RADIO PHYSICS AND RADIO ASTRONOMY

PACS numbers: 52.40.Fd;
52.75.-d

Purpose: Actually, the most vexed problem in developing and creation of new models of military technique is improvement of protection of objects in the radio electronic warfare. The perspective direction of creation of scarcely noticeable antennas is the use of low temperature plasma. Moreover, the plasma antennas can be quickly operated by tuning the working frequency and steering a beam. In plasma antennas, the role of a conductive element plays the gas discharge in a limited space. The efficiency of converting the energy of a surface wave propagating in a longitudinally inhomogeneous cylindrical plasma column into radiation has been studied. A plasma column is limited by a dielectric sheath. A narrow metal cylindrical rod is coaxially located inside the plasma column.

Design/methodology/approach: The analysis was made by the method of spectral expansion of the electromagnetic field of the considered wave-propagating system in a complete set of functions, including surface and spatial waves of the plasma column.

Findings: A system of integro-differential equations for finding the expansion coefficients has been derived. These coefficients determine the amplitudes of the reflected from and scattered on the plasma inhomogeneity waves, and the wave transmitted through the inhomogeneity, as well as the radiation pattern. The system of equations is valid for an arbitrary longitudinal change in the plasma density. The dependences of the transformation coefficients of the surface wave energy on the plasma density gradient are calculated for some values of the plasma cylinder electric radius and dielectric constant. Examples are given when the fraction of the surface wave energy being transformed into the radiation at sharp angles can make 25 to 30 %. The radiation patterns are pointed and have one well-defined lobe. The maximum radiation occurs at an angle of several degrees with respect to the surface wave propagation direction. The lobe width decreases, and its position shifts to 0° with an increase in the plasma density gradient. The influence of the properties of the dielectric and the metal rod radius on the radiation characteristics is investigated.

Conclusions: The here-considered wave-propagating system is an adequate-enough model of a plasma antenna. The energy being entered into such an antenna is converting with high efficiency into the radiation at small angles to the axis.

Key words: cylindrical plasma antenna, spectral decomposition method, radiation, surface waves, directional pattern, low-temperature plasma

Manuscript submitted  12.02.2020

Radio phys. radio astron. 2020, 25(2): 158-167

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