The Tianlai Dish Pathfinder Array: design, operation and performance of
  a prototype transit radio interferometer
  The Tianlai Dish Pathfinder Array is a radio interferometer designed to test
techniques for 21~cm intensity mapping in the post-reionization universe as a
means for measuring large-scale cosmic structure. It performs drift scans of
the sky at constant declination. We describe the design, calibration, noise
level, and stability of this instrument based on the analysis of about $\sim 5
\%$ of 6,200 hours of on-sky observations through October, 2019. Beam pattern
determinations using drones and the transit of bright sources are in good
agreement, and compatible with electromagnetic simulations. Combining all the
baselines, we make maps around bright sources and show that the array behaves
as expected. A few hundred hours of observations at different declinations have
been used to study the array geometry and pointing imperfections, as well as
the instrument noise behaviour. We show that the system temperature is below
80~K for most feed antennas, and that noise fluctuations decrease as expected
with integration time, at least up to a few hundred seconds. Analysis of long
integrations, from 10 nights of observations of the North Celestial Pole,
yielded visibilities with amplitudes of 20-30~mK, consistent with the expected
signal from the NCP radio sky with $<10\,$mK precision for $1 ~\mathrm{MHz}
\times 1~ \mathrm{min}$ binning. Hi-pass filtering the spectra to remove smooth
spectrum signal yields a residual consistent with zero signal at the $0.5\,$mK
level.
