Thin-film thermoelectric transducer for measurements of low-level power between 0 and II GHz

The paper describes a thermal convertor mounted in a 50 ¿ coaxial line, which consists of two thin resistance films heated by the electric current being measured, with a high-sensitivity thin-film thermocouple attached to the midpoint of each resistance film to give the temperature rise at that point. Both the heater and the thermocouple are deposited on a substrate and insulated from each other; thus it is described as an `indirectly heated thermocouple¿. The thermocouple is made from n- and p-type germanium films and produces a d.c. output of 1 ¿V at ¿40 dBm power level. The thin-film thermoelectric transducer can be calibrated in terms of d.c. power dissipation, and gives measurements of power in the range ¿40 to +20 dBm with an accuracy of within ±2% at frequencies of 0¿1 GHz. Comparison of the performance of the device with other measuring instruments indicates that it is of acceptable accuracy, even at microwave frequencies up to 11 GHz. Moreover, it was found that measurements of ¿50 dBm were possible by this device provided that effects of the thermal noise and drift of the transducer were eliminated by digital integration and differentiation circuits. Errors arising in these measurements are also discussed.