Passive intermodulation distortion (PIM) has always been a thorn in the side of communications and other systems relying on the electromagnetic spectrum. However, the higher-order digital modulation techniques and high data rates employed in today's wireless systems-- as well as extremely dense channel spacing-- have made it a greater issue than ever.

Passive intermodulation is the spurious generation of nonlinearities when two or more signals are present in a passive, non-linear component that causes a mixing action that results in new signals related to the originals. If the extraneous signals appear in the receive bandwidth of a communications system, the system noise floor is increased, which reduces receiver sensitivity and increases bit-error rate, and overall degradation of system performance. In the past it was possible to avoid these interfering signals by moving to a different channel, but the densely-packed spectral environment today makes this impossible. If the interfering signals are strong enough they can actually block a receiver and shut down a sector of a macro cell.

PIM most frequently occurs in connectors, switches, isolators, couplers, cables and other common transmission line components. As PIM can arise in an almost unlimited number of sources it is one of the most difficult problems to solve. Typical examples include rusted or corroded contacts, surfaces contaminated by dirt, dust, or moisture, loose or misaligned connectors or other junction points, tiny pieces of metal inside connectors, and the aging of components and systems that have been in service for many years. The problem is compounded by the fact that signals created by PIM can be strong enough to affect systems far from the one they are degrading.

The sensitivity of wireless systems to such degradation has increased requirements for PIM reduction to extremely low levels, first about -150 dBc now as high as -165 dBc. This is an extremely low level and until relatively recently there were few instruments capable of measuring such levels.

San-tron has developed cable assemblies, adapters, and other transmission line components that reduce PIM to levels of -168 dBc, and efforts are underway to reduce this even further with advances from the materials level through design and fabrication. It's a continuous challenge and one that is unlikely to retreat.

For more information about San-tron's low-PIM products, visit: