Amplifier Measurements Using Vector Network Analyzers

RF amplifiers are an important part of many RF systems designs and it is often required to make Vector Network Analyzer (VNA) measurements of them to verify function and ensure suitability for the intended application. Measurement of these devices present challenges – among them, the need for a pre-amplifier to produce sufficient drive level for a Power Amplifier (PA), handling of the output power in a way that properly loads the PA without damaging the input port of the VNA, and determining calibration methods to achieve acceptable accuracy.

Additionally, one may want to measure the output impedance of the amplifier while it is being driven with an input signal which excites it to its nominal output level. Output power vs. input power may be measured to determine amplitude linearity. Harmonic distortion, AM to AM, and AM to PM conversion may be analyzed. All these measurements are possible with a VNA, but a proper setup is needed to achieve accurate results.