Non-Linearities of Flange Connections in Transmission Lines Carrying High RF Power

Because of the non-linear characteristics of current-carrying contact areas in waveguides and coaxial connectors, combination frequencies with very small amplitudes are generated, when these components are to carry two or more frequencies. Inmicrowave systems these mixing products of odd orders cause interfering intermodulation noise. The amplitudes of the non-linear distortions are primarily determined by the magnitude of the contact pressure and by the amplitude of the current flowing through the contact. A test set-up for determining the level of intermodulation noise is described and test results are shown, which have been gained at RF powers of up to 1000 Watts in the 2 GHz band. They indicate that the interfering power of the combination frequency of the third order is up to 500 Watts in good agreement with the theory, being proportional to the third power of the applied signal power. Measurements on flange connections contaminated with salts of metals indicate similar characteristics.