ABSTRACT
The phase-shift measurement (or phase-detection) ranging technique involves continuous-wave (CW) transmission as opposed to the short-duration pulsed outputs used in the time-of-flight systems discussed in Chapter 5. (The transmission of short pulses may also be used if synchronized to a continuouswave reference against which the phase of the returning signal is measured.) One advantage of continuous-wave systems over pulsed methods is the ability to measure the direction and velocity of a moving target, in addition to its range. In 1842, an Austrian by the name of Johann Doppler published a paper describing what has since become known as the Doppler effect: the frequency of an energy wave reflected from an object in motion is a function of the relative velocity between the object and the observer. This subject will be discussed in more detail in Chapter 8.
