  With 30 antennas and a maximum baseline length of 25 km, the Giant Metrewave
Radio Telescope (GMRT) is the premier low-frequency radio interferometer today.
We have carried out a study of possible expansions of the GMRT, via adding new
antennas and installing focal plane arrays (FPAs), to improve its point-source
sensitivity, surface brightness sensitivity, angular resolution, field of view,
and U-V coverage. We have carried out array configuration studies, aimed at
minimizing the number of new GMRT antennas required to obtain a well-behaved
synthesized beam over a wide range of angular resolutions for full-synthesis
observations. This was done via two approaches, tomographic projection and
random sampling, to identify the optimal locations for the new antennas. We
report results for the optimal locations of the antennas of an expanded array
(the "EGMRT"), consisting of the existing 30 GMRT antennas, 30 new antennas at
short distances, $\leq 2.5$ km from the array centre, and 26 new antennas at
long distances, $\approx 5-25$ km from the array centre. The collecting area
and the field of view of the proposed EGMRT array would be larger by factors
of, respectively, $\approx 3$ and $\approx 30$, than those of the GMRT. Indeed,
the EGMRT continuum sensitivity and survey speed with 550-850 MHz FPAs
installed on the 45 antennas within a distance of $\approx 2.5$ km of the array
centre would be far better than those of any existing interferometer, and
comparable to the sensitivity and survey speed of Phase-1 of the Square
Kilometre Array.
