The Absolute Determination of Near Millimetre Wave Power in Free Space

An absolute power measuring facility for the calibration of free-field power meters at near millimetre wavelengths, is described. Accuracy is two percent at the one milliwatt level, a tenfold improvement over present free field methods. The measuring principle is based on a photo-acoustic cell and is absolutely calibrated by substitution of low frequency a.c. power. This calibration facility is available at the National Physical Laboratory, Teddington, England.