Mechanical and electronic imperfections can result into polarization leakage in individual antennas of a radio interferometer. Such leakages manifest themselves as closure errors even in co-polar visibility measurements of unpolarized sources. Towards the very end of this dissertation, work was done to develope and test a method for the computation of polarization leakage for radio interferometric telescopes using only the nominally co-polar visibilities. This chapter describes the work done in this direction (Bhatnagar & Nityananda, in press).