Which of the following is a type of microwave detector?

The frequency-modulated continuous wave (FMCW) is a type of microwave detector known for its ability to detect and measure the distance of objects through the use of a frequency-modulated signal. This technology works by emitting a signal that varies in frequency over time and then analyzing the returned signal to determine distance. It offers advantages such as improved accuracy and the capability to operate effectively in diverse conditions, making it particularly suitable for applications like traffic detection and management.

In contrast, other options like amplitude-modulated continuous wave (AMCW) are primarily focused on amplitude variations rather than frequency variations, which limits their functionality in certain detection scenarios. Pulse-width modulation (PWM) and digital modulation involve techniques related to encoding information rather than specifically detecting the presence or distance of objects, making them less applicable as microwave detectors in the context outlined. Thus, FMCW stands out as a specialized and effective method for microwave detection.