Noise measurements allow the determination of the four Noise Parameters of a device (transistor).  There are four Noise Parameters which fully describe the noise behaviour of an active or passive device at a given frequency. 

The Noise Parameters are not load depended, they are only affected by Source Impedance. There exist a simple relation between the four Noise Parameters:

NF calculation formula is the following:

• NFLinear = NFMinLinear + ((4 * Rn / Zo) * (Gs – GammaOpt).Mag2 ) / ((1 + GammaOpt).Mag2 * (1 – Gs.Mag2));

This is the equation of a set of isometric circles on the Smith Chart (Noise Circles) for which the value of the Noise Figure is the Level on each circle. This Circle Representation is only possible because the Noise behaviour of transistors is a Small Signal Phenomenon.

Where:

• NFminLinear is the minimum noise figure in linear.
• Rn is the equivalent noise resistance in Ohms
• Gs is the gamma presented to the DUT at the input (in our case by the tuner).
•  GammaOpt is the optimum gamma (ie: gamma source for which the DUT produces the minimum noise figure).
  • Note: Mag2 denotes the magnitude squared.

Wideband Noise Parameters using Passive Tuners