Detectors

Abstract

Detectors are transducers which convert an incoming signal into some convenient form which can be observed, recorded, and analyzed. The signal – an electromagnetic wave, has an amplitude and a phase. Both contain information. According to the nature of the electromagnetic wave detectors can be separated into two classes. If only the amplitude is detected, it is an incoherent or direct detector. When both the amplitude and phase are detected, the detector is a coherent one. Coherent detection is not a direct process. In a heterodyne receiver, which is the most common coherent detector, detection is in two stages, with the incoming signal being “mixed” with another signal, and it is the combination of both which is detected.