Precision Calibration of Radio Interferometers Using Redundant Baselines
  Growing interest in 21 cm tomography has led to the design and construction
of broadband radio interferometers with low noise, moderate angular resolution,
high spectral resolution, and wide fields of view. With characteristics
somewhat different from traditional radio instruments, these interferometers
may require new calibration techniques in order to reach their design
sensitivities. Self-calibration or redundant calibration techniques that allow
an instrument to be calibrated off complicated sky emission structures are
ideal. In particular, the large number of redundant baselines possessed by
these new instruments makes redundant calibration an especially attractive
option. In this paper, we explore the errors and biases in existing redundant
calibration schemes through simulations, and show how statistical biases can be
eliminated. We also develop a general calibration formalism that includes both
redundant baseline methods and basic point source calibration methods as
special cases, and show how slight deviations from perfect redundancy and
coplanarity can be taken into account.
