Broad-Band Power-Measuring Methods at Microwave Frequencies

Two broad-band methods of measuring power at microwave frequencies have been investigated. In both methods, the normal load termination may remain connected to the microwave generator while the power is being measured. The first method makes use of the forces due to the electromagnetic fields in a transmission system to cause displacements of a diaphragm or membrane. This displacement is proportional to the square of the actuating fields and is made to operate an indicating system which gives output proportional to the microwave power. In the second method, thin films on a skin-depth scale are inserted in a microwave transmission system so as to cause only small discontinuities. A small fraction of the total power, usually 1/1800 to 1/200, is dissipated in the film. The indicator system measures the temperature rise of the film, ordinarily as a function of its resistance change, and output is again proportional to the microwave power. Continuous characteristics have been measured from 1,000 to 10,000 Mc, with additional isolated data at about 300 kc, 5 Mc, and 300 Mc. Both methods give a calibration flat to better than ±1 db between 1,000 and 10,000 Mc with gradually reduced sensitivity at lower frequencies for the tellurium-zinc unit