Passive intermodulation (PIM) effects are caused by non-linearities in passive products such as connectors. When two (or more) signals are present the PIM products from a non-linearity are just like those from a mixer i.e. the sum and difference products of the two frequencies. This unwanted frequency generation can be tolerated in some systems as the PIM signal levels are low, often 100dB or so down on the main signal levels.

A designer of a prototype radio for a defence electronic warfare (EW) project needed to find a surface mount switch with high power handling capability and very low insertion loss over a very wide frequency range. Looking at conventional MMIC solutions he was having to make some unwanted compromises.