Phase calibration scheme for a "T" array

It is well known that the phase and amplitude errors in the complex visibil ities observed with a radio interferometer array can be effectively removed making use of closure techniques (Jennison 1958; Rogers et al. 1974; Readh ead & Wilkinson 1978) and redundancy in the length and orientation of basel ine vectors (Ishiguro 1974; Noordam & de Bruyn 1982; Wieringa 1992; Nakajim a et al. 1994). These techniques make use of the fact that most of the erro rs can be ascribed to individual antennas (see Pearson & Readhead 1984 for the details). In this paper a scheme based on these techniques is described for eliminating the phase errors in a T-shaped interferometer array partic ularly those in which the tilting of the antenna beam is done through intro duction of phase/delay gradients across the array.