Measurement and Mitigation of Passive Intermodulation Distortion

Passive intermodulation (PIM) causes unwanted distortion signals in high power radio systems such as satellite links, wireless base stations, and harmonic radars. In general passive wireless components such as cables, connectors, filters, and antennas are linear and thus do not create intermodulation. However, under high powers this is sometimes not the case and PIM is generated. The physical mechanisms causing PIM are not well understood, partially because they are difficult to measure. Furthermore strategies to reduce PIM in system design are sparse. In this thesis PIM measurement techniques are developed and demonstrated which enable differentiation and physical understanding of PIM leading to reduction of PIM in future high power systems. First, measuring higher order intermodulation products is shown to reveal significant information about the PIM source. For example, this information allows the differentiation of two types of coaxial connectors which would appear identical using standard PIM measurement techniques. Second, the standing wave of voltage and current inside a resonator is used to increase the voltage and current selectively at the PIM source. This method extends the measurement sensitivity of any system, and also allows differentiation between voltage and current induced PIM sources. Finally, two mitigation techniques are presented which leverage measurement capabilities developed in this thesis to give low PIM design techniques for systems. The first is a method for designing matching networks to reduce the effect of PIM generating components, and the second uses a magnetically tunable network to cancel PIM sources