Progress in the Construction and Testing of the Tianlai Radio
  Interferometers
  The Tianlai Pathfinder is designed to demonstrate the feasibility of using a
wide field of view radio interferometers to map the density of neutral hydrogen
in the Universe after the Epoch of Reionizaton. This approach, called 21~cm
intensity-mapping, promises an inexpensive means for surveying the large-scale
structure of the cosmos. The Tianlai Pathfinder presently consists of an array
of three, 15~m $\times$ 40~m cylinder telescopes and an array of sixteen, 6~m
diameter dish antennas located in a radio-quiet part of western China. The two
types of arrays were chosen to determine the advantages and disadvantages of
each approach. The primary goal of the Pathfinder is to make 3D maps by
surveying neutral hydrogen over large areas of the sky %$20,000 {\rm deg}^2$ in
two different redshift ranges: first at $1.03 > z > 0.78$ ($700 - 800$~MHz) and
later at $0.21 > z > 0.12$ ($1170 - 1270$~MHz). The most significant challenge
to $21$~cm intensity-mapping is the removal of strong foreground radiation that
dwarfs the cosmological signal. It requires exquisite knowledge of the
instrumental response, i.e. calibration. In this paper, we provide an overview
of the status of the Pathfinder and discuss the details of some of the analysis
that we have carried out to measure the beam function of both arrays. We
compare electromagnetic simulations of the arrays to measurements, discuss
measurements of the gain and phase stability of the instrument, and provide a
brief overview of the data processing pipeline.
