  Precision measurement of the beam pattern of an antenna is very important for
many applications. While traditionally such measurement is often made in a
microwave anechoic chamber or at a test range, measurement using an unmanned
aerial vehicle offers a number of advantages: the measurement can be made for
the assembled antenna on site, thus reflecting the actual characteristics of
the antenna of interest, and more importantly, it can be performed for larger
antennas which cannot be steered or easily measured using the anechoic chamber
and test range. Here we report our beam measurement experiment with UAV for a 6
meter dish used in the Tianlai array, which is a radio astronomy experiment.
Due to the dish's small collecting area, calibration with an astronomical
source only allows for determining the antenna beam pattern over a very limited
angular range. We describe in detail the setup of the experiment, the
components of the signal transmitting system, the design of the flight path and
the procedure for data processing. We find the UAV measurement of the beam
pattern agrees very well with the astronomical source measurement in the main
lobe, but the UAV measurement can be extended to the fourth side lobe. The
measured position and width of each lobe also shows good agreement with
electromagnetic field simulation. This UAV-based approach of beam pattern
measurement is flexible and inexpensive, and the technique may also be applied
to other experiments.
