Array Configuration

Figure 18.1: GMRT array configuration.

The GMRT has a hybrid configuration, (see Figure 18.1) with 14 of its antennas randomly distributed in a central region ($\sim 1$ km across), called the central square. The distribution of antennas in the central square was deliberately ``randomized'' to avoid grating lobes. The antennas in the central square are labeled as Cnn, with nn going from 00 to 14 (i.e. C00, C01,....C14)<sup>18.1</sup>. The remaining antennas are distributed in a roughly Y shaped configuration, with the length of each arm of the Y being $\sim 14$ km. The maximum baseline length between the extreme arm antennas is $\sim 25$ km. The arms are called the ``East'' ``West'' and ``South'' arms and the antennas in these arms are labeled E01..E06, W01..W06 and S01..S06 for the east, west and south arm respectively.

The central square antennas provide a large number of relatively short baselines. This is very useful for imaging large extended sources, whose visibilities are concentrated near the origin of the UV plane. The arm antennas on the other hand are useful in imaging small sources, where high angular resolution is essential. A single GMRT observation hence yields information on a variety of angular scales.

Footnotes

... C01,....C14)^18.1

The array was originally meant to have 34 antennas, but because of escalating costs, was finally constructed with 30. Consequently some antenna stations do not actually have any antennas in them, resulting in ``missing'' numbers (C07, E01, S05) in the numbering sequence.