Linking the Power Scales of Free-Space and Waveguide-Based Electromagnetic Waves

Two independent methods of absolute power measurement of electromagnetic waves are compared in the millimeter-wave range. At the National Metrology Institutes (NMIs), dependent on frequency and wave propagation, electromagnetic power is differently traced back to the International System of Units (SI), i.e., from microwave up to millimeter-wave frequencies in coaxial lines and metallic waveguides and terahertz frequencies in free space. As state-of-the-art waveguide-based power sensors and free-space power detectors are overlapping with respect to their operating frequency, for the first time, a comparison of both independent power scales has been carried out in the millimeter-wave range. The experiment verified the consistency of both traceability approaches within their uncertainties.