Power and temperature dependence of passive intermodulation distortion

Passive intermodulation (PIM) distortion occurs when a supposedly passive microwave structure spreads the spectrum of an applied radio frequency signal. A two-tone test is used to explore the temperature and power dependence of upper and lower PIM resulting from an SMA termination with an applied 900 MHz signal. PIM is shown to have the classic inverse frequency dependence on the frequency separation of the tones. The power dependence has the classic three-to-one slope of a third-order polynomial nonlinearity although the generating mechanism is quite different and results from resistance variation due to heating by the varying envelope of the two-tone beat signal. Temperature is seen to affect the upper and lower sideband PIM differently and both are correlated to the variation of the termination's resistance with respect to temperature.