NOISE TEMPERATURE OF THE ACTIVE PHASED ARRAY OF THE GURT RADIO TELESCOPE

Abstract

Purpose: Theoretical and experimental investigations of noise temperature of a subarray being a part of the active phased array for the GURT – a low frequency radio telescope of new generation. Design/methodology/approach: A mathematical model of the active phased array is developed in the form of a cascade connection of two noisy multiport networks, one of which is associated with the dipole array antenna placed over imperfect ground, and the other with the beam-forming network. The electrical parameters of these multiport networks are described by the scattering matrices, and the noise parameters – by the covariance matrix of the spectral densities of noise waves. The calculation expressions are obtained which allow analyzing the GURT subarray noise temperature with correct account for all internal noise sources and their mutual correlation which is caused by interaction of dipoles in the array. Findings: Numerical and experimental studies of the noise temperature at the subarray output of the GURT active phased antenna array have been performed. These studies made it possible to estimate the relation between the external and internal noise temperatures in a wide frequency range from 8 to 80 MHz when scanning the subarray beam in the upper hemisphere. It is shown that the external noise temperature at the subarray output is more than 6 dB higher than the internal one in the bandwidth of about 65 MHz. Good agreement between the results of calculation and experiment is obtained, that validates the developed model of the GURT subarray and the effectiveness of the proposed technique for numerical analysis of its parameters. Conclusions: The studies described here confirm the possibility of effective use of this subarray as the base cell of a large phased antenna array for the low frequency radio telescope, as well as the standalone antenna of the radio telescope when radio astronomical observations do not require high angular resolution. The results of this work can be useful in the development and studies of active phased antenna arrays for the decameter and meter wave ranges.

Keywords

• radio telescope
• active phased antenna array
• subarray
• beam scanning
• noise temperature
• scattering matrix
• covariance matrix