Originally posted by Jagan:
Kapils picture of the HHNN radar - HHNN derives from 'Haan Haan - Nah Nah' from the movement of the two dishes on the radar unit.
No idea as to the model and type - I am only guessing that it is used by the ATC to judge the approach patern of the incoming aircraft (correct range - altitude during approach).
http://www.bharat-rakshak.com/Temp/HHNN.jpg
The radar under question is "Precision Control Approach" radar used for talking down a pilot to land in non VFR flight regiem. It can bring down a pilot to correct approach and landing in zero visbility. Unlike ILS (Instrument Landing System) or ALS that require a specialized instrument in the cockpit, this does not require anything more than a R/T.
Almost all IAF bases have this. Most combat planes depend on it. ALS is not yet on any Indian airport and the ILS can only bring down the plane to 30' decision altitude. PCAR provide similar or slightly better decision thereshold.
The Yes-Yes/No-No is due to the classical beam scanning pattern required for accurate angular position sensing in Elevation and Azimutal plane.