Self-calibration circuits and routines for low-cost measuring systems

A Low-cost measurement system suited for in situ moisture monitoring of buildings is presented. The system consists of a robust and compact resonant microwave sensor linked to a miniaturized, low-cost vector network analyzer. Several such systems can be controlled by a central monitoring station. The measurement accuracy is enhanced significantly by vectorial self-calibration. To determine the magnitude and the required 360°-phase information, an inexpensive combined gain and 180°-phase detector is used, where the full phase information is obtained by adequately modeling the sensor's and the calibration standards' phase response. Different self-calibration circuits are examined and their suitability is proved by comparative measurements. Finally, the system's performance is tested in a high humidity environment. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 287–293, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23083