Conductivity Measurements at Microwave Frequencies

Because of the skin effect, the surface condition of conductors becomes very important in determining attenuation at microwave frequencies. This has been investigated by measuring small wire samples at a frequency of about 9,000 megacycles. A sample of the wire to be measured is inserted in a metal tube to form the center conductor of an open-ended coaxial line. The ratio of the peak frequency to the half-power bandwidth of this coaxial-line resonator, measured with the aid of an oscillographic display of its amplitude-versus-frequency characteristic, gives its loaded Q. The amplitude characteristic of the frequency-modulated signal generator, on which a wavemeter marker appears, is viewed simultaneously and used as a reference. By correcting the result to obtain the unloaded Q of the center conductor alone, the effective conductivity of the sample is obtained. Results of measurements on a number of samples of different conductors having various surface conditions, treatments, and platings are given. These results are of value in the design of microwave components of all types where loss is a factor of importance.