layer. In this case, the parameters of the negative-permittivity layer should be chosen as required. Conclusions. The results of the research extend knowledge on the mechanisms of electromagnetic waves tunneling through the three-layer structures containing negative-permittivity layers. This effect can be used for development of new types of high-frequency solid-state devices operating in different wavelength ranges

69-75

Authors: M. I. Dzyubenko, Y. E. Kamenev, V. P. Radionov, Z. Y. Litvina

Subject and purpose. The terahertz frequency range currently attracts much attention due to the wide possibilities of its application for solving a number of problems in science, technology, and medicine. In this range, metal gratings with the period shorter than the wavelength are widely used as partially transparent mirrors of lasers and in various quasi-optical devices. The determination of the parameters of such gratings is an actual problem. Methods and methodology. The method of experimental comparison of the parameters (losses and transmittance) of metal gratings consisting of parallel conductors is presented in the paper. A THz laser with a smooth adjustment of the output of laser radiation from the resonator was used as a measuring device. The investigated metal grating serves as the exit mirror of this laser. The dihedral 90° mirror is the second mirror of the laser resonator. The adjustment of feedback is performed by rotation of the dihedral mirror around the resonator axis. The angle of rotation of the dihedral mirror, which provides the maximum power of laser radiation, characterizes the transmittance coefficient of the investigated grating. The value of the maximum power of laser radiation characterizes the magnitude of the losses in the investigated grating. This allows one to compare the grating parameters experimentally without the use of metrological instruments. Results. An experimental comparison of the parameters of metal gratings with different structures was carried out as an approbation of the method. Recommendations for the increase of the measurement reliability and further advancement of this method were developed. Conclusions. The proposed method is an effective tool for comparing the transmittance and loss factors in one-dimensional metal gratings for their control and culling. In addition, this method can serve as a measuring device, when reference gratings with known parameters are used for comparison.