Y-Factor vs. Cold-Sourced Noise Figure Measurement of RF/Microwave LNAS

There are several RF noise figure measurement methods for RF microwave, and millimeter-wave low noise amplifiers (LNAs), each with a wide number of options, instruments, and techniques. In a recent Tech Brief, Erzia reviews how we came up with an approach using standard laboratory equipment that can easily be followed by trained personnel working at higher frequencies to obtain optimal NF data.

Y-Factor Technique for RF Noise Figure Measurement 

First, we explored the Y-Factor technique, one of the most widely used RF noise figure measurement methods for evaluating the noise figure of an RF device. Its relative simplicity and fast calibration make this a preferred technique when measuring the noise figures of components in systems with relatively high NF values, and/or when extreme levels of accuracy are not critical. 

However, within RF noise figure measurement methods, the Y-factor approach has limitations. The effect of the device under test (DUT) input matching (often due to inconsistent LNA values) and reduced accuracy at higher frequencies make it a poor candidate for testing noise above 18 GHz (K-band).

Cold-Source Method for High-Frequency RF Noise Figure Measurement

At K-band and above, Erzia has determined that the preferred option among RF noise figure measurement methods is the cold-source technique. While it requires the use of a power meter for maximum accuracy at the calibration step (as opposed to a noise source), the result is optimized matching of the calibration device and the DUT.

The cold-source method, using a power meter during calibration and a source-correction technique, provides incredibly accurate data on devices that operate at both narrow and wide bands above 18 GHz. This makes it a critical method within advanced RF noise figure measurement methods for high-frequency applications.

Trade-Offs Between RF Noise Figure Measurement Methods

 The drawbacks of the cold-source technique, however, are that calibration is slower, and the equipment cost is significantly higher than the Y-factor method.

Summary of RF noise figure measurement methods:

• Y-Factor method:

  • Fast calibration
  • Lower cost
  • Suitable for lower frequencies and moderate accuracy requirements

• Cold-Source Method:

  • Higher accuracy at K-band and above
  • Better DUT matching
  • Slower calibration and higher equipment cost

The advantages and disadvantages of each are compared in this chart for reference and consideration in your own RF/microwave applications:

To learn more about RF noise figure measurement methods for K/Ka-band LNAs,, download our Tech Brief:
“Accurate Noise Figure Measurement in ERZIA K/Ka-Band Low Noise Amplifiers for Satcom Applications”