Indian scientists have carried out pioneering research work in the fields of astronomy and astrophysics, solar/interplanetary medium, earth's upper atmosphere/ionosphere, aeronomy/middle atmosphere and weather/climate phenomena. The nationally coordinated Indian Middle Atmosphere Programme (IMAP) was implemented during the period 1982-89 with well focussed campaign experiments with ground based, balloon, rocket and satellite based techniques. The IMAP programme led to the decision to conduct in-depth studies of atmosphericdynamical phenomena by developing a versatile ground based radar technique...

...The MST Radar  is a state of the art instrument capable of providing estimates of atmospheric parameters with very high resolution on a continuous basis which are essential in the study of different dynamical processes in the atmosphere. It is an important research tool in the investigation of prevailing winds, waves ( including gravity waves) turbulence, and atmospheric stability & other mesoscale phenomena . A reliable three dimensional model of the atmosphere over the low latitudes improves our understanding of the climatic and weather variations...

Establishment of NMRF

Attaching great importance to the scientific utilisation of the Indian MST Radar, the Government of India decided to create an autonomous Scientific Society called the National MST Radar Facility (NMRF). This society is affliated to the Department Of Space. The NMRF was registered on January 11, 1993 under the Indian Societies Act 1860.
This society is administered by a Governing Council under the chairmanship of Dr. K. Kasturirangan, Secretary DOS with, Director , NMRF as the member secretary . The present Director of NMRF is Prof D. Narayan Rao .The Governing Council consists of other eminent scientists, representatives of the National Laboratories and some of the funding agencies.The Governing Council sets broad policy guidelines to ensure the effective scientific utilisation of the facility, supported by a Scientific Advisory Commitee & a Finance Commitee.

Location Of NMRF 

The scientific requirements dictated that the Indian MST Radar should be located preferably below 15 degrees North latitude. Hence after careful consideration of the various constraints, a site at Gadanki Village, near the temple town of Tirupati in the Chitoor district of Andhra Pradesh was selected for locating the Indian MST Radar . NMRF is located off the Chitoor -Tirupati main road in a picturesque landscape spreading over an area of about 42 acres. Regular train and bus services are operated between Tirupati and Bangalore/Madras. On request NMRF may provide transport between Tirupati and Gadanki. 

SOURCE: The National MST Radar Facility (NMRF)
..

Like the HAARP Facility in Alaska, this is the best resolution available on Google Earth

The Indian MST Radar is a highly sensitive VHF phased array radar operating at 53 MHz with an peak power aperture product of 3 x 1010 Wm 2 .The system design specifications, including that of the intermediate stage of ST mode , are presented below :
The phased array consists of 1024 crossed three-element Yagi antennas occupying an area of 130m x 130m. It generates a radiation pattern with a main beam of 3 deg , gain of 36 dB and a side lobe level of -20 dB.The main beam can, in principle, be positioned at 82 different look angles in NS and EW plane.

A total transmiting power of 2.5 MW ( peak ) is provided by 32 transmitters ranging in power from 20 kW to 120 kW, each feeding a subarray of 32 Yagis. To achieve the desired low side lobe level to the adiation pattern, the power is tapered across the array according to a modified Taylor distribution. The required power taper is accomplished in one principal direction by the differential powers of the transmitters and in the other direction by the series feed network .

The transmitters can operate up to a duty cycle of 2.5%, limiting the total average power to about 60 kW. It is possible to transmit both coded and uncoded pulses with PRF in the range 62.5 Hz-8 kHz.The uncoded / coded pulses can be varied in pulse width from 1 to 64 microsec.

A phase coherent reciever with quadrature channels , having an overall gain of 110 dB , a dynamic range of 70 dB , and a bandwidth matched to the baud length of the coded pulse, detects the weak back-scattered signal. The switching of the antenna array between transmitter and receiver is accomplised by T/R switches of hybrid coupler and PIN diode design. A frequency synthesizer using a master oscillator with stability better than one part in 1010 ( short term ) provides transmitter, carrier and modulation as well as receiver injection signals, rendering the system phase coherent . The quadrature outputs of the receiver are given to a pre - processor unit consisting of two identical channels of A/D convertor ( ADC ), decoder and coherent integrator. The ADC is of 14-bit resolution to match the dynamic range ( 70 dB ) of the receiver.The analog signal in each channel is sampled and converted to digital at the rate of 1 MHz.
The decoding operation essentially involves correlating the incoming data from the ADC with the replica of the transmitted code. It is implemented by means of a 16-bit 64-tap correlator/transversal filter chip (Two IMS A 100 in cascaded mode). The entire data acqusition and signal processing is realized with digital signal processing chips. ADSP21060 DSP processer with 14-bit ADC is used for the data aqusition and 6 DSP processer base card is used for signal processing purpose. The entire system works in real time and housed in a window NT based Work station. The total computational power of DSP system is 800 MFLOPS in its peak perfomance. The radar operates under instructions from a PC-AT based radar controller which executes an experiment according to the program given in the form of an experiment specification file ( ESF ).

Specifications of Indian MST Radar

Block diagram of Indian MST Radar

SOURCE: ISRO NMRF