Characterizing power amplifier static AM/PM with spectrum analyzer measurements

Power amplifier (PA) behavior and distortion analysis requires the characterization of the PA nonlinear static input-output relationship, usually evaluated through the input amplitude to output amplitude, AM/AM, response. However, the PA input amplitude to output phase shift, AM/PM, behavior has an equivalent impact on distortion generation, and so it must be also measured. This can be obtained by vector signal analyzer (VSA) measurements, an expensive equipment that is not usually available at most microwave PA design laboratories. In this manuscript we demonstrate that both the AM/AM and AM/PM PA characterizations can be effectively performed from the spectral magnitude of continuous-wave, CW, and two-tone tests, not requiring any direct measurement of signal phase. This is very important since it enables the full AM/AM and AM/PM PA characterization to be performed with a typical spectrum analyzer, a common equipment in all RF and microwave laboratories.