With the consistent demand for wireless connectivity, organizations and IT managers must take a closer look at how this technology affects their current infrastructure. One element garnering much attention is intermodulation.
According to a recent HUBER+SUHNER white paper, when intermodulation occurs in a system, new frequencies are being created. Diodes (News
- Alert), which are non-linear components, are frequently used in intermodulation for wireless connectivity.
Intermodulation is not used in all applications. In communication systems, when reception paths and transmission paths are combined, intermodulation does not occur. At some points in wireless connectivity technology, there comes a time for passive intermodulation.
Non-linear systems, which put out a much different output signal shape, use passive intermodulation. Passive intermodulation poses a problem when low power and high power signals are sent out at the same time, but at different frequencies.
Problems for the operators, including those involved in wireless connectivity, occur when distortion is created by a received signal and an intermodulation signal that fall into the same frequency band. The distortion renders a band unusable, which affects the capacity of the communication site.
So what is causing passive intermodulation (PIM)? One place to look is at the physical components such as the metallic and dielectric materials. Generally, it’s the exotic metals in dielectrics that cause trouble. Nickel, because of its non-linear magnetic flux density, often causes PIM.
And while it would seem an easy problem to avoid – simply don’t use any metals that could create the non-linear issues – even the slightest ferromagnetic contamination creates distortion and PIM. Wireless connectivity companies have found some success, however, using silver. Dielectrics that are plastic-based don’t create these problems.When considering galvanic contacts, PIM is a frequent issue because the contacts are susceptible to PIM. Dielectric coatings in these contacts are typically very thin and electron tunneling can occur, which creates a non-linear atmosphere.
Another problem spot in these contact areas has to do with heating. The spot has a high current density where joule heating occurs, which creates a non-linear situation. But PIM issues are also hinging on contact force. Transient distortion arises when the small contact areas experience high current densities, causing contact points to move.
Simply knowing the source of PIM doesn’t make it go away. Proper design is the key to prevention. If problems occur and the high-quality source plating has been used as a base material, all that needs to be done is a check on contamination and magnetism and the source of the problem is found. Low PIM products are clean – any sign of dirt will block a path and create non-linearity.
When it comes to intermodulation, not all applications are created equal for the wireless connectivity environment. Some are more sensitive to intermodulation than others. A way around the issue is through careful engineering and design, which is offered by HUBER+SUHNER.
Edited by Jamie Epstein