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15Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2019
NONLINEAR DISTORTIONS OF THE SIGNAL RADIATED BY PLASMA
ASYMMETRIC DIPOLE ANTENNA
N.N. Bogachev1,2,3, N.G. Gusein-zade12, I.L.Bogdankevich12, A.M. Ignatov12, S.E. Andreev1,2
1Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia,
e-mail: bgniknik@yandex.ru 2Pirogov Russian National Medical University, Moscow, Russia, MIREA - Russian Technological University, Moscow, Russia.
Plasma asymmetric dipole antenna (PADA) is an analogue of a metal asymmetric dipole antenna (MADA) with a round screen, and consists of a pin (dipole arm) connected to the central conductor of a coaxial cable and a conductive disk connected to an external conductor of a coaxial cable [1]. In the case of a plasma antenna, the metal pin is replaced with a gas discharge tube with a plasma. Plasma in a tube can be generated either by an external source connected to a gas-discharge tube, or by a source of a radiated high-frequency signal (generator or coherent transmitter). Creating a plasma in the discharge tube of the PADA due to the signal energy from a transmitter allows you to simplify the connection pattern of the plasma antenna and make it similar to the MADA connection. The most convenient way to power a PADA from the transmitter, as in the case of a MADA, is to connect using a coaxial cable. With this method of connection, the plasma gas discharge tube is connected to the central (inner) conductor of the coaxial cable, and the screen is connected to the external conductor of the coaxial cable. In [1], the radiated signal spectrum of PADA was studied and compared with the one of MADA. As a result of studies, nonlinear distortions of the signal (similar to the case in [2]) radiated by the PADA, expressed in amplification of the second, third and fourth harmonics of the input signal frequency, were found.
In this work, experimental and numerical studies of the radiated signal spectrum by a quarter-wave PADA were carried out. The PADA corresponded to the frequency range 450-500 MHz. Experimental measurements of the signal characteristics were carried out on a specially assembled stand, the measurement results were compared with the characteristics of a similar metal antenna. Numerical simulation was carried out in the full electrodynamic code KARAT [3] using the FDTD method using the PiC method as a plasma model. The analysis of the obtained results of numerical simulation was carried out and analytical evaluations were carried out.
As a result of experimental and numerical studies, as well as analytical evaluations, it has been shown that the amplification of multiple harmonics of the input signal frequency during the emission of PVBA is associated with the interaction of the electromagnetic field of the signal and plasma electrons. The amplification is caused by the resulting uneven plasma concentration of electrons in length due to their oscillations in the field of the applied wave. It is shown that nonlinear distortion of the signal increases with increasing field strength in the plasma, which may be caused by an increase in the amplitude of the input signal from the generator or field strength at the corners of the design connection of the discharge tube and coaxial cable.
The report is dedicated to the memory of Professor A.A. Rukhadze. This work was supported by the Russian Foundation for Basic Research, project No. 16-08-00859 a.
References
[1] N.N. Bogachev et. al. Plasma Phys. Rep. 2019 45(4) (in published).
[2] V.N. Konovalov et. al. 2014. XLI Zvenigorod International Conference on Plasma Physics And Controlled Fusion, Russia, 10-14 February.
[3] V. P. Tarakanov. User's manual for code KARAT. 1992. Springfield: BRA.
