A Coaxial Calorimeter for Use as a Microwave Power Standard

A coaxial calorimeter has been built for use in the comparison of power at high frequencies with dc resistance and voltage standards. The temperature rise of the metal jacket of a 50-ohm coaxial termination is measured with a thermopile when a known level of dc power is fed into the calorimeter. The high-frequency sensitivity of the calorimeter is obtained by modifying the dc sensitivity for: 1) Input VSWR of the calorimeter, 2) Attenuation of a 6-inch length of thermally insulating input coaxial line, 3) The effect of current distribution in the load. The accuracy is estimated at better than ±1 per cent below 4 Gc/s with the largest errors due to the input VSWR of the calorimeter.