Abstract
The Ooty Radio Telescope (ORT), one of the largest in the world, operating at 327 MHz since 1970, has been upgraded with a new feed system. It consists of a phased array of 1056 array of dipoles each followed by a GaAsFET low noise amplifier (LNA) and a four bit PIN diode microstripline phase shifter behind each dipole. This paper describes the new feed installed along the focal line of the 530m long and 30m wide parabolic cylindrical reflector of the ORT. The antenna beam of ORT is steered in the north- south direction by suitably phasing this dipole array and in the east-west direction by mechanical rotation about its axis. Adding a LNA behind each dipole has compensated for the loss in the transmission through the phase shifter, thus drastically reducing the system temperature to less than 150K, compared to 350K for the earlier feeds. The new feed has thus brought about an improvement in the sensitivity of the ORT by a factor over three compared to the best ever of the previous feeds. It was installed in early 1992. With such high sensitivity of the feed system, the large collecting area of ORT is being exploited fully for the studies of astrophysical phenomena such as pulsars, solar wind, recombination lines and protogalaxy. It will also be used for Very Long Baseline Interferometry (VLBI) networks.
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