Application of redundancy calibration to phased arrays and some limitations

In new phased array instruments, a fundamental question is whether the geometrically redundant baselines in a regularly arranged phased array are really redundant. Based on real and simulated data, we demonstrate that for a phased array station, a regular arrangement of station elements is necessary but not sufficient to satisfy redundancy calibration requirements. This is due to the electromagnetic interaction between closely spaced antenna elements which leads to non-identical beams and possibly correlated noise. Each of these deterministic effects introduces a bias on the estimated calibration results. Understanding the nature of these effects has helped us to determine the limits of applicability of redundancy calibration for a given phased array, which are demonstrated in this paper.