A. I. Sinani1, V. I. Gridnev2

1, 2 JSC “V. Tikhomirov Scientific Research Institute of Instrument Design” (Zhukovsky, Russia)

Measuring the system values of the noise figure and noise temperature of AESA is difficult for developers because of the uncertainty in the gain of the equivalent receiver and the point at which they are measured. This leads to problems of quality assessment, certification of finished products and comparison with foreign products. The method for measuring the system values of the noise figure and noise temperature of the AESA has been considered, which consists in determining the parameters of a single-channel circuit equivalent to the AESA. Reduction of a multichannel system to a single-channel system makes it possible to apply classical noise characteristics to AESA. To measure the gain of an equivalent circuit amplifier, the AESA is placed in the isotropic noise environment in which the brightness temperature of the noise sources is constant on the sphere surrounding the antenna. Such conditions are well modeled in the Anechoic Shielded Chamber (ASC), and the brightness temperature of the ASC noise sources is approximately equal to the temperature of the chamber T. For any passive antenna, without losses, under such conditions, regardless of its radiation pattern, the noise temperature at the exit is equal to the temperature of the chamber. The same noise temperature will be at the input of the equivalent circuit amplifier. By measuring the power spectral density of the noise at the AESA output at different camera temperatures, you can calculate the gain of the equivalent amplifier for noise signals. The described technique is reflected in the terminological standard IEEE std-145, in which a number of new terms have appeared for the receiving mode of active antennas. It has been shown in the work that the equivalent circuit with parameters determined by noise is also suitable for harmonic signals, which makes it possible to measure the noise temperature taking into account the ambient conditions (at the facility). Since in the ASC it is impossible to change the temperature within significant limits, one measurement is carried out in the chamber, and the second one – at the stand for measuring the power of noise in the direction of the “cold” sky, which was created at JSC “V. Tikhomirov Scientific Research Institute of Instrument Design” in the course of research. The possibility of measurements outside the ASC is justified by the fact that the antennas under test have highly directional radiation patterns and low side lobes. Before performing measurements at the stand, the interference environment was assessed. It turned out that there was no industrial interference in the X-range, but the effect of thermal radiation from the earth was significant. To reduce it, a pyramidal horn screen covered with brass mesh was used. Using the P6-23A antenna and LNA, with known values of the gain and noise, the brightness temperature of the “cold” sky area was measured, which was 14 K. After measuring the noise temperature, the system noise figure is calculated. The experience of using this method shows that it gives an acceptable accuracy when measuring the noise parameters of the AESA with a noise figure of less than 5. The method allows one to compare the characteristics of single-channel and multichannel, as well as domestic and foreign systems.

Sinani A.I., Gridnev V.I. Method for measuring the noise coefficient and noise temperature of AESA in accordance with IEEE standards. Antennas. 2021. № 5. P. 37–45. DOI: https://doi.org/10.18127/j03209601-202105-04 (in Russian)

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