Why does Passive Intermodulation (PIM) matter to Weibonuo as Antenna Manufacturer?
Introduction of PIM
PIM is a growing issue for cellular network operators. PIM issues may occur as existing equipment ages, when co-locating new carriers, or when installing new equipment. PIM is a particular issue when overlaying (diplexing) new carriers into old antenna runs. PIM can create interference that will reduce a cell’s receive sensitivity or even block calls. This interference can affect both the cell that creates it, as well as other nearby receivers. PIM is created by high transmitter power so on-site PIM testing needs to be done at or above the original transmitter power levels to make sure that the test reveals any PIM issues. PIM is a serious issue for cellular operators wanting to maximize their network’s reliability, data rate, capacity, and return on investment. It is worth noting that PIM testing does not replace impedance-based line sweeps, rather, it complements line sweeping, which is now more important than ever. High-speed digital data communications make PIM testing critical. As cell usage and throughput grows, the peak power produced by the new digital modulations increases dramatically, contributing heavily to PIM problems. On-site experiments have shown significant decreases in download speeds linked to slight increases in PIM.
The Importance of Low PIM Antenna
Antennas are a critical part of any transmission system. They take the full power of the signal, or signals, and if they create any PIM, it will be broadcast along with the rest of the signal. If also used for reception, the PIM is already in the conductor, with no transmission loss, ready to cause harm to reception.Antennas are subject to fatigue breaks, cold solder joints and corrosion. Because of the mechanical nature of PIM generation, standards bodies recommend tapping the antenna lightly during PIM testing to see if that creates PIM spikes. It is also possible to test the antennas on the ground prior to installation, something that is highly recommended. Care must be exercised as the antenna will be radiating high RF levels and are particularly susceptible to external near field interference that can result in a false failure. This can be a very difficult test to do in the field and it is therefore a good idea to put the first good antenna aside and retest it periodically to ensure your environment or test setup has not changed. Any device that tests well can have a failure confirmed by pointing the antenna at a fence, dumpster or any other sizable metallic structure as this always creates an external PIM source. This result can then be measured on a test set to confirm that a faulty condition would be seen. Weibonuo Antenna achieve -150dBc for base station antenna and -155dBc for in-building antenna portfolios.