Which type of tracking RADAR has no detectable scan rate, uses 1 RF beam, and can only track one target at a time?

Monopulse radar is characterized by its ability to determine the angle of a target using a single pulse of RF energy. This system employs a unique method where it compares multiple signals received nearly simultaneously rather than scanning across the target location. As a result, it does not have a detectable scan rate like other radar systems that rely on rotating or steering their beams over time.

This instantaneous processing allows monopulse radar to precisely track one target at a time while maintaining high accuracy. The use of only one RF beam is integral to its operation; rather than sweeping the beam to gather data from different angles, it simultaneously processes information from its multiple input channels to establish target position quickly and effectively.

In contrast, the other types of tracking radar include methods that either involve scanning over a certain area or tracking multiple targets, which do not fit the description provided in the question.