The Distributed Antenna System (DAS) has, in the last few years, begun to prove all of the claims made for it, like ubiquitous coverage in huge stadiums and multi-stadium events and delivering wireless capacity where it could never be achieved before. These installations are truly incredible feats of engineering, planning, and installation, and they all have one thing in common: the need to maintain low levels of Passive Intermodulation Distortion (PIM).
At events like the World Cup and the Olympic Games there are thousands of places where PIM can be encountered, and because today's higher-order digital modulation schemes simply will not tolerate this insidious invader, it must be resoundingly dealt with everywhere it could potentially appear. If this is not considered a primary objective, even if a system demonstrates excellent PIM rejection when deployed, it can fail after year in service. PIM can be present at any of the thousands of places in a large DAS system that transmit or receive LTE (and soon LTE-Advanced) signals, so low-PIM connectors must be used in each one, and measurements must be made to ensure no errant signals are present.
Many of you may have noticed that PIM requirements have become more stringent than anyone would have guessed even 5 years ago, and keeping it in check requires passive components specifically designed to achieve levels of -150 dBc or better. It is a major challenge for manufacturers as it presses the envelope, so to speak, of what can realistically be achieved. However, San-tron has proven that it can be done.
The next challenge for DAS systems is what occurs after the system has been in place for a long time; during which rust, corrosion, and component wear can turn what, upon deployment, was a pristine system into a generator of signals that degrade receiver sensitivity and if strong enough can render some portions of the allocated spectrum unusable.
The answer is to use cables, connectors, and cable assemblies built to deliver excellent PIM performance for many years thanks to their design and the materials from which they are constructed. Materials must be carefully chosen to reduce or eliminate the possibility of degradation over time even when deployed in corrosive or otherwise hostile environments. Cable assemblies designed specifically for the conditions encountered by DAS systems are essential.