Radio Physics and Radio Astronomy (Dec 2019)
EFFECT OF THE GROUND PARAMETER VARIATIONS ON THE SENSITIVITY OF AN ACTIVE PHASED ARRAY ANTENNA ELEMENT OF THE LOW-FREQUENCY GURT RADIO TELESCOPE
Abstract
Purpose: Theoretical studies of sensitivity fluctuations of a phased array antenna element for the GURT radio telescope of the new generation caused by seasonal changes of the ground parameters. Design/methodology/approach: A mathematical model of an active antenna represented as a two-port network, whose electrical parameters are described with the scattering matrix and the noise parameters – with the covariation matrix of noise wave spectral densities was used for studying the GURT phased array antenna element composed of a dipole and a low-noise amplifier (LNA). Such a model allows a correct analysis of a signal-to-noise ratio at the active antenna output accounting for all internal and external noise sources. Findings: A numerical analysis of the GURT radio telescope phased array antenna element characteristics was made in a wide frequency range of 8 to 80 MHz. It was found that the seasonal fluctuations of permittivity and conductivity of the ground, which make about 8 and 6 dB correspondingly, mostly affect the dipole efficiency and its impedance matching with the LNA. Variations of both parameters reach 3 dB but have the opposite sign, therefore their effect upon the active antenna sensitivity is mostly compensated. As a result, it is shown that the seasonal fluctuations of the ground parameters do not result in the substantial active antenna sensitivity variations, which lay in about the 0.5 dB range, and only at the lowest frequencies grow to about the 1.5 dB value. Conclusions: The research efforts made have shown that the seasonal fluctuations of the ground electrophysical parameters result in small variations of the sensitivity of the GURT phased ±0.75 dB, which cannot array antenna element, not exceeding affect the quality of radio-astronomy observations considerably. The results of this work can be useful in the development and researches of the ground active phased array antennas designed for operation in the meter and decameter wavelength ranges.
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