Teaching radiofrequency power measurements

Abstract

A method is here proposed to teach radiofrequency (RF) power measurements to master’s degree students in electronics and communications engineering. Before going into the details of the principle of operation and architecture of power meters (not discussed here) the topic of power measurement is introduced emphasizing the fact that power generators and meters are calibrated to indicate the power delivered to, or absorbed by, a perfect Z0 (e.g. $50 \Omega)$ load. Then, it is discussed what happens when this perfect Z0 load assumption is not satisfied introducing the mismatch correction. The mismatch correction is analyzed in terms of uncertainty governed by the U-shaped probability density function (PDF). The U-shaped PDF gives the opportunity to discuss state-of-knowledge PDFs whose use is ubiquitous in measurement uncertainty estimation. Indeed, such U-shaped PDF is not the result of direct observation of the physical world, it reflects the state of knowledge of the experimenter about the physical phenomenon. These concepts are finally applied to a simple estimation of RF power measurement uncertainty, showing that mismatch is, as frequently occurs in precision power measurements, the dominant contribution to uncertainty.