Discussion on fundamental issues of NPR measurements

This paper investigates the disagreement that exists between noise power ratio (NPR) measurements and a recently published statement that those measurements always underestimate the real nonlinear in-band distortions. A more fundamental approach to settle this discussion is presented. First, it is shown that nonlinear distortions can be split in different contributions, forming the fundamental parts of the NPR or in-band distortions. Next, measurement techniques are presented to obtain these different contributions.