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RF Attenuator Fundamentals

Attenuators are fundamental components of RF and Microwave circuits and systems. Often found in virtually every RF application, attenuators play a vital role in receivers, transmitters, and test and measurement systems.

Attenuators simply decrease the wanted or unwanted signal strength along a signal path. They can be used to decrease the output signal of a device-under-test before a sensitive test and measurement receiver, to ensure a more conformal impedance match, or to ensure precise control of the signal amplitude at the output of a transmitter. The attenuation level of a device—the amount of signal power/voltage lost through the device—is commonly measured in either decibels (dB) or as a voltage ratio.

The most common attenuators are broadband attenuators. But, some attenuator types and technologies may have frequency dependant performance and limitations. Though terminations also reduce the signal strength at the load of a system, attenuators differ from terminations as they are in-line to the signal path.

Attenuators are based on passive resistors, absorptive material/techniques, PIN diodes, or field-effect transistor (FET) technologies. Additionally, attenuators can be developed from coaxial transmission line, stripline, surface mount, or even waveguide interconnect technologies. The performance and physical properties of these different technologies vary widely. The quality of construction and costs also contribute to the range in performance, thermal, and physical properties.

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