  This paper discusses an outdoor test facility for the noise characterization
of active antenna arrays, using measurement results of array noise temperatures
in the order of 50 K for a number of small aperture arrays. The measurement
results are obtained by a Y-factor method with hot and a cold noise sources,
with an absorber at room temperature as the hot load and the cold sky as the
cold load. The effect of shielding the arrays by the test facility, with
respect to noise and RFI from the environment, will also be discussed.
