tokens: both approaches, was carried out by restricting the EGMRT antenna locations to lie within the central square. Further, we included only the 14 GMRT central square antennas as ‘fixed’ antennas in the optimization. In the tomographic projection method, beginning with the above fixed GMRT antennas, we add N new antennas to the array, starting with N = 1, and increasing the number of new antennas by one at each iteration. For each value of N , we carried out the tomographic projection optimization for 100 random initial conditions for the new antenna locations, and evaluated the final Residual RMS for each of the 100 realizations. We then chose the realization with the lowest Residual RMS as the optimal configuration for the N new antennas. This minimum Residual RMS was saved, along with the locations of the new antennas, and the process repeated for ( N + 1) new antennas. The Residual RMS initially declines steeply with each new added antenna, as the UV coverage approaches a 2D Gaussian UV distribution. However, beyond some number of new antennas, there is no significant decrease in the Residual RMS, i.e. improvement in the UV coverage, on adding more antennas. We fixed the number of new antennas to the number above which the Residual RMS does not change by more than ≈10 per cent with the addition of further new antennas. In the random-sampling method, we again add N new antennas to the array, starting with N = 1, and increasing the number of new antennas by one at each iteration. However, here we randomly assign the new antennas to available cells in the GMRT central square, keeping the locations of the existing GMRT antennas fixed. We then evaluate the Residual RMS for the configuration, comparing the UV coverage of the configuration with the ‘ideal’ 2D Gaussian of FWHM = 0.5 km. We carry out this random assignment process 10 4 times for each value of N , and determine the minimum Residual RMS for the 10 4 evaluated configurations. This minimum Residual RMS is then stored, again along with the locations of the new antennas, and the process is repeated, by adding ( N + 1) antennas. We find a pattern similar to that seen in the tomographic projection approach, i.e. that the Residual RMS initially declines steeply with each added antenna, but, beyond some number of new antennas, does not decrease significantly on adding more antennas. Again, the number of new antennas is then fixed to the number above which the Residual RMS does not change by more than ≈10 per cent with the addition of further new antennas. As noted earlier, the above process was carried out independently for four declinations, δ = −30°, +30°, and +60°. Fig. 3(A) shows the Residual RMS plotted against the number of antennas for the four different declinations, with the results obtained via the tomographic projection method. The dashed vertical line indicates eight added antennas, beyond which the Residual RMS improves only slowly with additional antennas (for all four
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