THE INFLUENCE OF MISMATCHES ON THE RESULTS OF MEASURING THE NOISE TEMPERATURE AND THE EFFECTIVE APERTURE OF ANTENNAS BY RADIO ASTRONOMY METHODS

Abstract

The radio astronomy methods for measuring antenna properties allow to measure noise temperature and effective antennas aperture with high accuracy when the antenna and the standard load are ideally matched in the input of the radiometer. Due to appearance of high-efficiency antennas, the requirements to high-precision measurements of noise temperature and the effective aperture of antennas have increased. The earth methods for measuring those antenna parameters turns out to be insufficient and, in some cases, impossible. In practice, antenna parameters measuring and radioastronomy research with high efficiency convincingly proved that the difficulties in measuring by earth methods are relatively easy to overcome.

As high efficiency antennas and low noise receivers have appeared the requirements to measuring antenna properties with high accuracy have increased. For measuring the parameters of large antennas more than 10 cosmic standard sources are chosen. Among them standard sources Cassiopeia - A, Cygnus - A, Taurus - A, and Virgo – A meet the requirements, that have an aperture of up to 80 m of mirrors. In real systems antenna – radiometer, standard load – radiometer always exist a whole reason leading to power re-reflection. At that, the measure and values are characterized by errors (mismatch errors).

The goal of the work is consideration of errors which are conditioned by mismatch and giving methods to decrease them, which allows to eliminate the influence of mismatches in the measurement results. The influence of mismatch are studied when we measure noise temperature and effective antenna aperture in a system which consists of a noisy signal source plus radiometer. Methods which decrease and fully eliminate the influence of those mismatches in measurement results are proposed.