Analysis of Passive Intermodulation in a Junction: Physical Simulation Models for Non-Linear Electrical Contacts

Passive intermodulation (PIM) is a growing issue in several communication systems, like cellular networks, shipboard systems and satellite communication systems. These intermodulation products are due to the non linear behaviour of passive components in which the signals travel. But, unlike the more known distortions due to active devices, they are more complicated to remove and can lead to problems during the communication. Indeed, these unwanted frequencies can fall within the receiver band, leading to interference problems and reducing the performance of the whole system. Specifi cally, the arise of PIM is related to the non ideal metal-metal (MM) contacts in the system. The goal of this thesis is to develop an equivalent circuit model able to describe the behaviour of a MM joint. In order to do this, two different approaches have been considered: a physical-based model and a behavioural-based one. A physical-based approach allows to develop a general model for the contact based on mathematical equations. But, such a model is difficult to develop due to the different microscopic effects which influence such a junction and the several parameters that should be accurately estimated. On the other hand, the behavioural-based approach allows to overcome the above issues, thus providing a reliable modeling scheme. Several experimental setups and measurement confi gurations have been considered. Among them, the setup based on a steel-copper contact provides the most stable confi guration. Thanks to a spectrum analyzer, we were able to observe PIM and, analyzing the chosen setup, it was possible to develop a model able to fully characterize the behaviour of the above contact. Furthermore, the model was validated by comparing the experimental results with the ones predicted by the proposed behavioural-based model via simulations through a full-wave solver (e.g. CST Microwave Studio).