PIM Shield® Paint & PIM Seal™ Caulk
It has taken more than 3 years to develop, but it’s finally here! PIM Shield® Paint & PIM Seal™ Caulk are new liquid RF barrier products from ConcealFab designed specifically for reducing external PIM at cell sites. These new materials create effective and reliable RF shields able to reduce energy arriving at covered PIM sources. Lab tests have demonstrated >30dB IM3 reduction on PIM sources covered with a single bead of PIM Seal™ Caulk or with two coats of PIM Shield® Paint.
The challenge with this product was not finding a conductive paint. EMI shielding paints are readily available that are designed to be painted on interior walls to provide shielding from cell phone towers, radio broadcasting antennas, etc. The challenge was finding a conductive paint that was also “stretchy” enough to not crack when used in outdoor environments. The existing paints that ConcealFab tested were relatively brittle and cracked easily when deployed in thick sections or when exposed to thermal cycling.
Small cracks may not be a problem when you are creating an EMI shield to block weak signals far away from a radio transmitter. Cracks are a problem, however, when trying to mitigate PIM near high power base station antennas. Cracks in conductive coatings create lightly touching metal-to-metal surfaces that can become PIM sources. ConcealFab has seen cases where cracks in a conductive coating created worse PIM than the original PIM source we were trying to mitigate!
ConcealFab worked with industry experts to tackle the cracking problem and after years of co-development is now able to offer highly elastic conductive coatings able to withstand harsh outdoor environments. An Application Note is available from ConcealFab that describes the extensive testing done to validate the RF as well as mechanical performance of these new materials.
PIM Shield® Paint can be applied by brush or roller to a wide variety of surfaces near base station antennas. PIM Seal™ Caulk is a thickened version of PIM Paint designed for filling small gaps and for direct application to metal interfaces on the antenna mounting frame. PIM Seal™ Caulk comes in 10.5 oz tubes and can be applied using a standard caulk gun. Surface preparation requirements as well as application information are provided on the product labels as wall as in the technical datasheets.
While slathering everything on the antenna mounting frame with paint to eliminate PIM sounds tempting, operators should continue to replace “PIM Prone” cable support hardware with proven low PIM alternatives. ConcealFab’s new liquid solutions should only be applied at locations that are difficult or expensive to mitigate using other methods. PIM Seal™ Caulk and PIM Shield® Paint are not magic solutions for solving all external PIM problems at cell sites. They are, however, important “tools in the tool bag” in the ongoing battle to cost effectively eliminate PIM interference and improve network performance.