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          the frequency coverage of the GMRT ar- ray was chosen to go from wavelengths of about 20 cm (1500 MHz) to about 2 m (around 150 MHz). To build the GMRT, the group shifted headquarters to Pune and set up the National Centre for Radio Astrophysics (NCRA).
After completion of acquisition of the land in 1990, work on the construc- tion of the GMRT started in 1991, and the first antenna was erected in 1993. Construction of all the 30 antennas was completed by 1995, even as construc- tion and commissioning activities for the different receiver systems continued alongside. Regular astronomical ob- servations started in 1997, and the first publication of results from the GMRT in an international journal happened in 1999. In October 2001, the GMRT was formally declared an international facility, available for use by astronomers from all over the world.
In the process of its indigenous de- sign and construction, the GMRT pio- neered quite a few new and innovative ideas, while overcoming some signifi- cant technological challenges. It was one of the first radio astronomy obser- vatories to replace radio communica- tion links with optical fibre technology to connect the antennas in the array to the central processing facility, a feature that is now almost routine in all modern radio observatories. It was also one of the first interferometric array telescopes to also have a dedicated phased array mode to support observations of com- pact objects like pulsars. The design of the GMRT employed innovative ideas like SMART (Stretched Mesh Attached to Rope Trusses) to build very large fully
National Centre for Radio Astrophysics, Pune, with a few of the GMRT antennas in the background
38 SCIENCE INDIA APRIL, 2021
steerable antennas (45 metres in diam- eter) that are very light (only about 100 tons) and hence very economical, while still providing the required accuracy and efficiency.
The design of the electronics for the GMRT was very challenging, all the way from the radio frequency front-end electronics at each antenna, to the back- end digital signal processing system at the central receiver building; but the in- house teams rose to the challenge and were able to deliver all these systems successfully.
All of this resulted, by the early 2000s, in the creation of the largest and most sensitive low frequency radio telescope in the world — a position that the GMRT has maintained over the years. The next generation at NCRA has further enhanced the capabilities of the GMRT with a major technological upgrade carried out during 2012 - 2018 that will keep it on the forefront on the
global scene.
Over the years, the GMRT has
seen users from more than 40 different countries carry out a range of interest- ing experiments. The competition for observing time on the GMRT is tough, and only the best science proposals get accepted by the review committee. This exemplifies how much the GMRT is sought after by the national and inter- national community for cutting-edge exploration of the Universe and how it has built up its reputation and trust over the years.
The GMRT has produced several new and interesting scientific results and discoveries in more than 20 years of its operation. Presently, around 40-50 pa- pers based on data from the GMRT are published in international journals every year. The range of science addressed is vast, covering many diverse topics: the Sun, radio stars, as well as exotic neu- tron stars (called pulsars); supernova
         Images Courtesy: National Centre for Radio Astrophysics






















































































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