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What is the Noise Figure accuracy specification for measuring “my device”?

Keysight cannot provide an "accuracy specification" for noise figure measurements of your device, however there is a tool available that you can use to calculate the measurement uncertainty.

The following example demonstrates how you can calculate the measurement uncertainty of a 40 GHz amplifier measurement using the N8975A, 26.5 GHz NFA Series Noise Figure Analyzer and an N8975AZ-K50, 50 GHz Block Downconverter by using Keysight's web-based noise figure uncertainty calculator at

This calculator can be used for any of our spectrum analyzer based noise figure solutions. Please note there are several application notes that should be used as reference material for making NF measurements. Links to this and other useful information can be found below.

The actual uncertainty of the noise figure measurement depends on the parameters of the device being tested as well as the characteristics of the measurement system being used to make the measurement. These parameters include the following:

  1. DUT Parameters
  • Expected DUT Gain
  • Expected Noise Figure
  • DUT Input and Output Match

   2.  Noise Source Parameters

  • ENR Uncertainty
  • Noise Source Match

   3.  Instrument Parameters

  • Instrument Noise Figure Uncertainty
  • Instrument Gain Uncertainty
  • Instrument's own Noise Figure
  • Instrument Input Match

   4.  External Preamplifier Parameters (if used)

  • External Preamplifier Gain
  • External Preamplifier Input Match

Here is a sample calculation using the noise figure uncertainty calculator. Please note some assumptions had to be made about the D.U.T. gain and match, noise source uncertainty, and the match of the block downconverter. The assumptions made about the source and the block downconverter are accurate but the assumptions made about the D.U.T. are just a guess. The assumption made that the input SWR of 2.5 for the block downconverter based on some internal information provided about similar block downconverters provided by the 3rd party vendor. For the purpose of this example, an N8975A, 26.5 GHz NFA, 346C-K01, 50 GHz noise source, and an N8975AZ-K50, 50 GHz block downconverter were used.

Note:  The "Instrument Noise Fig, NF2 (dB)" term is from the N8975AZ-K50 block downconverter specification, and the "Inst. Noise Fig Uncert. (+/-dB)" and "Gain Uncertainty (+/-dB)" terms are from the N8975A Noise Figure Analyzer data sheet.  (Refer to the calibration reports for your actual devices and instrumentation for more accurate instrument and device uncertainties to enter into the calculator.  You can also measure the actual match of your devices with a Network Analyzer to obtain more accurate match information.)

Noise Figure Calculator Data Entry Screen


NF Data Entry Screen

Noise Figure Calculator Uncertainty Results Screen


NF Results Screen

For more information about making Noise Figure measurements you can refer to the following documents: