PULSAR MODES OF GMRT

In the array mode, the GMRT can be used for pulsar observations in 2 ways :
1.Incoherent ( IA ) Mode :
In this mode, the power signals from different antennas are combined to give the final signal for pulsar processing. For addition of signals from N antennas, this mode will give a √N improvement in sensitivity over a single antenna while the array will have a beam width equal to that of a single antenna. This will be useful primarily for large scale pulsar search observations.
2.Coherent or Phased Array ( PA ) Mode :
In this mode, the voltage signals are added to get the final signal for two orthogonal polarisations. It will require proper phasing of the array to exactly compensate the delays and phases of signals from different antennas. This will give a sensitivity of N over a single antenna while the beam width will be much narrower than that of a single antenna. This mode will be used primarily for studies of individual pulsars, including polarimeters.
Besides providing a large effective collecting area for meter-wavelength observations of pulsars, one of special capabilities of the pulsar mode of teh GMRT is the ability to observe simulataneously at two ( and even three ) different wave-bands. This is achieved by grouping the antennas into sub-arrays, each operating at a different frequency, and suitably processing the signals from these.

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