Passive intermodulation and its effect on space programs

Intermodulation products are generated when multiple frequency signals are applied to a circuit element having a non-linear input/output characteristic. The space community first became aware of passive intermodulation (PIM) problems due to the difficulties encountered by the Fleetsatcom program. The concern with PIM remains today. Following a discussion of how past and present space programs concerned with PIM resolved the difficulties this paper provides a guide for selection of materials, typical PIM test set and facility designs including the design of a thermal enclosure to perform PIM test at temperature extremes. The paper concludes with a description of some facilities capable of performing PIM measurements on large reflector assemblies and complete satellites