What are RF Step Attenuators?

RF Step Attenuators are a gang of RF fixed attenuators with an RF path that can selectively pass through any one of a series of the fixed attenuators or not. In this way, various attenuation levels can be reached by switching the combination of the RF step attenuators. Hence, RF step attenuators are a combination of toggle switches, attenuators, and interconnect. The most common type of RF step attenuators are coaxial RF step attenuators, where the coaxial input and output allows for common interconnection among a variety of test and measurement equipment as well as other RF systems

Key RF Attenuator Performance Specifications

Frequency range [Hz]
VSWR [ratio]
Insertion loss [dB] *lowest attenuation value
Attenuation value(s) [dB]
Step size [dB]
Step type [toggle etc]
Impedance [Ohms]
Velocity of propagation [%c]
Power handling (CW, peak) [Watts]
Attenuation accuracy [+/-dB]
Connector type 1 and 2
Temperature range of operation [deg C]

There are a few types of RF step attenuator switch control mechanisms. The most basic type is a series of RF fixed attenuators connected to toggle switches that either have the RF path pass through the fixed attenuator or an impedance matched interconnect to the next step. There are also push button type RF step attenuators, where a button, often labeled with the fixed attenuation activated by the button, can simply be pressed to set the attenuation level. Another type uses rotary switches to switch between the various attenuation levels. In this case, these rotary step attenuators are sometimes cascaded with other rotary step attenuators of different attenuation levels to allow for much higher and higher resolution step attenuation. For instance, a rotary step attenuator with a 1 to 10 dB step attenuator followed by a 0.1 to 1 dB step attenuator could be used to reach any value to 0.1 dB decimal places from 1.1 to 11 dB. Furthermore, additional rotary step attenuators can be added to increase the attenuation range further. Following the previous example, a 0.1 dB to 1 dB, a 1 dB to 10 dB, and a 10 dB to 100 dB step attenuator cascade can be arranged to allow for attenuation values from 11.1 dB to 111 dB.

With RF step attenuators, each additional step range comes with additional insertion loss. Hence, there is a practical limitation on the number of step attenuations and the minimum insertion loss value.