Abstract :
The paper describes a simple standard technique, using thin metallic films sputtered on mica, for the direct measurement of powers in the range 1¿100 mW. The experiments were carried out at a frequency of 10 Gc/s (wavelength 3cm), but the methods used are of general application in rectangular waveguides. The absorbing films consisted of a platinum deposit, of the order of 10¿6cm thick, on a mica strip 0.3¿0.4 wide, located symmetrically in the transverse plane. The change in resistance or rise in temperature can be used as a measure of input power, which is determined by a d.c. calibration. The operating bandwidth, for a given waveguide, is greater than that normally available with thermistors and bolometers, and the techniques described seem especially convenient for the calibration of these instruments. Good agreement has been obtained in a comparison with calorimeters and a force-operated wattmeter, and the results indicate that an error limit of not more than ±3% can be achieved at a frequency of 10 Gc/s.
