What is meant by “stationary mode” in radar operation?

In radar operation, "stationary mode" refers to the situation where the radar unit remains fixed in one location while measuring the speed of moving vehicles. This mode is commonly used by law enforcement to monitor traffic speeds, as it allows for accurate and consistent measurements of speed without the influence of the radar unit's own movement. When the radar is stationary, it can effectively detect and capture the speed of vehicles approaching or passing the unit, providing reliable data for speed enforcement.

The other choices involve different operational modes or states that do not align with the concept of stationary mode. For example, if the radar unit is moving, it introduces variables that complicate speed measurement, leading to inaccurate results. Turning the radar unit off or putting it in sleep mode would not allow for any speed measurement to occur, thus deviating from the principle of capturing speed data.