RF circuits useful for lowering signal amplitude by absorbing a fixed amount of RF energy are called fixed RF attenuators. These devices are also used for dissipating excess signal energy, enhancing impedance matching between two components/devices by lowering the standing waves created by impedance mismatch, and as part of more complex electronic protection for sensitive components. The main use of fixed RF attenuators is for signal level conditioning, typically when the range of input signal energy is known and is greater than that of the desired signal energy at the port attached to the attenuator.
An RF fixed attenuator is specified as a signal attenuation value over a range of frequencies. These attenuators are simple resistive circuits designed to present a nominal impedance at the input and output and may be balanced or unbalanced depending on if the attenuator is meant for balanced transmission lines or balanced transmission lines. Attenuators are made for a variety of different interconnect types, such as coaxial, twisted pair, waveguide, surface mount technology (SMT) as part of planar transmission lines/waveguide (microstrip, stripline, coplanar waveguides, etc.), or as bare die. RF fixed attenuators for waveguide are fabricated differently than coaxial or SMT attenuators with discrete resistive components, often as a waveguide packed with RF absorbing materials.
Key Fixed RF Attenuator Performance Specifications
- Frequency range [Hz]
- VSWR [ratio]
- Insertion loss [dB] *lowest attenuation value
- Attenuation value(s) [dB] *sometimes given over frequency
- Impedance [Ohms]
- Velocity of propagation [%c]
- Power handling (CW, peak) [Watts]
- Attenuation accuracy [+/-dB]
- Interconnect (Connector type 1 and 2 for coaxial, waveguide flange type for waveguide, SMT, etc.)
- Temperature range of operation [deg C]
- Thermal management (heat sink capability, active/passive)
RF attenuators are typically selected based on their attenuation level, frequency range, and power handling capability. In some applications the accuracy of the attenuation is very important, such as test/measurement, metrology, and precision sensing. In other applications, the power handling is most critical. RF fixed attenuators made for high RF power handling applications often include passive or active thermal management. This can be as simple as a metallic housing, a heatsink, a heatsink with active air cooling, or even as a liquid cooled system.
Fixed RF attenuators are foundational elements used throughout the RF industry for test and measurement, sensing, communications, and in virtually every environment RF technology is used. There are RF fixed attenuators available that meet the wide variety of automotive, aerospace, space, naval/maritime,