A 3.5 mm coaxial calorimeter

The increasing demand for wide band calibrations of coaxial power sensors has prompted NPL to undertake the development of a 3.5 mm coaxial power standard. The system currently under development uses a twin load dry cell coaxial calorimeter where the objective is to provide calibration over the range 0.1 mW to 10 mW with an uncertainty better than 0.25% from DC to 33 GHz. In the design of the 3.5 mm coaxial calorimeter a number of difficulties have arisen due to the physical dimensions of the lines and the manufacturing tolerances involved. This paper discusses some of these problems and provides a report on the current status of the system.<>