The Agilent 8491C is a precision coaxial fixed attenuator specified from DC to 18 GHz with Type-N connectors. The attenuator is available in five fixed attenuation values — 3 dB, 6 dB, 10 dB, 20 dB, and 30 dB — selected at order time via option code. Each unit employs a thin-film resistive element deposited on an alumina substrate, a construction approach that delivers consistent attenuation accuracy and low SWR across the full specified frequency range.

A fixed coaxial attenuator reduces signal amplitude by a calibrated decibel amount while maintaining a controlled 50-ohm impedance environment. The 8491C is applied where signal levels need to be reduced precisely without introducing impedance mismatch — extending the range of sensitive power meters for higher-power measurements, pad-matching badly matched devices to improve system SWR, and reducing power levels presented to sensitive components and instrumentation in test setups from DC through 18 GHz.

Every Agilent 8491C unit moving through ValueTronics is received, inspected, and inventoried at our 20,000 sq ft secure warehouse at 1675 Cambridge Drive in Elgin, Illinois. RF passive components like fixed attenuators rely on calibrated film resistive elements and precision Type-N connector geometry — both of which can be compromised by mishandling at any point in the supply chain. Holding stock, inspection, and order fulfillment under one roof means the attenuator that ships from us has been handled by our team, not passed through a drop-ship pipeline we don't control.

Brand Heritage

The 8491C originated with Hewlett-Packard's test and measurement division, which was spun off as Agilent Technologies in 1999. In 2014, Agilent's electronic measurement business became Keysight Technologies. Units labeled HP, Agilent, or Keysight across this product family trace to the same engineering lineage.

Compare Other Models in This Series

The 8491C is sold as a single model with five attenuation-value options — 3 dB, 6 dB, 10 dB, 20 dB, and 30 dB — selected at order time via the option suffix. All five share the same DC to 18 GHz frequency range, the same Type-N connector geometry, the same thin-film tantalum nitride construction, and the same physical envelope. The variants differ only in the calibrated attenuation value and the corresponding accuracy and SWR specifications at each value.

Because the units are fixed attenuators rather than adjustable, the selection decision is straightforward: choose the option whose attenuation value matches the dB reduction your test setup requires. The accuracy and SWR specifications scale modestly with attenuation value, with the 3 dB unit holding tighter accuracy (±0.3 dB to 12.4 GHz) and the 30 dB unit specified at ±1.0 dB across the band.

Each pre-owned 8491C option listed below is presented as its own product page with condition-matched pricing and availability. Select the attenuation value your application requires — the underlying hardware and connector geometry are identical across the family.

The primary difference across the 8491C family is the calibrated attenuation value and its corresponding accuracy band. The 3 dB unit (Option 003) is specified at ±0.3 dB accuracy from DC to 12.4 GHz and ±0.4 dB from 12.4 to 18 GHz, with SWR of 1.25 maximum from DC to 8 GHz. The 6 dB and 10 dB units (Options 006 and 010) hold ±0.4 dB and ±0.6 dB accuracy respectively to 12.4 GHz with SWR of 1.2 from DC to 8 GHz. The 20 dB and 30 dB units (Options 020 and 030) carry ±0.6 dB and ±1.0 dB accuracy to 12.4 GHz, with the 30 dB unit widening to ±1.0 dB across both accuracy bands.

SWR specifications follow a similar pattern across attenuation values: all units in the 6 dB through 30 dB range hold 1.2 from DC to 8 GHz, 1.3 from 8 to 12.4 GHz, and 1.5 from 12.4 to 18 GHz. The 3 dB unit runs slightly higher SWR — 1.25, 1.35, and 1.5 across those same three bands. Refer to the comparison table that follows for the full accuracy and SWR specifications side by side.

Additional differences in specifications beyond the few shown above are not listed here — see each model's full specifications below.

Product Core & Specifications

About this used unit

• Warranty included
• Functional verification included
• Standard Calibration Upgrade Options: No Calibration Required, NIST Traceable, Z540.1 or ISO 17025 with Data, Z540.3 Guardbanding with Data.
• Note that unnecessary accessories may not be included (contact Test Architect to confirm).

Please review the Manufacturer's Data Sheet to verify published specifications. Feedback on this webpage is always welcome — please reach out to your Test Architect at any time for questions or concerns. Thank you, we truly appreciate you being our customer.