What does low PIM really mean?
By
Amphenol RF
Figure 1: Low PIM Connector (Source: Amphenol)
Low PIM is the buzzword of the week in wireless
infrastructure as the industry decides on the new “standard” RF connector. PIM stands for Passive Intermodulation
(which is similar but not the same as IMD – that is for active components) and is measured in dB’s. PIM is defined
as the unwanted signal or signals generated by the non-linear mixing of 2 or more frequencies, but what does it
really mean to the consumer? High PIM means poor cellular reception and limited bandwidth to the end user, which in
turn means lost customers to the carrier. Low PIM means strong signals with more bandwidth for more users, which
means happy customers and higher revenues for the carrier. From a hardware perspective, it means that each and every
connection must be designed to minimize PIM and tested to ensure it is installed properly. That is where Amphenol is the expert.
"Amphenol has been testing and optimizing PIM in our connectors for almost two decades."
Current Hardware
The current standard wireless RF connector – 7/16
connectors – are large and heavy. They have been in the field for years, are proven to be reliable, and have
good PIM performance. However, in the age of smartphones, increased data usage equates to increased RF connector
density, and the 2”x 2” flange required to mount a 7/16 is too large.
Figure 2: 7/16 Connector (Source: Amphenol)
The current alternative – N type connectors – are smaller and fit on a 1”x 1” flange, but cannot match the torque
spec or PIM performance of the 7/16 connector.
Figure 3: N-Type Connector (Source: Amphenol)
Connection Evolution
The front runners for the crown are the 4.1/9.5 and
the 4.3/10 connector. The 4.1/9.5 connector is an old interface and is
commercially available, but has not achieved widespread adoption. The 4.3/10 is a new interface based on a new
specification, with nearly no time in the field. Let’s compare the two technically first, then understand the
industry forces acting on the choice of next gen connectors:
- Both meet or exceed the performance of the 7/16, but fit on a 1” flange
- Both can handle higher torque loads than N type, reducing install failures
- 4.1/9.5 PIM performance varies when loose or under strain (similar to 7/16)
- 4.3/10 has the unique ability to have stable PIM while connector is loose or under strain – this increases
reliability and allows it to be hand tightened
- 4.3/10 has separate mechanical and electrical planes for optimized PIM
Figure 4: 4.1/9.5 Bulkhead Flange Adapter (Source: Amphenol)
Industry forces:
- A major US carrier is pushing all large RF interfaces to 4.1/9.5
- European standard is likely to be 4.3/10
- Many carriers have not adopted 4.1/9.5, seemingly waiting for the 4.3/10
While Verizon is supporting 4.1/9.5 at the moment, the industry at large seems to be holding off as the 4.3/10 is a
strong contender for the crown of “Standard Low PIM” connector. Very likely both standards will exist and create
their own niche, as is seen with the current gen products. Amphenol continues to broaden its industry leading
product portfolio, offering the 4.1/9.5 in multiple configurations, and developing the 4.3/10 product line.
Figure 5: 4.1/9.5 Adapter (Source: Amphenol)
