Radio physics and electronics

10-18

Authors: Yu. A. Pedenko

The paper focuses on the problem of increasing the accuracy of radar measurements of the elevation angle of the low-altitude targets over the sea. The Matrix Pencil method, as one of the means to resolve this problem, is studied in the paper. This method refers to the methods of high spectral resolution, but in a number of publications, the possibility of its use for measuring the angles of arrival of radio waves is also considered. However, the extent of its suitability for solving the problem needs to be studied taking into account the specific conditions under which the measurement of the elevation angles of low-altitude targets is performed. The research was carried out by computer simulation. It covered the sea states with the conditions of both specular and strong diffuse reflection satisfied. One of the main goals of this work was to determine ultimate measurement accuracy achieved by the method when only the diffuse reflection from the sea is considered as a disturbance (a specular signal along with a direct signal from the target are considered as a measured signal). It was established that by this indicator the Matrix Pencil method does not concede to the well-known MUSIC method, but even exceeds it, especially for strong diffuse reflection (improvement reaches 20%). Another impor-tant task was to investigate the influence of the a priori parameters of the method on the measurement errors: the number of measured signals, the values of the so-called pencil-parameter and the number of spatial samples of the signal at the given antenna aperture. As a result, recommen-dations on the selection of these parameters have been developed, which make it possible to minimize the errors in the measurement of the elevation angles. This research expands the understanding of ways to increase the accuracy of mea-suring the angles of low-altitude targets over an agitated sea.

34-41

Authors: V. D. Karlov, Yu. V. Kirichenko

In the present paper, the plasma antenna with azimuthally asymmetrical traveling waves operating at a harmonic with an azimuth number m = 1 is investigated theoretically and numerically. In addition, the collisions of electrons with atoms are taken into account. Plasma is assumed to be cold and isotropic. The method of the dispersion equation is used. The propagation constant and the attenuation coefficient of the traveling wave can be obtained from the real and imaginary parts of the solution of this equation, respectively. In order to find the radiation patterns (RP), the delayed potentials in the far zone are calculated. The RP strongly depends on the slowing of waves in the antenna. The dependences of the slowing of the wave on the plasma density are obtained, and the dependence of RP on the plasma density, geometrical parameters of plasma cylinder and frequency of electron-atom collisions is investigated. The minimum values of plasma density, at which the normalized radiation patterns are highly directional and have a main lobe located at a zero angle to the antenna axis, are obtained. Advantages of antenna operating at harmonic with m = 1, as compared to the antenna working on an azimuthally-symmetrical wave, are shown: the working plasma density of such antenna is much lower; the radiation is in a strictly axial direction; a small level of the side lobes of the RP; the RP is less dependent on the electron-atom collisions. It is also shown that, by dispersion properties, a plasma antenna with m = 1 is closer to a metallic antenna than an antenna with m = 0.

53-60

Authors: V. А. Markov, V. D. Naumenko

One of the main problems faced by developers of modulators for spatial-harmonic magnetrons with cold secondary emission cathode is the selection of the correct shape of an anode voltage pulse that will ensure the stable operation of the magnetron. In this paper, the effect of the shape of the anode voltage pulse on the operation of transmitters based on magnetrons with cold secondary emission cathodes is investigated. The influence of different parts of the pulse on such parameters of the magnetron as the required current of the starting cathode necessary for stable excitation of secondary emission from the cold cathode, the stability of operation on the selected mode of oscillation, and the generation of the maximum power is experimentally studied. It is shown that the magnitude of the starting cathode current is determined, first of all, by the steepness of the pulse front. Its optimum value is usually about 150 kV/ms. In this case, starting cathode should provide a current of only a few tens of milliamperes, which can significantly increase the lifetime of the device. The article also shows that the presence of a pulse spike at the beginning of a voltage pulse facilitates a premature transition to a non-working mode of oscillation. As a result, this leads to a decrease in the output power of the magnetron. The duration of the decay determines the ability of the magnetron to operate at small pulse duration. For very short pulses, the energy expended on the microwave generation can be equal to the energy expended on the formation of the pulse decay. As a result, it was concluded that the usage of spatial-harmonic magnetrons with cold cathode requires a careful refinement of the characteristics of a pulse modulator. The steepness of the front of its output pulse should be about 150 kV/ms, and the pulse spike at the beginning of the voltage pulse should be as small as possible. When working on very short pulses it is necessary to provide a longer rate of pulse decay.

71-81

Authors: А. О. Puzanov

The torch discharge (TD) is applied in a number of areas of science and technology. However, the lag in theoretical research from ever-growing urgent needs makes the solution of many practical-oriented problems related to the TD relevant. In the present paper, the study of the proposed by the author original method for measuring the resistance of the TD (Rd) taking into account the TD inductance L is continued. The presented numerical calculations are supplemented by the previously performed estimations of the theory application area. The sought resistance Rd is considered as frequency independent within the theory. Performed estimations and calculations confirm the applicability of the approach presented both with and without taking into account the TD inductance in the frequency range from 1·10 ‑3 to 3.0 GHz. It is shown that a necessity to account the inductance of the torch discharge of the power below 1 kW and the choice of appropriate frequency pairs f0,1 have to be studied in each case separately. A possibility to excite the torch discharge at two sufficiently different frequencies is mandatory. Numerical calculations of Rd without taking the inductance into account show that calculations accuracy depend weakly on the height of the torch discharge location relative to the ground. The accuracy increases if the discharge diameter decreases; the discharge length increases; the value of Rd is small and less than 1 kОhm; f0,1 frequencies converge. It results in a necessity to add an equivalent inductance into the Neiman’s scheme making appropriate modifications of the calculation formulae. It is shown that the resonant frequency fr is approximately proportional to fmax, which is the upper limit of the frequency range where the circuit theory remains applicable for the discharge modeling. Thus, the knowledge of fr and fmax allows one to refine the values of the function a, which is the ratio of voltages at which the electrical and geometrical characteristics of the torch discharge remain unchanged. The approach proposed results in more effective using of industrial resources.