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The Tianlai Pathfinder is designed to demonstrate the feasibility of using awide field of view radio interferometers to map the density of neutral hydrogenin the Universe after the Epoch of Reionizaton. This approach, called 21~cmintensity-mapping, promises an inexpensive means for surveying the large-scalestructure of the cosmos. The Tianlai Pathfinder presently consists of an arrayof three, 15~m $\times$ 40~m cylinder telescopes and an array of sixteen, 6~mdiameter dish antennas located in a radio-quiet part of western China. The twotypes of arrays were chosen to determine the advantages and disadvantages ofeach approach. The primary goal of the Pathfinder is to make 3D maps bysurveying neutral hydrogen over large areas of the sky %$20,000 {\rm deg}^2$ intwo different redshift ranges: first at $1.03 > z > 0.78$ ($700 - 800$~MHz) andlater at $0.21 > z > 0.12$ ($1170 - 1270$~MHz). The most significant challengeto $21$~cm intensity-mapping is the removal of strong foreground radiation thatdwarfs the cosmological signal. It requires exquisite knowledge of theinstrumental response, i.e. calibration. In this paper, we provide an overviewof the status of the Pathfinder and discuss the details of some of the analysisthat we have carried out to measure the beam function of both arrays. Wecompare electromagnetic simulations of the arrays to measurements, discussmeasurements of the gain and phase stability of the instrument, and provide abrief overview of the data processing pipeline.

Progress in the Construction and Testing of the Tianlai Radio Interferometers