Measurements on Devices with Very High Noise Figure

Measurements of very high noise figure components are performed for a number of reasons. For instance, in a wide range of applications, devices under test (DUT) are characterized within a complex test setup that includes high losses before or after the low noise DUT. In case of high frequencies, the switch matrix with complex signal routing and cables might have a very high loss. In other cases, the device might be embedded in a test setup where direct access is physically impossible, on-wafer probing is one example for this case. Using conventional measurement equipment, the noise figure measurement of such a device is very unstable if not impossible at all.

This application note describes a technique to perform the noise figure measurement on lossy devices like attenuators, or on devices embedded into in test setups with high loss in front of the low noise amplifiers. The R&S FSW-K30 noise figure measurement application performs this important measurement with a signal and spectrum analyzer using the Y-factor method. Key for this technique is a modified noise source with high level noise output signal that stimulates the device under test, and a sensitive spectrum analyzer that captures the signal from the device. Besides evaluating the noise figure, amplitude gain or Y-factor, the measurement application allows to measure the ENR of the modified noise source this allowing precise measurements.