Linking the Power Scales of Free-Space and Waveguide-Based Electromagnetic Waves
Andreas Steiger, Physikalisch-Technische Bundesanstalt (PTB), Germany
based on a joint work with
Rolf Judaschke, Mathias Kehrt, and Karsten Kuhlmann
Physikalisch-Technische Bundesanstalt (PTB), Germany
Summary: Two independent methods for absolute power measurement of electromagnetic waves are compared in the millimeter wave range. Depending on frequency and wave propagation, electromagnetic power is traced back to the International System of Units (SI) in different ways at National Metrology Institutes (NMIs) such as the PTB in Germany. From microwave to millimeter-wave frequencies, traceability is achieved in coaxial lines and metallic waveguides, and in the terahertz range in free space. Since modern waveguide-based power sensors and free-space power detectors are overlapping with respect to their operating frequency, a comparison of the two independent power scales was performed for the first time in the millimeter-wave range in the WR-10 band (i.e., for frequencies from 75 GHz to 110 GHz).
For this comparison, a special measuring setup has been developed. It consists of a tailor-made, large elliptical mirror which focuses a known radio frequency (RF) power, radiated by a special corrugated horn antenna, into the aperture of a calibrated free-space detector. The experiment confirmed the consistency of the two traceability approaches within their uncertainties.
This proof of equivalence opens the promising possibility of accurately measuring RF power in higher-frequency waveguide bands up to the THz range with the free-space method applied.
Biography: Andreas Steiger received the Diploma degree in physics from the TU Karlsruhe, now KIT in Karlsruhe, Germany, in 1984, and the Dr. rer. nat. degree in physics from the TU Berlin, in Berlin, Germany, in 1993. He joined the Physikalisch-Technische Bundesanstalt (PTB) in Berlin, Germany in 1986 as a research scientist in the field of plasma diagnostics by means of laser spectroscopy. From 2003 to 2008, he was head of the working group radiation sources for radiometry. Since 2009, after the first calibration of a terahertz detector traceable to the International System of Units (SI), he is leading PTB’s working group terahertz radiometry. Large-area pyroelectric detectors with constant spectral responsivity in the entire THz spectral range were developed jointly with a manufacturer. These unique THz detectors were awarded the German Association for Sensor and Measurement Technology (AMA) special Innovation Award 2017 for Young Companies after the absolute THz power of a time-domain spectroscopy (TDS) system was measured for the first time.
Within the scope of his THz standardization activities at the German metrology institute PTB, Dr. Steiger is a founding member of the German VDI/VDE Technical Committee 8.17 “Terahertz Systems”. Its task is to develop first technical guidelines for time- and frequency-resolved THz systems.
Having performed an initial international comparison of spectral responsivity in the THz spectral range at two laser frequencies (2.52 THz and 762 GHz), Dr. Steiger now chairs the Discussion Forum on THz Metrology (CCPR-WG-SP-TG8) at the Bureau International des Poids et Mesures (BIPM).