This is used in air traffic control systems and has an influence on the shape of the elevation pattern of the surveillance antenna.
It is represented in terms of numerical value typically expressed in decibels (dB), starting from zero, indicating that there is no muting and that the radar system is accepting all returns.
STC is due to the corollary of this statement - nearby targets return orders of magnitude more radio signal.
The downside to this approach is that it permanently hides any signal below a certain angle, which for a very long-range system might prevent it from seeing anything near the radar site.
The gain modification is reduced over time, until it reaches zero at some selected distance from the radar site, often on the order of 50 miles (80 km).
This is fine for many applications, like air traffic control, where the targets are large and nearby aircraft are often guided using a local-area radar.