Measurement of Effective Efficiency of Thin-Film Barretter Mount at 10.0 Ghz Using Microcalorimetric Technique Established at Npl, New Delhi

Abstract

Thin-film barretter elements and mounts designed and fabricated at NPL serve as the primary standard of microwave power. This paper describes the techniques used for the accurate measurement of effective efficiency of such barretter mounts at X-band by microcalorimeter system established at NPL because a knowledge of effective efficiency is the basis of accurate measurement of microwave power. The single load microcalorimetric technique involves accurate measurement of bolometric and calorimetric powers by dc substitution technique using self-balancing bridge and other circuitry discussed in the paper. The barretter mount is housed in a double-wall enclosure and is kept in a constant temperature oil bath maintained at 25°C±0.001°C during the course of measurements. Various sources of errors hare been analysed in the paper and the total uncertainty in the effective efficiency achieved is ±0.58%. Data on the measurement of effective efficiency of three mounts developed at NPL which will serve as the primary standard of microwave power at 10.0 GHz are also reported.