atténuateur

An attenuator, in electronics and related fields, is a passive device designed to reduce the amplitude of a signal without significantly distorting its waveform. Attenuators are used to protect sensitive equipment, establish proper signal levels for test and measurement, and ensure impedance matching across components and cables. They are commonly specified by their attenuation value, usually expressed in decibels (dB), which indicates the ratio between input and output power or voltage.

Most attenuators in RF, microwave, and audio systems are resistive pad networks that present a defined, consistent impedance at the interface, typically 50 ohms or 75 ohms. The two standard topologies for fixed RF attenuators are the Pi (π) network and the T (ladder) network. Fixed attenuators provide a constant attenuation, while variable attenuators allow adjustment over a specified range. Variable types can be mechanical (rotary or slide) or electronically controlled, using diodes, transistors, or other active elements in combination with resistive pads.

Attenuation is measured as the ratio of output to input, expressed in decibels, or equivalently as a voltage or power ratio. In RF design, engineers also consider return loss and isolation to minimize reflections and crosstalk. In audio engineering, pad attenuators help protect inputs and prevent distortion, while maintaining impedance matching and a consistent tonal character.

Beyond electronics, the term attenuator can describe devices in optical systems, where optical attenuators reduce light power to protect detectors or calibrate dynamic range. See also impedance matching, power combiners, and optical power control.