This information is edited from a repost of an acig.org forum post by mrdetonator:
http://www.secretprojects.co.uk/forum/index.php/topic,25.msg59.html#msg59
The Sapfir-23E uses the mono-pulse technique to track a single target.
Such a radar system consists of two parabolic antennas (moving, fixed) and the four-cone T/R element.
In this system, each returning radar pulse provides target pointing information by being focused at the antenna onto a group of four-cone T/R elements.
Tracking Process:
After pushing the "Захват" ("Zachvat") button, the radar performs an additional search in the antenna position where the target has been found.
During this additional search, the scan zone shrinks to ±8º in azimuth and ±52' in elevation.
If the target signal is present, the antenna performs angular tracking of the target and the radar range-finder is switched on.
The range-finder searches for the target in a 9 km range zone.
If the target is within the 9 km zone, the antenna performs range tracking of the target.
The SEI indicator changes its appearance.
It is now showing the crosshair and the circle guidance indicator instead of selection lines (range zone).
The radar is tracking the target.
The tracking principle is based on summing the elevation, azimuth and the reference signal taken from the 4-cone receiver.