  We provide the first in situ measurements of antenna element (tile) beam
shapes of the Murchison Widefield Array (MWA), a low radio-frequency
interferometer and an SKA precursor. Most current MWA processing pipelines use
an assumed beam shape, errors in which can cause absolute and relative flux
density errors, as well as polarisation 'leakage'. This makes understanding the
primary beam of paramount importance, especially for sensitive experiments such
as a measurement of the 21 cm line from the epoch of reionisation (EoR). The
calibration requirements for measuring the EoR 21 cm line are so extreme that
tile to tile beam variations may affect our ability to make a detection.
Measuring the primary beam shape from visibilities alone is challenging, as
multiple instrumental, atmospheric, and astrophysical factors contribute to
uncertainties in the data. Building on the methods of Neben et al. (2015), we
tap directly into the receiving elements of the MWA before any digitisation or
correlation of the signal. Using ORBCOMM satellite passes we are able to
produce all-sky maps for 4 separate tiles in the XX polarisation. We find good
agreement with the cutting-edge 'fully' embedded element (FEE) model of
Sokolowski et al. (2017), and observe that the MWA beamformers consistently
recreate beam shapes to within ~1dB in the reliable areas of our beam maps. We
also clearly observe the effects of a missing dipole from a tile in one of our
beam maps, and show that the FEE model is able to reproduce this modified beam
shape. We end by motivating and outlining additional onsite experiments to
further constrain the primary beam behaviour.
