Abstract.
In recent decades, radioholographic methods of antenna measurements
are widely used in the antenna technology and radio astronomy. We consider a
new method of the radioholographic signal recording for RATAN-600 radio
telescope, which does not require any special phase-stabilized instrumentation.
In the method proposed, the reference signal is formed with a radial movement of
the reference element (shield) relative to the whole antenna, while the
interferogram (hologram) is recorded using a conventional radio astronomy
receiver as the feed carriage moves in the direction opposed to that of the
reference shield. We give the scheme and the mathematical description of the
new method of the radioholographic signal recording, as well as the results of
the modeling of the reconstruction of the electrical field amplitude and phase
distribution in the telescope aperture related to the positions of the main
mirror shields. We estimate the characteristics of the source of the
radioholographic signal required in order to provide the necessary degree of
the time and space coherence. We found the optimal relation between the speeds
of movement of the feed carriage and the reference shield, the spatial
resolution a which can be achieved, and the maximum dimension D
of the aperture being measured. According to our estimates, a is not
larger than the size of a single shield, while D is more than 100 m and D = 150-200 m seems to be feasible. We present the first results of the application of the new method to
the measurement of the antenna system “South sector + Flat reflector” of
RATAN-600 radio telescope using the signal from a geostationary Earth satellite
at the wavelength of 2.5 cm and in the autocollimation mode at the
wavelengths of 1.8 cm and 1.0 cm. The repeatability of the performed
radioholographic measurements is characterized by the correlation coefficient
of 0.9 in amplitude and 0.7 in phase (radial position). Yet we estimate the
accuracy of the method to be not better than 0.2 mm RMS, it is limited by
the turbulence of the near-surface atmosphere layer during the daytime. At
night, when the spatial phase variance of the near-surface layer is low, the
expected method accuracy should be no worse than 0.1 mm RMS.
Key words: multielement radiotelescope, active surface, radioholographic
measurements and adjustment.
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